CHEM 1152L Lab Manual 2023
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School
University of North Georgia, Gainesville *
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Course
1152
Subject
Chemistry
Date
Feb 20, 2024
Type
docx
Pages
80
Uploaded by LieutenantOyster1881
CHEM 1152L Lab Manual – Page 1
Name: ______________
Partner’s name:
______________
Lab Time:
______________
Lecture Time:
______________
Experiments
for
Chemistry 1152L
CHEM 1152L Lab Manual – Page 2
Table of Contents
Table of Contents
Chemistry Laboratory Safety Agreement
Logger Pro Directions
Graphing Instructions
Presenting and Analyzing Data in Science
How to use Chemistry Lab Equipment
………………………………………………...…10
Organic Modeling Part 1
Organic Modeling Part 2
Paper Chromatography
Why is the Cat Sick?
Preparation of Acetyl Salicylic acid (Aspirin)
Characterization and determination of purity of Aspirin
Preparation of Soap
Oxidation Lab
51
Polymers
………
.…….………………………………………………………………………
....
55
Household Chemicals Assignment ……
………………………………………………
....
60
Lipids Lab …
…
.…….………………………………………………………………………
....
63
Protein Lab...
…
.…….………………………………………………………………………
....
70
Working with Enzymes-Lactase
76
CHEM 1152L Lab Manual – Page 3
Chemistry Laboratory Safety Agreement
When I am in the laboratory, I will:
1. wear approved eye protection at all times;
2. wear sensible clothing and tie back long hair;
3. Avoid absorbing chemicals into my body by
-
using great care in detecting odors,
-
never putting anything in my mouth,
-
washing skin and clothing that contact chemicals;
4. not attempt any unauthorized experiments;
5. know where safety equipment is and how to use it;
6. never work alone;
7. use the fume hood when necessary or so directed;
8. dispose of waste and excess materials according to instructions;
9. use only equipment that is in good condition;
10. assemble apparatus carefully;
11. avoid touching hot objects;
12. use extreme caution when inserting glass tubing into stoppers;
13. keep the laboratory clean;
14. handle chemicals with caution by
-
reading labels carefully,
-
using only the amount required,
-
leaving chemicals in their proper places,
-
leaning up all spills immediately with supervision,
-
labeling all containers to identify their
-
contents;
15. thoroughly wash my hands and face at the end of each laboratory period;
16. take immediate action as needed in response to burns, splattered chemicals,
fire, or injuries;
17. report all accidents and injuries, no matter how minor, to my laboratory instructor.
I have carefully read and fully understand all the safety precautions summarized above. I recognize that it is my responsibility to observe the precautions throughout my chemistry course.
_____________________________________________ ____________
Signature
Date
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CHEM 1152L Lab Manual – Page 4
Logger Pro Directions
1.
Plug the appropriate sensor into CH1 of the LabPro computer interface.
2.
Connect the LabPro computer interface to the computer using the USB cable. The LabPro computer connection is located on the right side of the interface.
3.
Provide power to the LabPro interface by plugging the AC power supply to an electrical outlet.
4.
Once logged in to the network, start the logger pro software (it can be found following the path: Start
UNG Menu
Science
Logger Pro. A window may
open that reads “Set up Interface”. If this happens, select from the drop down menu the port that reads “Lab Pro – USB” and click OK. If you are not allowed to select this option, close out of the program and check all connections to the LabPro and ensure that they are plugged in correctly.
5.
After the computer has recognized the Lab Pro, click on “File” and then “Open…”
Click on the “Chemistry with Vernier” folder and select the appropriate file for the experiment.
6.
Modify the experiment set up values, if needed, to suit the needs of the particular
experiment. If you need to change the vertical or horizontal scales, do it by clicking the mouse on the uppermost or lowermost scale numbers and typing the new values.
7.
The specific way of collecting data will depend on the experiment being performed.
8.
Save your data to your home folder BEFORE printing.
9.
Disassemble the set up, clean the sensor and return all parts to their original location.
CHEM 1152L Lab Manual – Page 5
Graphing Instructions
Making a Graph in the latest version of Excel
1. Open Microsoft Excel. Type the x-values into the “A” column and the y-values into the
“B” column. Do not include units with the numbers (this only confuses Excel). We indicate the units being used with axis labels.
2. Highlight all numerical values you wish to graph. Click “Insert” at the top of the page and choose ”Scatter.” Do Not connect the dots with a line, just plot the raw points.
3. Now Click “Design” at the top of the screen and look for the section labeled “Chart Layout”. Click the mini chart that looks like it has a label on the axes and a place for a title. Label the axes with a description and a unit, and include a creative title.
4. Right Click on one of your data points. Choose “Add Trend Line” and check the box for “Linear” and then to “Display Equation on Chart.” Recall the equation for the line y = mx + b and that slope is rise over run. The slope of a line from experimental data often yields valuable information.
Making a Graph in Logger Pro
1. Open Logger Pro. It can be found on any computer on campus by going to the Start Menu, click on UNG Menu, and then on Science.
2. Enter your data into the columns labeled X and Y
, but do not include units with the numbers (this only confuses Logger Pro). We indicate the units being used when we label the axis.
3. Double click on the X at the top of the data column. Type in the axis name and indicate the appropriate units. Repeat this for the Y column. Labeling these columns should automatically update the graph also.
4. On the graph itself, double click in the open space and add a title for your graph.
5. Click on the tab at the top “Analyze” and choose linear fit.
CHEM 1152L Lab Manual – Page 6
Presenting and Analyzing Data in Science
PRESENTING DATA
Well–constructed data tables and graphs are loaded with information. The reader should be able to determine what the lab is about and the major results by looking only at the data section of a report. An independent variable is the factor that is controlled or manipulated by the experimenter. An easy way to identify the independent variable is that it is decided or known before the experiment begins. The dependent variable will depend upon the independent variable. In other words, the dependent variable would be the results of the experiment. TABLES:
4 Key Points
TITLE:
There does not exist one set way to title a table; however, it should describe the data that it contains. To help you get started two common styles are described below. One way takes the general format, “The [effect(s)/dependence]
of [independent variable] on the [dependent variable] (See example 1). Another choice follows the format, “[Description of dependent variable] for different [independent variables] (See example 2). STRUCTURE:
Make vertical columns in the following order: the independent variable, the dependent variable, the calculated results (if needed), and comments (if needed). Multiple trials should be subdivided into columns instead of creating more tables. The data for the independent variable should be listed in order, usually from smallest to largest. Refer to examples 1 & 2 for clarification. LABELS:
Each vertical column should be labelled to describe the variable that is listed beneath it. Try to be somewhat detailed. For instance, it would be much better to put “Average time needed to melt ice” rather than just “Time”. UNITS:
The units generally appear with the labels for each column. Comparisons between data will be easier if you do not mix units (i.e. cm with m). Example 1. The effects of Miracle-Gro concentration on growth of radish plants.
Fertilizer concentration
(grams per 100 mL H
2
O)
Plant height after 6 weeks
(centimeters)
0.5
2.8
1.0
3.4
1.5
3.7
2.0
4.2
2.5
3.9
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CHEM 1152L Lab Manual – Page 7
Example 2. Reaction times for the iodine clock reaction for different concentrations of
KIO
3
. Molarity of KIO
3
Reaction Time (s)
Trial 1
Trial 2
Trial 3
Average
0.10
49
47
50
48.7
0.20
25
26
25
25.3
0.30
15
15
17
15.7
0.40
12
11
14
12.3
0.50
10
10
9
9.7
GRAPHS:
Overview:
There are two main types of graphs that are most frequently used—line graphs and bar graphs (also called histograms). Line graphs should be used when the areas between data points have meaning. For instance, if you measured the length of your hair once a week for 12 weeks then a line graph would show the expected values for every point between your actual data points. Bar graphs should be used when the intervals between data points have no meaning. As an example, suppose you measured the top speed of different animals. A line graph of this
data might infer that there exists an infinite number of animals in between cats and dogs. Line Graphs:
6 Key Points
Title:
Follow the guidelines given for writing a title for a table. Structure:
The Y–axis (vertical) is used for the dependent variable and the X–axis is used for the independent variable. X and Y values should increase uniformly as you move to the right and upward, respectively. Scaling:
Graphs should take up from one third to a full sheet of paper. The contents of the graph should fill most of space outlined by the axes. In order to do this it is important to note that the numbering of the graph does not have to start at 0. Start numbering at a point that is slightly lower than the lowest data value and stop numbering slightly higher than the highest data value. The range of values for each axis should be subdivided using tick marks. Use as many tick marks as can be conveniently labeled. Labels:
Each axis should have a detailed label to describe the appropriate variable. Units:
Indicate the proper units in parentheses next to each axis label. Paper:
All graphs should be done using graph paper unless created via computer. Bar Graphs:
6 Key Points
CHEM 1152L Lab Manual – Page 8
Title:
Follow the guidelines given for writing a title for a table. Structure:
The Y–axis (vertical) is used for the dependent variable and the X–axis is used for the independent variable. Y values should increase uniformly as you move upward. The variables on the X–axis are often grouped to make trends (or
lack of trends) easier to identify. Scaling:
The numbering of the Y–axis should start at a point that is slightly lower than the lowest data value and stop numbering slightly higher than the highest data value. The X–axis should have equal subdivisions Labels:
Each axis should have a detailed label. Note: The X–axis (independent variable) will have labels for each bar and an overall label. Units:
Indicate the proper units in parentheses next to each axis label. Paper:
All graphs should be done using graph paper unless created via computer. Example 3. A proper line graph
Example 4. A proper bar graph
ANALYZING DATA
During some of the labs you will be asked to determine either the percent difference
CHEM 1152L Lab Manual – Page 9
between two data points or the percent error of a data point. Use the following equations to calculate these numbers.
% difference = |(
data point 1
)
- (
data point 2
)|
average of data points
x 100%
% error = |
theoretical value - experimental value
|
theoretical value
x 100%
PROBLEMS
Create a table and a graph for each set of data described below. 1. A student tests the amount of caffeine found in 12 ounce portions of some popular soft drinks. He finds that Coca–Cola contains 45 mg, Mountain Dew contains 54 mg, Dr. Pepper contains 41 mg, Pepsi contains 36 mg, and Jolt contains 71 mg. 2. A class of students tries to find the density of mercury by measuring the mass of mercury samples that have different volumes. Group 1 measured the mass of 20.00 mL of Hg to be 271.90 g; Group 2 measured 30.00 mL of Hg to be 407.94 g; Group 3 measured 26.00 mL of Hg to be 353.44 g; Group 4 measured 28.00 mL of Hg to be 380.61 g; Group 5 measured 24.00 mL of Hg to be 326.25 g; and
Group 6 measured the mass of 22.00 mL of Hg to be 299.08 g. The density is the slope of the graph for this data. Look up the density of mercury calculate the percent error. 3.
A chemist measures the volume of a gas at various pressures. The volumes she
measured are in parenthesis next to each pressure that was tested — 1.00 atm (4.02 mL), 1.30 atm (3.10 mL), 1.60 atm (2.51 mL), 1.90 atm (2.11 mL), and 2.20
atm (1.84 mL). Include 1/P in your table and graph 1/P versus volume.
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CHEM 1152L Lab Manual – Page 10
How to Use Chemistry Laboratory Equipment
Top loading balance
Buret
Pipette with bulb
Balances
:
1.
Do Not
zero out (tare)
the balance
or use a weigh boat
unless you are instructed to do so by your lab instructor.
2.
The accepted practice is to Weigh by Difference: (this means you will record 3 masses)
(a)
Record the mass of the empty container
(b)
Record the mass of the container plus the substance being weighed
(c)
Subtract to find the mass of the substance, alone.
(d)
Use the same balance for both measurements.
3.
Always record every digit from the digital readout of the balance.
This means all masses should be recorded to the 3 decimal places.
4.
Do not add chemicals to a container while it is on the balance.
5.
If you spill on the balance or around the balance, clean it up immediately. Chemicals left on the balance will corrode and damage it. Brushes are provided and can be used to sweep the solid into a paper towel or weigh boat before being thrown in the trash or appropriate waste container.
CHEM 1152L Lab Manual – Page 11
Pipettes
:
1.
Do Not
use a pipette with a 10 marked at the bottom.
2.
Rinse the pipette
prior to measuring and transferring the desired amount of liquid/solution:
Rinse first with distilled water several times from a squirt bottle
Secondly, rinse 2-3 times with the solution/liquid to be measured. To do this, draw the solution into the pipette past the volume you wish to measure. Then allow the liquid to drain out into the sink or appropriate waste container. 3.
To fill the pipette
:
(a)
Place the pipette into the solution/liquid with the tip resting on the bottom of the container.
(b)
Squeeze the air out of the pipette bulb and set it on top of the pipette.
(c)
Slowly release the bulb and allow the solution to be drawn into the pipette.
(d)
Fill the pipette past where you want to measure.
(e)
Remove the bulb and quickly replace it with your finger tip or thumb.
(f)
Pull the pipette completely out of the liquid and slowly allow the solution to drain down to the mark appropriate for the volume you wish to measure.
You will have better control if you do not remove your finger entirely and the (g)
If you let too much drain out, simply place your finger back on the top of the pipette and repeat steps (b) – (f). There is no need to let all of the solution drain out before attempting
to fill it to the correct volume again.
(h)
Measure at the bottom of the meniscus. The bottom of the dip should rest on the appropriate mark on the pipette. (see Diagram A) (i)
With the correct amount of liquid in the pipette and your fingertip or thumb securely on the top of the pipette, pick up the pipette and move it above (or into) the container where the solution is needed.
(j)
Remove your finger/thumb and allow the solution to drain out entirely into the desired container
IF, and only IF,
your pipette is marked “blow out
”, then take the pipette bulb and blow out the last few drops of solution remaining at the tip of the pipette into the beaker/flask where
you have transferred the solution.
4.
Do not
draw liquid into the pipette bulb or remove the pipette from solution with the bulb still attached. (This is Bad, Bad, Bad technique
, makes a mess and deteriorates the bulb! It also angers the instructor and will result in a loss of points
)
5.
There is no need to jam the bulb onto the pipette. Placing it on top of the pipette is all that is required to make a proper seal. 6.
Rinse the pipette thoroughly with distilled water once you are done using it. 7.
The pipette can consistently deliver volumes with uncertainty in the hundredths place. Thus, all volumes from a pipette should be recorded to 2 decimal places
. For example: 5.00 mL
CHEM 1152L Lab Manual – Page 12
Burets
:
1.
Pour out the contents of the buret
into the sink. If the buret was stored properly, it is only distilled water.
2.
It is useful to have a waste beaker handy while working with a buret.
3.
Rinse the buret thoroughly with distilled water, making sure to allow some water to drain through the tip as well.
4.
Rinse the buret 2-3 times with the solution you are going to fill it with. Pour 5-10 mL of solution into the buret with the stopcock closed. Invert the buret to allow the solution to run out the top of the buret while
slowly turning it in your fingers to rinse the entire barrel of the buret. Additionally, drain some of the solution through the tip of the buret.
Make sure the rinsing solution is emptied into an appropriate waste container, or sink. 5.
You are now ready to fill the buret. Make sure the stopcock is closed (see Diagram B) and there is a waste
beaker under the buret. Using a funnel, pour the desired solution into the buret until it is near the top. Do not overfill the buret
. Remove the funnel.
6.
Check for air bubbles in both the tip of the buret and the barrel of the buret.
To remove air bubbles from the tip, quickly turn the stopcock a half turn and allow a small amount of solution to drain out into a waste beaker. Repeat a if necessary.
To remove air bubbles from the barrel, tap lightly on the side of the buret.
7.
If the liquid level is above the 0 mark, you will need to drain some of it into a waste container until the liquid level is on the scale.
You do not need to make sure that the buret is filled exactly to the 0 mark.
Doing so is generally a waste of time and chemicals. 8.
You are now ready to dispense liquid/solution from the buret. Before you do so, you need to first make an initial reading of the volume on the buret.
Place the container you wish to collect the liquid in under the buret. To avoid significant splashing, make sure the tip of the buret is below the lip of the beaker or flask. 9.
Dispensing liquid from the buret is simply a matter of turning the stopcock. Vertical is completely open. Horizontal is completely closed. You can control the rate by adjusting the stopcock somewhere in the middle. (See Diagram B)
10.
Reading the buret:
(a)
Measurements with the buret require 2 readings: an initial and
a final volume. (b)
You may raise or lower the buret to assist you in reading the volume. You may also wish to place your hand or a piece of white paper behind the buret to more clearly see the liquid level in the buert.
(c)
Read at eye level and at the bottom of the meniscus (see Diagram A)
(d)
Always estimate 1 decimal place past the markings. This means all volumes are recorded to 2 decimal places!
If the meniscus is right on a mark, then record the last digit as a zero.
(e)
Do not subtract the number from 50.
Read and record the volume indicated on the buret. You are not measuring how much liquid is in the buret, but how much you are pouring out of it. 11.
Depending on the experiment, you may need to refill the buret before repeating a second trial. However, as long as you are using the same solution you do not need to empty it and re-rinse it before continuing.
12.
When you are done with the buret, drain the remaining contents and rinse thoroughly with distilled
water. Fill the buret with distilled water and return it to its proper storage location.
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CHEM 1152L Lab Manual – Page 13
Organic Modeling
Prelab Exercises
Define these terms:
1.
alkanes
2.
alkenes
3.
alkynes
4.
conformations
5.
structural isomers
6.
stereoisomers
CHEM 1152L Lab Manual – Page 14
Organic Modeling
NAME___________________________
Objective:
This lab will introduce the student to how to draw organic structural formulas, how to systematically name organic molecules, and how to differentiate among the various kinds of isomers. You will need to read the chapters about alkanes and alkenes prior to completing this laboratory.
Part One
I. Drawing Alkanes and Cycloalkanes
Build a model of each molecule given in the table and then, looking at your model, draw the Lewis structure, condensed formula, and bond-line formula for each molecule and give the name for the molecule. Alkanes
Lewis Structure
Condensed
Formula
Bond – Line
Structure
Name
CH
4
N/A
C
3
H
8
C
5
H
12
Alkyl Halides
CH
3
Cl
C
3
H
7
Br
(draw 2
isomers)
CHEM 1152L Lab Manual – Page 15
Structure
Condensed Formula
Bond – Line Structure
Name
C
3
H
6
C
4
H
8
C
5
H
10
C
6
H
12
What is the electron geometry around each carbon in an alkane? _________________
What are the bond angles in alkanes?
_______________
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CHEM 1152L Lab Manual – Page 16
II. Constitutional Isomers
1. Make a model of butane, C
4
H
10
. Change the model so that a different molecule is made by connecting the atoms in a different way. Draw the structures of both isomers using a condensed formula or line structure. Then name them using the IUPAC rules.
____________________________________
_
____________________________________
_
2. Make models of the structural isomers of hexane. Draw their condensed formulas or line structures and name each using the IUPAC rules. ____________________________________
_
____________________________________
_
____________________________________
_
____________________________________
_
____________________________________
_
CHEM 1152L Lab Manual – Page 17
3. Make models of all possible structural isomers of C
3
H
6
BrCl, draw their structural formulas, and name each using the IUPAC rules.
CHEM 1152L Lab Manual – Page 18
Analysis Part Two
I. Alkenes, Cycloalkenes, and Alkynes Build a model of each molecule given in the table and then, looking at your model, draw the structural, condensed and bond-line formula for each molecule and give the name for the molecule. Alkenes
Structure
Condensed
Formula
Bond – Line
Structure
Name
C
2
H
4
C
3
H
6
C
3
H
4
Cycloalkenes
C
4
H
6
C
5
H
8
C
6
H
10
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CHEM 1152L Lab Manual – Page 19
Alkynes
Structure
Condensed
Formula
Bond – Line
Structure
Name
C
2
H
2
C
3
H
4
What is the electron geometry around each carbon with a double bond in an alkene? _________________
What are the bond angles around each carbon with a double bond in alkenes?
________________
What is the electron geometry around each carbon with a triple bond in an alkyne? _________________
What are the bond angles around each carbon with a triple bond in alkynes?
________________
CHEM 1152L Lab Manual – Page 20
II. Geometric/Configurational isomers
1. Make a model of 1,2-dichloroethene. Note that since there is no free rotation about the double bond, you can position the chlorines so that they are on the same side of the
double bond (
cis
configuration) or on opposite sides of the double bond (
trans configuration). Build models of both geometric isomers of 1,2-dichloroethene, draw their structural formulas, and name each.
2.
Build models for geometric isomers of the following compounds, if they exist:
2,3-dichloro-2-butene
2-butene
1-butene
CHEM 1152L Lab Manual – Page 21
III. Aromatic Compounds
1.
Make a model of benzene. Draw the structural, condensed, and bond-line formula. What are the bond angles of the carbons in benzene?
2. Build models for structural isomers of the following aromatic compounds: Draw the structural formulas and name each.
a) dimethylbenzene
b) trimethylbenzene
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CHEM 1152L Lab Manual – Page 22
NAME_________________________ POST-LAB QUESTIONS
1. Fill in the following chart:
ALKANES
ALKENES
ALKYNES
Cycloalkanes
characteristic
bond type
(single, double, …)
bond angles
present
geometry about
bond
saturated or
unsaturated?
General formula
2. Tell if the following are identical, constitutional isomers, geometric isomers, or none of these. Name each compound.
________________________________________
________________________________________
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CHEM 1152L Lab Manual – Page 23
_________________________________
_________________________________
_________________________________
__________________________________
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CHEM 1152L Lab Manual – Page 24
Paper Chromatography
Prelab Exercises
Name: 1.
Define the following terms after reading the lab:
a. stationary phase
b. mobile phase
c. solvent front
d. origin
e. R
f
2.
The following data was collected from a TLC experiment. Calculate the R
f
for each of the dyes.
distance from origin to solvent front
7.5 cm
distance from origin to center of dye A
6.5 cm
distance from origin to center of dye B
2.0 cm
distance from origin to center of dye C
3.8 cm
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CHEM 1152L Lab Manual – Page 25
Paper Chromatography
Objective
After completing this laboratory, the student will be able to separate and identify dyes in a mixture by using paper chromatography.
Introduction
Chromatography is a useful chemical technique that can be used to separate and
identify components of a mixture.
The basic principle of chromatography is the separation of components in a mixture by the repetitive, selective absorption into the stationary phase and extraction into the mobile phase. The stationary phase
is that part of the chromatographic system that does not move. It serves to impede the movement of the solute being analyzed. The mobile phase
is that part of the chromatographic system that moves. It serves to carry the solute being analyzed. In chromatography a solute is first absorbed by a stationary phase to which it is weakly attracted, and then extracted into the mobile phase which is passing through the stationary phase by capillary action. The components of the mixture are separated from each other based on their relative attraction to the stationary phase and their relative solubility in the mobile phase. Solutes which are strongly attracted to the stationary phase will move slower while solutes that are very soluble in the mobile phase will move faster.
. Paper chromatography is useful in identifying the components of a mixture. In paper chromatography, a sheet of absorbent paper is used to provide a stationary phase for an absorbed liquid. the mobile phase (or developing solvent) is a mixture of solvents blended to control the attraction and solubility of the solutes. The choice of developing solvent depends upon the differences in solubilities of the solutes in the solvent. As the chromatogram develops, each component of the solute mixture moves along the stationary phase at a rate of flow that depends on its relative attraction to the stationary phase and its relative solubility in the developing solvent. The pure compound
results into a single spot while mixture can have more than one spots. This rate of flow (R
f
) is measured and calculated to identify the substance or components of mixture. In this experiment the components of the mixture are colored. So, you will be able to use color as an identifier in addition to R
f
. You will obtain an unknown from your instructor that is a mixture of two dyes and spot it along with other known dyes. You will
identify the components of the unknown mixture based on their color and R
f
value.
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CHEM 1152L Lab Manual – Page 26
Procedure
1.
Obtain a 9 x 18 cm sheet of chromatography paper.
2.
Draw an origin line along the long side
1.5 cm from the bottom. 3.
Make 8 evenly spaced spots on the paper starting 2 cm from the edge by putting a small × with a pencil at each spot on the line where a known or unknown sample will be placed. Write a code or identifying number or letter in pencil below each × mark. 4.
Obtain a petri dish bottom. Pour enough 0.1% NaCl to have a 1 cm deep pool of solution in the dish.
5.
Use thin glass capillary tubes to put a very small spot of each sample. Spot the sheet with following dyes in this order from left to right. (Note: If the spot appears faint, allow the solvent dry, then apply a second spot of the same sample on top of the first spot).
a.
FD&C Blue #1
b.
FD&C Blue #2
c.
FD&C Green #3
d.
FD&C Red #3
e.
FD&C Red #40
f.
FD&C Yellow #5
g.
FD&C Yellow #6
h.
an unknown mixture of two of the dyes
6.
After the spots have dried, roll the paper into a cylinder and staple so that the edges are touching but not overlapping
. Place the cylinder in the petri dish. 7.
Allow the solvent to rise up the paper by capillary action until the unknown separates.
8.
Remove the sheet from dish and lay flat on a paper towel to dry.
9.
Make sure you note the relative position of each dye spot on the data sheet after the spots have dried. 10.Calculate R
f
values for the dyes and identify the components in your unknown by comparing the R
f
of known ones.
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CHEM 1152L Lab Manual – Page 27
Data
(Record and label all appropriate data. Attach chromatogram).
Paper Chromatography
Identification of the components in your unknown:
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CHEM 1152L Lab Manual – Page 28
Post-Lab Questions:
1. A Chem1152 lab fellow used an ink pen or a marker pen to write on the chromatography paper? What possibly go wrong here. Provide a simple solution for this
error. 2. What will happen if the sample spots you placed are under the surface level of the solvent?
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CHEM 1152L Lab Manual – Page 29
Why is the Cat Sick?
Objective
The students will use physical properties to identify unknown organic compounds.
Background
Every chemical compound has a unique set of physical properties (density, melting point, boiling point, solubility, polarity, etc). These physical properties are very useful for identification of unknown chemical compounds. This laboratory exercise will focus on the melting point and mobility (distance travelled on TLC plate) of three common over-the-counter (OTC) medicines. Using the data associated with these properties and the medical information related to overdose symptoms, you will be able to conclude Why the Cat is Sick!
Introduction
In an attempt to help his sick kitty, a concerned pet owner administered an over-the-
counter analgesic. Unfortunately, the cat’s condition worsened over the next few days. The owner finally took the cat to a local veterinarian for diagnosis. When questioned, the owner admitted to administering an OTC analgesic but didn’t know the brand or type. The veterinarian suspects the amount of the drug consumed may have caused an
overdose. You and your laboratory partner must analyze the analgesic by the chemical methods outlined to determine what made the cat sick. Note:
No cats were harmed in the writing of this lab.
Meet the Cats
Name:
Pooky
Physical:
female, 4 years old, weighs 8lb. 7oz.
Medical:
All inoculations are up to date, feline leukemia test negative
Symptoms:
When brought to the office, the cat was experiencing convulsions. Prior to
the convulsions she had been vomiting and had lost weight. Lab tests revealed gastric ulceration. Upon opening the bottle, the owner remembered the distinct odor of vinegar.
Name:
Cookie
Physical:
female, 3 years old, weighs 9lb. 5oz.
Medical:
All inoculations are up to date, feline leukemia test negative
Symptoms:
When brought to the office, the cat was lethargic and her lips were blue and swollen. Lab tests revealed liver dysfunction and methemoglobinemia,
with the presence of acetimidoquinone in the blood.
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CHEM 1152L Lab Manual – Page 30
Name:
Jasper
Physical:
male, 1 year old, weighs 7lb. 5oz.
Medical:
All inoculations are up to date, feline leukemia test negative
Symptoms:
When brought to the office, the cat was vomiting. His owner reported that the cat has had diarrhea for several days. Lab tests revealed evidence of metabolic acidosis.
Lab Techniques
1. Melting Point
Organic molecules have unique melting points. For this to be an effective technique in identifying compounds, you need to know the melting points of the possible
unknowns. Find and write down the literature value of melting points of some common over the counter analgesics.
Fig: Melting Point Apparatus
The procedure for determining melting point will be explained in the laboratory.
2. Thin-Layer Chromatography (TLC)
Thin-layer chromatography involves spotting the sample to be analyzed near one
end of a sheet of plastic (called a plate) coated with a thin layer of an adsorbent. The plate is placed on end in a covered beaker containing a shallow layer of solvent. The solvent rises up the plastic sheet through the adsorbent by capillary action. The distance that the sample rises up the TLC plate is related to relative attractions to the solvent and to the adsorbent layer. The greater the sample is attracted to the solvent the farther it rises up the plate. Pay attention when you grab the TLC plate, hold it by the
edges to avoid finger marks.
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CHEM 1152L Lab Manual – Page 31
Why is the Cat Sick? Prelab
1. What three sets of data will you be able to use to determine which analgesic made the cat sick?
2. Look up the reported melting points for Advil, Tylenol, and aspirin (you may need to determine the chemical name of the medication to look up the melting point). 3. Find and write down the symptoms of overdose for Advil, Tylenol, and aspirin.
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CHEM 1152L Lab Manual – Page 32
Procedure
1.
Pour enough 99.5%/0.5% ethyl acetate/acetic acid solution in a 250-mL beaker to cover the bottom with a layer measuring 0.5 cm thick. Place 2 strips of filter paper in the beaker to help fill the beaker with the vapor of the solvent. Cover the beaker with aluminum foil.
2.
Make 1 mL of a 1% solution of your unknown by dissolving it in ethanol (the solution may already be prepared for you). 3.
Spot the plates approx. 1 cm from the bottom with your unknown solution and the
known solutions (ibuprofen, aspirin, and acetaminophen) using provided capillary
tubes. You will have 4 spots total on the plate and you do not want them to overlap, so space them out accordingly.
4.
Place the plate in the beaker, recover with foil, and allow the solvent to rise near to the top of the plate. Remove plate and mark the solvent front by drawing a line
with your pencil across the place where the solvent stopped.
5.
After the plate has dried, place under UV light to visualize the spots.
Fig: TLC Plate Preparation:
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CHEM 1152L Lab Manual – Page 33
Fig:
TLC Plate Result:
TLC Plate Results:
Draw a picture of your TLC plate and include a table of the calculated R
f values.
REPORT FORM: Write a formal report to reveal what made the cat sick. Use the following guidelines for the report.
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CHEM 1152L Lab Manual – Page 34
Report Guidelines
You are to write a formal report as if you are an independent laboratory that was asked to identify the analgesic that made the cat sick. You will use three pieces of evidence to identify
the unknown compound: melting point, the cat’s symptoms and TLC. You should fully address and discuss each of these key areas when reporting your findings. For the melting point you should compare your results with known melting points of the possible medications. For the TLC, you should compare the retention factor of unknown with the known medication solutions. Finally, you should compare the cat’s symptoms to known effects of the drugs. Some things to remember as you write the report. You are NOT
the owner of the
cat. or the vet. This is a formal
report so that means no first person pronouns. Do not refer to yourself, the professor, the lab or lab manual. Do not use colorful or flowery language. Do not report your opinion or feelings or thoughts. Report the results, discuss the results and draw conclusions. The evidence you collected will support/indicate or deny/reject certain identifications. The data will not unequivocally
“prove” anything. Formatting/Details
Your report is due when you come to lab next week.
Your report should be typed and double spaced.
You are allowed to attach (staple, glue or tape) figures or hand draw structures, etc.
Make sure to attach/include the photographs or chromatogram (if any) taken in lab to the
report.
Your report should have a list of references. o
I am not picky about what format you use but you should be consistent.
o
The references should be for the various tests you performed and should not include your lab manual (but may include your textbook)
o
Do not list the reference right in the text
o
You may reference Wikipedia or about.com but you must also have other more reliable sources
Your report should be organized into the following sections with clearly marked headings: Introduction, Results, Discussion, Conclusions, References
Introduction:
introduce the situation, define the problem, and the purpose of your analysis. Results:
present the results separated by the tests, namely, melting point, TLC (Rf values),
and symptoms of sick cat. Presentation of data in a table format would be clear and concise.
Do not draw conclusions or discuss what the results might mean here. Discussion:
Discuss what the results indicate. –
Discuss each set of results (melting pt., TLC, and symptoms) separately.
–
Make comparisons to the known compounds (both similarities and differences). Conclusion:
Summarize the results and identify the analgesic. No new information should be in this section. References:
Any format but consistent.
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CHEM 1152L Lab Manual – Page 35
Preparation of Acetyl Salicylic acid (Aspirin)
Introduction
Almost all the materials that we are exposed to daily are the products of chemical modifications of compounds or materials occurring naturally. In particular, the drugs that we employ in the treatment of diseases are prepared synthetically, either from scratch or by modification of naturally occurring compounds. Therefore, knowledge of the process of making new molecules (i.e., synthesis) is crucial to anyone involved in one way or another with a career in chemical and pharmaceutical sciences. Background
One of the most widely used non-prescription drugs is aspirin. In the US, more than 15000 pounds are sold each year. Aspirin, or acetylsalicylic acid, is a synthetic compound known virtually to everyone. As an example, 1 in 5 Americans take aspirin at least once a day. Aspirin is an effective analgesic (pain
killer) that can reduce the mild pain of headaches, toothache, neuralgia (nerve pain), muscle pain and joint pain (from arthritis and rheumatism). Aspirin behaves
as an antipyretic drug (it reduces fever) and an anti-inflammatory agent capable relieving the swelling and redness associated with inflammation. It is an effective agent in preventing strokes and heart attacks due to its ability to act as an anti-
coagulant.
Early studies showed the active agent that gave these properties to be salicylic acid. However, salicylic acid contains the phenolic and carboxylic acid groups. As a result, the compound was too harsh to the linings of the mouth, esophagus and stomach. The Bayer Company in Germany patented the ester and marketed as “aspirin” in 1899. It was first put to good use by Felix Hoffman, an employee of Bayer AG who gave it to his father to treat arthritic pain, because
it was much better tolerated than other salicylic acid derivatives used at the time. The acetylsalicylic acid was hydrolyzed in the small intestine to salicylic acid, which was then absorbed into the bloodstream. It's mode of action, whose discovery gave the Nobel Prize to Sir John Vane in 1970 involves the inhibition of
the synthesis of prostaglandins, molecules that cause inflammation, blood clotting, and trigger pain.
The relationship between salicylic acid and acetyl salicylic acid is shown in
the following formulas,
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CHEM 1152L Lab Manual – Page 36
Aspirin still has side effects. Hemorrhaging of the stomach walls can occur
even with normal dosages. These side effects can be reduced through the addition of coatings or through the uses of buffering agents. Magnesium hydroxide, magnesium carbonate and aluminum glycinate, when mixed into the formulation of the aspirin, reduce the irritation.
Although drug industries have developed thousands of far more complicated compounds for the treatment of numerous diseases, aspirin is still called the most successful drug in history, and it is to this day one of the products
that generates the largest revenues for pharmaceutical companies.
This experiment will acquaint you with a simple synthetic challenge in the preparation of aspirin. The method uses acetic anhydride and an acid catalyst, like sulfuric or phosphoric acid, to speed up the reaction.
The reaction is called an acetylation, because an acetyl group is being added to one of the reagents, in this case salicylic acid. This reaction belongs to a larger class of organic transformations called esterifications, because an ester of the acid (in this case acetic acid) is made by combination with an alcohol or phenol (in this case salicylic acid). The reaction is catalyzed (that means, accelerated) by an acid, which will be phosphoric acid in this case. The lab instructor will tell you about the mechanism of this reaction while the reaction is running.
If any salicylic acid remains unreacted, its presence can be detected with a 1% iron (III) chloride solution. Salicylic acid has a phenol group. The iron (III) chloride gives a violet color with any molecule which contains a phenol group. Notice that aspirin no longer has the phenol group (OH group), so a pure sample of aspirin will not give a purple color with a 1% iron (III) chloride solution.
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CHEM 1152L Lab Manual – Page 37
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CHEM 1152L Lab Manual – Page 38
Name:________________________________________________________________
Pre-lab Questions
1. Draw the structure of aspirin. Should this compound test positive with 1% iron (III) chloride solution? Explain your answer.
2. Aspirin can irritate the stomach. What is done in the formulation of the drug that reduces this side effect?
3. What is the active ingredient that gives aspirin its therapeutic properties?
4. Calculate the % yield of the reaction if 6.3 g of aspirin were obtained starting with 7.5 g of salicylic acid. You can consult your textbook chapter section 5.8 and 5.9 for this calculation.
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CHEM 1152L Lab Manual – Page 39
Procedure
Safety Precautions: Avoid coming in contact with acetic anhydride or phosphoric acid. Both compounds will produce burns. Avoid inhaling acetic anhydride vapors. Use the fume hood while adding acetic anhydride and phosphoric acid, Wear your safety goggles AT ALL TIMES
.
I. Synthesis of Aspirin
1. Prepare a bath using a 400-mL beaker filled about half-way with water. Heat to boiling.
2. Weigh out 2.0 g of salicylic acid and place it in a 125mL Erlenmeyer flask. Use this quantity of salicylic acid to calculate the theoretical or expected yield of aspirin.
3. Measure 3.0 mL of acetic anhydride with a graduated cylinder, and add them carefully to the Erlenmeyer. While swirling add 3 drops of concentrated phosphoric acid.
4. Mix the reagents and then place the flask in the boiling water bath; heat the mixture gently for 15 to 20 minutes swirling the contents from time to time.
5. After heating the mixture, let it cool to room temperature. Then, CAREFULLY pour 20
mL of ice cold water into the reaction mixture, mix thoroughly, and place the flask in an ice bath. The water destroys any unreacted acetic anhydride and will cause the insoluble aspirin to precipitate from solution as the mixture cools. If no crystals appear after 10 minutes, scratch the sides of the Erlenmeyer CAREFULLY to induce crystallization.
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CHEM 1152L Lab Manual – Page 40
6. While your flask is in the ice-bath, set up a filter flask with a Büchner funnel and a piece of moist filter paper (be sure that the paper lies flat and covers all the holes). Connect the Buchner flask to the vacuum line on your lab bench.
7. Transfer the contents of the Erlenmeyer flask to the Büchner funnel and apply vacuum suction. You have to do your best to transfer as much of the material as possible with a spatula.
8. Wash the Erlenmeyer flask with 2 to 5 mL portions of chilled water, and pour these
washes through the Büchner funnel. Wash the product in the Büchner funnel with
two additional 2 to 5 mL portions of chilled distilled water.
9. Continue suction through the Büchner funnel for 10 minutes to help dry the crystals Disconnect the suction. Carefully, transfer the crystals in a labeled vial (no cap, remember to measure the mass of empty vial) and keep it aside in an open drawer until next lab. This allows simple air drying of your synthesized product. 10. On the next lab, take the product out of the drawer and then weigh it. Calculate your
percent yield.
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CHEM 1152L Lab Manual – Page 41
Name:_______________________________________________________________
Lab Report
I. Synthesis of Aspirin
Present all your data in an organized matter (Think TABLE!)
Calculate the theoretical yield of aspirin
Calculate the % yield of your synthesis
Percent Yield calculation: Percent Yield
=
(
Actual Yield
TheoreticalYield
)
×
100
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CHEM 1152L Lab Manual – Page 42
Name:_______________________________________________________________
Post-lab Questions
1. What is the purpose of the concentrated phosphoric acid in the preparation of aspirin? Could some other acid be used, give example?
2. What would happen to your % yield if the product is not completely dry?
3. A student expected 10.0 g but obtained only 6.3 g. Comment on some possible reasons for that low %yield.
4. Tylenol is also an analgesic often taken by people who are allergic to aspirin. The active ingredient is acetaminophen.
Would acetaminophen give a positive phenol test? Explain your answer.
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CHEM 1152L Lab Manual – Page 43
Characterization and Determination of the Purity of the
Aspirin
Last week, you had synthesized acetylsalicylic acid (aspirin) in the laboratory, after calculating the percent yield of your product, in this lab, you are going to characterize and determine the purity of the aspirin you synthesized.
Introduction:
The purity of prepared aspirin can be assessed by a number of ways. One
of the ways is by utilizing a simple chemical method, the FeCl
3
method. The ferric
chloride reacts with the phenolic hydroxyl group of salicylic acid and results into the formation of purple Fe (III) complex of salicylic acid. The appearance of purple color reveals the presence of salicylic acid in the analyte. The melting point determination and thin layer chromatography can also be used to assess the purity of aspirin. The comparison of the melting points of salicylic acid with the synthesized aspirin, clearly distinguishes the formation of product from the reactant. Also, the comparison of your aspirin with the commercial one allows you to understand the effect of impurities on melting point determination. Method 1. FeCl
3
method
1. The aspirin you prepared is not pure enough for use as a drug and is not
suitable for ingestion. The purity of the sample will be tested with 1% iron (III) chloride solution and compared with a commercial aspirin and salicylic acid.
2. Label three test tubes 1, 2, and 3; place a few crystals of salicylic acid in tube #1, a small sample of your aspirin into tube #2 and a small sample of crushed commercial aspirin into tube #3. Add 5 mL of distilled water to each test tube and swirl to dissolve the crystals.
3. Add 10 drops of 1% iron (III) chloride to each test tube.
4. Compare and record your observations. The formation of a purple color indicates the presence of salicylic acid. The intensity of the color qualitatively tells how much salicylic acid is present.
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CHEM 1152L Lab Manual – Page 44
Method 2. Melting Point Method
The procedure for determining melting point will be explained in the laboratory.
1. Determine the melting points of salicylic acid, synthesized aspirin, and commercial aspirin. Record your observation.
Method 3. Thin Layer Chromatography Method Pay attention to correctly grab the TLC plate, hold it by the edges to avoid finger marks. Make sure not to scratch the silica coat with your fingernails.
In order to develop a TLC plate, 6.
Pour enough 99.5%/0.5% ethyl acetate/acetic acid solution in a 250-mL beaker to cover the bottom with a layer measuring 0.5 cm thick. Place 2 strips of filter paper in the beaker to help fill the beaker with the vapor of the solvent. Cover the beaker with aluminum foil.
7.
Hold the TLC plate on the edges so that coated surface does not get scratched.
8.
Draw an origin line along the short side
1.5 cm from the bottom. 9.
Make 1 mL of a 1% solution of your crude aspirin by dissolving it in ethanol. 10.
Get 1% salicylic acid in ethanol, and 1 % commercial aspirin in ethanol from the instructor. 11.
Spot the TLC plate 1 cm from the bottom with your crude aspirin solution, salicylic solution, and commercial aspirin solution using the thin capillary tubes. 12.
Place the plate in the beaker and allow the solvent to rise near to the top of the plate. Remove plate and mark the solvent front.
13.
After the plate has dried, place under UV light to visualize the spots.
14.
Mark the spots.
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CHEM 1152L Lab Manual – Page 45
15.
Calculate Rf values. DATA:
Table 1: FeCl
3
Reaction Observation Table
Test tube #
Sample
Color
Intensity
1
Salicylic acid
2
Your aspirin
3
Commercial aspirin
Table 2. Melting Point Determination method
Substance
Trial 1
Salicylic acid
Synthesized aspirin
Commercial aspirin
Table 3. TLC plate method
Distance (cm)
Rf
solvent
Salicylic acid
Synthesized aspirin
Commercial Aspirin
Rf calculation:
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CHEM 1152L Lab Manual – Page 46
Post Lab Questions
1. Compare the melting point of synthesized aspirin with the commercial aspirin and literature value of melting point of aspirin? Comment on your comparison, why the difference?
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CHEM 1152L Lab Manual – Page 47
Preparation of Soap
Background
Read Section 17.6 C and Section 19.5 B of your textbook for understanding soap synthesis reaction and how does soap work. Make sure that your research is thorough enough for you to be able to answer the prelab and postlab questions.
Objective
To make a soap and study its properties.
Procedure
Measure 23 mL of vegetable oil into a 250-mL Erlenmeyer flask. Add 20 mL of ethyl alcohol and 20 mL of 25% NaOH solution. While stirring the mixture constantly with a glass rod, heat the flask and its contents in a boiling water bath.
After heating for about 20 minutes, the odor of the alcohol will disappear, indicating that the reaction is complete. A pasty mass containing a mixture of soap, glycerol and unreacted NaOH is obtained. Use an ice-water bath to cool the flask. To precipitate or “salt out” the soap, add 150 mL of saturated NaCl solution to the soap mixture while stirring vigorously. This process increases the density of the solution, the soap will float on top of the aqueous solution. Filter the precipitate using the apparatus shown below and wash the soap with 10 mL of ice cold water. Observe the appearance of your soap and record your observations.
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CHEM 1152L Lab Manual – Page 48
You can bring any essential oil you wish to perfume your soap with or molds to form the soap so you can use it later.
You will also be asked to investigate some properties of soap and we will give you the procedure for those:
Emulsifying Properties:
Shake 5 drops of vegetable oil in a test tube containing 5 mL of water. A temporary emulsion of tiny oil droplets in water will be formed. Repeat the same test, but this time add a small piece of the soap you have prepared before shaking. Allow both solutions to stand for a short time. Compare the appearance and the relative stability of the two emulsions.
Hard Water Reactions:
Place about one-third spatula full of the soap you have prepared in a 50-mL beaker containing 25 mL of water. Warm the beaker to dissolve the
soap. Pour 5 mL of the soap solution into each of 5 test tubes and add the solutions according to the following table:
test tube
add
1
2 drops 5% CaCl
2
2
2 drops 5% MgCl
2
3
2 drops 5% FeCl
3
4
tap water
Use test tube 5 for the alkalinity of your soap. Write what you observed in each case.
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CHEM 1152L Lab Manual – Page 49
Prelab Questions – Soap
Name: 1.
Define the following terms:
a.
hydrophobic
b.
hydrophilic
c.
emulsifying agent
d.
saponification
2.
What is the most common fatty acid in coconut oil? If you made some soap using coconut oil what is the formula for the most abundant soap you will make?
3.
How would you convert a soap back to its fatty acid?
4.
What is an average pH for soap?
5.
What is hard water?
6.
Steric acid is insoluble in water while sodium stearate (soap) is soluble. What causes the difference in solubility? Explain using the formulas for both compounds.
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CHEM 1152L Lab Manual – Page 50
Name:________________________________________________________
Report
Preparation
Appearance of your soap:
Properties:
Emulsifying Properties
Which mixture, oil-water or oil-water soap, forms a more stable emulsion?
Hard Water Reaction Observation
Test tube 1 + CaCl
2
______________________________________________________
Test tube 2 + MgCl
2
______________________________________________________
Test tube 3 + FeCl
3
______________________________________________________
Test tube 4 + tap water___________________________________________________
Alkalinity
pH of your soap solution (test tube 5) _______________________________________
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CHEM 1152L Lab Manual – Page 51
Post-Lab Questions
1. When you made soap, first you dissolved vegetable oil in ethanol. What happened to the ethanol during the reaction?
2. List two advantages and two disadvantages of soaps versus detergents?
3. Soaps that have a pH above 8.0 tend to irritate some sensitive skins. Was your soap good enough to compete with commercial preparations?
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CHEM 1152L Lab Manual – Page 52
Oxidation Lab – Pre-lab
In organic chemistry, we learn about oxidation reactions occurring with certain types of functional groups (i.e. alcohols and aldehydes). When oxidation of a primary alcohol occurs, the expected product is an aldehyde, which will then be further oxidized to a carboxylic acid. When a secondary alcohol is oxidized, the product will be a ketone. If an aldehyde is oxidized, it will convert to a carboxylic acid. Ketones and tertiary alcohols, however, cannot be oxidized any further and will be the end product of a secondary alcohol oxidation.
Using different reaction conditions can affect the type of oxidation products obtained. For example, chromic acid is a strong oxidizing agent, so it will oxidize indiscriminately. However, when Tollens’ reagent is used, only aldehydes are able to be oxidized.
In this lab, you will be given three compounds labeled A, B, and C. You will conduct tests to determine the identity of compounds A, B, and C. The compounds used in this lab are 2-butanol, benzaldehyde, and cyclohexanone. Based on your knowledge of oxidation reactions and the data collected from the tests, you should be able to determine which unknown is which chemical.
For each of the compounds that you will be working with, draw the structure, label the functional group present, and determine for which chemical tests listed in the procedure you would expect to see a positive result. A) 2-butanol
B) benzaldehyde
C) cyclohexanone
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CHEM 1152L Lab Manual – Page 53
Oxidation Lab – Procedure
You will need to perform the chromic acid test and the Tollens’ test on all the unknown compounds. A known compound that will test positive for each test will also be provided. It is advisable to perform each test on the known compound that will test positive so that you have a comparison point.
Chromic Acid Test
The chromic acid test is useful for distinguishing primary and secondary alcohols and aldehydes from ketones and tertiary alcohols. Primary and secondary alcohols and aldehydes will react with chromic acid and become oxidized. The evidence of a reaction
is the loss of the brown-red color of the chromic acid and the appearance of a blue-
green solution. Ketones cannot be oxidized. Nevertheless, if you heat your sample at too high of a temperature and for too long you may get ambiguous results. To perform the chromic acid test: 1.
Put 5 drops of the sample being tested in a test tube. 2.
Add 10 drops of acetone and 2 drops of chromic acid reagent. 3.
Warm mixture in a 60
C hot water bath for 5-10 minutes. Record your observations.
When you have completed this test put all chemicals in the: Heavy Metal Waste
Tollens’ Test
Tollens’ test is a test for aldehydes. Alcohols and ketones will not react. The evidence of the reaction occurring (a positive test) is the formation of a silver mirror on the test tube.
First, you need to make the Tollens’ reagent
. 1.
In a small beaker mix 10 drops of Tollens’ solution A (10% AgNO
3
) with 10 drops of Tollens’ solution B (10% NaOH). This will yield a dirty brown precipitate, AgOH. 2.
Dissolve the precipitate by adding 10% ammonia drop by drop. Be careful that you
do not add too much ammonia. 3.
Put 5 drops of the sample being tested in a clean test tube that you obtain from your instructor.
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CHEM 1152L Lab Manual – Page 54
4.
Divide equally the Tollens’ reagent that you just made into the test tubes. 5.
Mix gently and then let the test tubes stand for 10-15 minutes. Record your observations. When you have completed this test put all chemicals in the: Heavy Metal Waste
Data
Organize your data into the tables provided.
Chromic Acid Test results
Chemical
Appearance
+/- result
Unknown A
Unknown B
Unknown C
Tollens’ Test results
Chemical
Appearance
+/- result
Unknown A
Unknown B
Unknown C
Identity of Unknowns:
Unknown
Compound Name
A
B
C
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CHEM 1152L Lab Manual – Page 55
Post-lab
Now that you have identified the unknowns, for any compound that had a positive test (e.g gave the expected result if oxidation reaction occurred), write the complete reaction
(reactants and products).
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CHEM 1152L Lab Manual – Page 56
Polymers
Prelab
Name: 1.
Define the following terms:
a. monomer
b. polymer
c. macromolecule
d. copolymer
e. thermosetting polymer
f. thermoplastic polymer
g. condensation polymer
h. addition polymer
2. List some general properties of all polymers.
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CHEM 1152L Lab Manual – Page 57
Polymers
1,2
Objective:
The objective of this experiment is to explore the change in physical properties as a result of cross-linking polymers. In this experiment you will also produce a condensation
polymer. Background Information
Polymers are large molecules that consist of small repeating units called monomers connected by covalent bonds. Polymers can be natural or synthetic. Examples of natural polymers are shellac, amber, cellulose and proteins. In the past hundred years, the plastics industry has made synthetic polymers that are in many of the materials we use everyday, such as carpeting, plastic wrap, nonstick pans, and plastic cups. In medicine, synthetic polymers are used to replace diseased or damaged body parts such
as hip joints, teeth and heart valves. An addition polymer is a polymer which is formed by an addition reaction, where many monomers bond together via rearrangement of bonds without the loss of any atom or molecule. This is in contrast to a condensation polymer which is formed by a condensation reaction where a molecule, usually water, is lost during the formation.The properties of a polymer depend on a number of factors, such as: monomer identity, chain linearity, chain length, chain branching, degree of cross-linking, and use of plasticizers. Cross linking tends to increase strength and toughness. Chemistry of Slime:
Cross linking consists of the formation of chemical bonds between
chains. Among other applications, this process is used to strengthen rubbers in a process known as Vulcanization, which is based on cross linking by sulfur. Car tires, for example, are highly cross linked in order to reduce the leaking of air out of the tire and to toughen the tires durability. Eraser rubber, on the other hand, is not cross linked to allow flaking of the rubber and prevent damage to the paper. The chemistry by which a cross-linked polymer gel is produced from linear polymer molecules has a straightforward explanation. The polymer used is "poly (vinyl alcohol)". The monomer has a formula of: Borax is sodium borate, Na
3
BO
3
. The borax actually dissolves to form boric acid, H
3
BO
3
.
This boric acid-borate solution is a buffer with a pH of about 9 (basic). Boric acid will accept a hydroxide OH
-
from water as indicated below. 1
E.Z. Casassa, A. M. Sarquis, C. H. Van Dyke, J. Chem. Ed.
, 1986, 63, 57 – 60
2
T. I. Bieber, J. Chem. Ed.
, 1979, 56, 409 – 410
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CHEM 1152L Lab Manual – Page 58
The hydrolyzed molecule will then act in a condensation reaction with PVA. In the above reaction, two PVA molecules are shown being cross-linked by a hydrated borax molecule. Four molecules of water are also produced. The resulting material is about 95% water. It is the water that gives the polymer flexibility. Note that as the polymer dries it returns to its solid phase now as a sheet that is rigid and almost transparent. The PVA does not dissolve easily in water. Guar Gum dissolves in water much more easily than PVA, but seems to "jell" at a much more unpredictable rate than the PVA mixture does. For this reason, PVA is preferred. Procedure
Slime:
Measure 40 ml of polyvinyl alcohol (PVA) and transfer to a beaker. Add food coloring to the PVA (food coloring gives a very intense color, use very
small amounts). Add 10 ml of sodium borate (different measuring device). Mix and stir until completely gelled. Record your observations while stirring. After it completely gelled, record your observations while pressing on the gel, while stretching the slime slowly and fast. Feel free to add more PVA or sodium borate and observe the changes. Place a small amount of the gel in a paper towel to dry overnight and record your observations. The slime is non toxic and is safe to handle, so you can put it in a Zip-lock bag and seal it to take home.
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CHEM 1152L Lab Manual – Page 59
Chemistry of Nylon 6,6:
Nylon 6,6 is made of hexamethylene diamine and adipic acid, which give nylon 6,6 a total of 12 carbon atoms, and its name.
The reaction can be written as,
Nylon-6,6 is semicrystalline polyamide commonly used in fiber applications such as carpeting, clothing, and tire cord. It is also used as an engineering material in bearings and gears due to its good abrasion resistance and self-lubricating properties. Nylon 6,6's longer molecular chain and denser structure qualifies it as a premium nylon fiber, specified most often by professional architects and designers for use in commercial settings like offices, airports, and other places that get a lot of wear and tear. It is also an excellent choice for residential carpet applications where it is available under the Wear-Dated carpet fiber brand name, as well as StainMaster.
Procedure
Nylon 6,6: Your instructor may demonstrate Nylon 6,6 synthesis using commercial premixed reagents. Or,
Prepare a 5% aqueous solution of hexamethylenediamine (1,6-hexanediamine). Pour 10 mL of that solution into a 50 mL beaker. Add 10 drops of 20% sodium hydroxide solution. Carefully add 10 mL of a 5% solution of adipoyl chloride (dissolved in cyclohexane solvent!) to the hexamethylenediamine by pouring it down the inside wall of the slightly tilted beaker. Two layers will form, and there will be an immediate formation of a polymer film at the liquid-liquid interface. Using a copper-wire hook (a 6-
inch piece of wire bent at one end), gently free the walls of the beaker from the polymer strings. Then hook the mass at the center and slowly raise the wire so that polyamide forms continuously, producing a rope that can be drawn out for many feet. The strand can be broken by pulling it faster. Rinse the rope several times with water and lay it on a
paper towel to dry. With the piece of wire, vigorously stir the remainder of the two-phase
system to form additional polymer. Decant the liquid and wash the polymer thoroughly with water. Allow the polymer to dry. Do
NOT
discard the nylon in the sink. Use a waste container.
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CHEM 1152L Lab Manual – Page 60
Observations
Preparation of Slime:
PVA before the sodium borate is added: PVA after the sodium borate is added: Stretching the cross-linked PVA slowly
:
Stretching the cross-linked PVA rapidly
:
Observation of the cross-linked PVA left out in the air overnight: Preparation of Nylon:
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CHEM 1152L Lab Manual – Page 61
Household Chemicals Assignment
You have learned about several different functional groups within organic chemistry since the beginning of the semester. This assignment will now ask you to use your knowledge of organic chemistry and naming of functional groups. What you will need to do for this week’s assignment is find products in your home (in the kitchen, the laundry room, the bathroom, medicine cabinet, etc.) that contain different types of organic molecules. For each functional group listed, you need to find two different products that contain a compound with that functional group. For example, in your lotion you might see “cetyl alcohol” listed. This is a type of alcohol. You would list the name, draw the structure, and give the name of the product in which you found that compound. You would then need to find a second product containing a different
alcohol and list that as well. If you feel like you are having trouble finding items around your house, a quick trip to the grocery store or pharmacy might help.
When you have finished, answer the questions below and turn all pages of this assignment in for full credit.
The table provided on the following pages gives you space to record all your findings.. Questions
After doing this assignment, were you surprised at how many chemicals you found in your everyday products? Having learned the nomenclature rules for the various functional groups, did you find it easier to identify what functional groups were in the ingredients listed on your household products?
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CHEM 1152L Lab Manual – Page 62
Household Chemicals
Functional Group
Compound Name
Name of
Household
Product
Structure
Alcohol
Ether
Carboxylic
Acid/Carboxylate
Ester
Ketone
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CHEM 1152L Lab Manual – Page 63
Household Chemicals
Functional Group
Compound Name
Name of
Household
Product
Structure
Aldehyde
Amine/
Ammonium Salt
Aromatic
(benzene ring)
compound
Thiols or Sulfides
Hydrocarbons
(indicate if
saturated or
unsaturated)
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CHEM 1152L Lab Manual – Page 64
Lipids Lab
3
We encounter lipids on a daily basis, in particular when we step into the kitchen. Edible fats and oils are triglycerides that are solids or liquids at room temperature, respectively.
Sometime in the early 2000’s, “trans fats” and foods such as margarine came under scrutiny because of their potential bad effects on health. The FDA now requires that the food label includes trans fat content, and some labels you read may even specify the amount of monounsaturated, saturated, and polyunsaturated fats present in the food.
4
Triglycerides, or triacylglycerols, are compounds that have a glycerol backbone, with three fatty acids connected through esterification. Triacylglycerols can be simple or mixed, with 3 fatty acids that are the same or a mix of 2 or 3 fatty acids, respectively. Unsaturated fats are those that contain some amount double bonds in the fatty acid chains. A monounsaturated fatty acid is one where triacylglycerol contains only one double bond, while a polyunsaturated fats contain more than one double bond. We have
learned that double bonds can be cis
or trans
. Typically, in natural oils or fats, the double bonds will be in the cis configuration. This impacts the packing ability of the compound and the “kinks” in the fatty acid chains lead to compounds that are liquid (oil) not solid (fat). From a health perspective, saturated fats (e.g. lard) and unsaturated trans
-
triacylglycerols (e.g. margarine) appear to be linked to an increase incidence of things like heart disease and higher “bad” cholesterol (LDL), which is why the FDA requires this information to be disclosed on packaging, in order to help people avoid high intake of these unhealthy fats. Peroxides are a type of chemical compound that contain oxygen-oxygen single bonds. Peroxides degrade oil, especially something like olive oil, affecting shelf-life and 3
Making Sense of Olive Oil: Simple Experiments To Connect Sensory Observations with the Underlying Chemistry, Richard A. Blatchly, Zeynep Delen, and Patricia B. O’Hara, Journal of Chemical Education
2014
91
(10), 1623-1630
4
NMR and IR Spectroscopy for the Structural Characterization of Edible Fats and Oils. An Instrumental Analysis Laboratory
J. Chem. Educ.
2008
, 85, 11, 1550
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CHEM 1152L Lab Manual – Page 65
eventually taste of the oil. Peroxides will oxidize double bonds present in an oil, so this would have a large effect on unsaturated triacylglycerols. Finally, antioxidants are compounds that are found in natural products or can be added to scavenge any free radicals (which lead to oxidation and subsequent issues as noted above). Tests can be performed to identify the presence of antioxidants in oils.
The following experiments are designed to allow you to explore some of the properties of various edible oils and connect the chemical concepts learned in lecture to their application.
Procedure
Obtain samples of the two types of olive oil (one is extra virgin olive oil (EVOO), the other is not), vegetable oil (which is, in our case, soybean oil), canola oil, and coconut oil. You will need to make a warm water bath and gently heat the coconut oil so that it melts into a liquid that you can work with. For all the following tests, perform them on all four types of olive oil and record your data
neatly in the tables provided. You may perform the tests in any order except you must start with the Test for Unsaturation first, as it has to sit for 1 hour. You will need a test tube rack with several test tubes to carry out these tests.
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CHEM 1152L Lab Manual – Page 66
Unsaturation: Iodine Test for Double Bonds
The iodide test can be used to test for the presence of double bonds. If a compound has
double bonds, the purple color of iodine will disappear and the solution will become a brown-to-orange color. Add two drops of iodine solution to each oil and mix well. Note the initial color observed upon mixing. After an hour, note the color again. EVOO
Olive Oil
Vegetable
Oil
Canola Oil
Coconut
Oil
Observations immediately after mixing the iodine and
oil
Observations after 60 minutes
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CHEM 1152L Lab Manual – Page 67
Free Fatty Acid Detection with Alizarin Yellow
When equal amounts of oil and Standard Base are mixed, no color change will be observed if the free fatty acid (FFA) content is less than 0.8%. If the indicator changes colors, the sample has “failed” the FFA test and has higher than 0.8% FFA. The standard base solution is an aqueous solution that you will be adding to an oil.
Add 10 drops of the base solution containing the indicator to 10 drops of oil in a test tube without mixing. Note what happens. Mix well, then note what happens.
Record the color and concentration of the base solution: _________________________
EVOO
Olive Oil
Vegetable
Oil
Canola Oil
Coconut
Oil
Observations when alizarin yellow is first added
Observations after the solution is mixed
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CHEM 1152L Lab Manual – Page 68
Peroxide Test
Ideally, peroxide levels in any oil should be low, as these will cause oxidation of any unsaturated bonds and will change the profile of the oil. You will use commercially available test strips to measure the peroxide content.
Locate the peroxide test strips. Dip a test strip into a small sample of oil. Then add a small drop of water to the strip. Wait 15 to 30 seconds, then note the color. Use the color chart on the test strip container to record the amount of peroxides on the sample, being sure to include units!
EVOO
Olive Oil
Vegetable
Oil
Canola
Oil
Coconut Oil
Observation
s from oil on strip, then change once
adding H
2
O
Amount of peroxide in the sample
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CHEM 1152L Lab Manual – Page 69
Antioxidant Test
When the iron reagents are mixed with the oil, antioxidants present in the oil will reduce the iron. If that occurs, a bright blue color (Prussian blue) will develop in a short amount of time (seconds to a minute). Add 2 drops of the iron chloride solution and 20 drops of the potassium ferricyanide solution to a small test tube and mix it. What color is this solution? _____________
Add 10 drops of oil to the solution without mixing it. Observe what happens, then mix the solution and make observations again about the solution.
EVOO
Olive Oil
Vegetable
Oil
Canola
Oil
Coconut Oil
Observation
s when olive oil is first added to iron
solution
Observation
s after solution is mixed and time elapses
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CHEM 1152L Lab Manual – Page 70
Lipids Lab – Post-lab
1. Which oils contained saturated fats? Which oils contained unsaturated fats? How do you know?
2. Looking at the data from your FFA tests, did any oil “pass” the test? Which one(s)? 3. Why do two phases form in the FFA tests? Does the standard base solution stay on top or go to the bottom of the tube? Why must you mix the solutions together in order for the test to work?
4. Did any of the oils tested have a significantly higher level of peroxides compared to the other samples? What might you conclude about a sample that did test higher for peroxide content?
5. Which oils tested “positive” for antioxidants? Look up what types of chemical compounds/structures are typically considered to have antioxidative properties and determine if those kinds of structures are common in the types of oils you found to have antioxidant content.
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CHEM 1152L Lab Manual – Page 71
1Protein Lab
1,2
Proteins are an essential part of the human body, making up almost 50% of dry weight and performing myriad roles throughout the body. Proteins are made when amide bonds form between smaller compounds called amino acids. The sequence of amino acids that make up any given protein is known as the protein’s primary structure
. Regions of a protein then can assemble based on hydrogen-bond interactions to form structures such as a
-helices and b
-pleated sheets. This is what is known as secondary
structure
. Finally, the entire peptide chain folds into a three-dimensional shape that correlates directly to the types of interactions that occur between the “R” groups in the amino acids. These interactions include intermolecular forces such as London dispersion forces and hydrogen bonding, and other interactions such as electrostatic attraction. This tertiary structure
is crucial to the proper functioning of the protein; in many diseases, replacement of one amino acid reside can have detrimental effects on the proper folding of the protein, changing the protein’s function. Some proteins also have quaternary structure
. This occurs when two or more folded polypeptide chains come together to form a complex. An example of a protein with quaternary structure is hemoglobin, found in red blood cells. Hemoglobin is a globular protein that contains two a
and two b
units, and is responsible for oxygen transport throughout the body. Hemoglobin contains another type of unit called heme. Heme is an
organic complex that contains Fe
2+
which binds oxygen, allowing hemoglobin to act as an oxygen transport protein.
Similar to hemoglobin, myoglobin (Mb) (shown below) incorporates a heme group for binding oxygen. Myoglobin is found primarily in the cardiac and also skeletal muscle. Mb is responsible for storing oxygen until it is needed. In the body, Mb exists in a form called Oxy-Mb, where the O
2
is bound to the protein and the heme group. Once the protein is removed from a living system, Mb converts to a form called Met-Mb, where the oxygen molecule is released and a water molecule instead becomes bound to the protein. Figure 1. Myoglobin. Protein Databank. https://www.rcsb.org/3d-view/1MBN
___________________________________________________________________________________________________________________________________
1
Adapted from “Microburger Biochemistry: Extraction and Spectral Characterization of Myoglobin from Hamburger,” S. Bylkas and L. Andersson, J. Chem. Ed
, 1997. 2
UKEssays. (November 2018). Protein Denaturation of Egg White and Milk: Experiment.
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CHEM 1152L Lab Manual – Page 72
When proteins are broken down and lose their 3-D structure, the process is called denaturation. Denaturation will result in a loss of every protein structure except for the primary structure. There are numerous ways in which a protein may be denatured. Heat, agitation, changes in pH, along with addition of metal ions and/or organic compounds can all be used as mechanisms of denaturation. Sometimes, denaturation may be desired, for example, when medical equipment is autoclaved, the heat and steam will denature the proteins of harmful bacteria. On the other hand, if you wanted to
study a protein in lab in its natural form, you would have to be very careful in handling the protein, so that it wouldn’t become denatured.
McGraw Hill Publishing.
In this lab, you will explore several facets of proteins and denaturation by working with common grocery items: ground beef and eggs.
Procedure
Myoglobin extraction
1. Start with your 8 g “microburger” by putting it in a 15-mL plastic centrifuge tube. Using
0.10 M sodium phosphate at pH=7 as a buffer, add enough solution to reach the 10-mL mark on the centrifuge tube. 2. Using a glass stir rod, agitate the mixture to help break open the cells. Do this for a minute, being careful not to stir so hard that mixture comes out of the tube. 3. Add more buffer to the centrifuge tube so that the volume is at 15 mL. 4. Label your sample, then place it in the centrifuge. The centrifuge has to run for 15 minutes, so we will collect several student samples before starting the centrifuge. Your lab instructor or TA will show you how to properly put your tube in and will decide when to turn it on. The centrifuge will be set to run at a speed of 10,000 rpm for 15 minutes.
While your sample is centrifuging, you can explore egg protein denaturation.
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CHEM 1152L Lab Manual – Page 73
Mb Spectroscopy
Collect your sample from the centrifuge. You should see a whitish-gray pellet at the bottom of the tube and a reddish supernatant (liquid) above it. You may also see a third layer at the top; this is fat and you want to discard this portion of the sample. The reddish supernatant should be pipetted out and transferred to another centrifuge tube. Sample Preparation
To prepare a sample for the UV-vis, dilute 1.0 mL of supernatant with 3.0 mL of sodium phosphate buffer. Use a Spec 20 UV-vis spectrophotometer to collect data. You will need to connect it to the laptop and open the UV-vis software. Allow the lamp to warm up for 5 minutes before collecting any samples. Prepare a cuvette with buffer only. Use this as the blank for the spectrophotometer. After collecting the blank, put your supernatant solution into the cuvette and allow it to collect the full spectrum. Record the absorption values found at the following wavelengths (see Table 1 in Data Section for more information): 635 nm, 580 nm, 542 nm, and 505 nm. Next, split your supernatant solution into two test tubes. In one test tube, add a small spatula tip of potassium ferricyanide crystals (K
6
[Fe(CN)]
6
). This will oxidize any Fe
2+ ions to Fe
3+
(converting Oxy-Mb to Met-Mb). Mix thoroughly then allow the solution to sit
for 5 minutes. In the other test tube, add a small spatula tip of sodium dithionite (Na
2
S
2
O
4
) to the solution. This will reduce any Fe
3+ ions to Fe
2+
(converting Met-Mb to Oxy-Mb).Mix thoroughly then allow the solution to sit for 5 minutes.
Put these solutions in a cuvette and collect the full spectrum, recording absorbance at the same wavelengths previously used. If you do not have any absorbance at a given wavelength, be sure to indicate that.
Egg Protein Denaturation
Obtain a centrifuge tube of egg white from your instructor. Pipet 1 mL aliquots of the egg white into 4 test tubes and prepare according to Table 4. Be sure to mix each solution together thoroughly and wait at least 5 minutes to observe any changes to appearance.
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CHEM 1152L Lab Manual – Page 74
Data
Table 1. Absorbance data collected for extracted Mb.
Wavelength (nm)
Absorbance (AU)
Mb Complex detected at wavelength
635
Met-Mb
580
Oxy-Mb
542
Oxy-Mb
504
Met-Mb
Table 2. Absorbance data for extracted Mb + potassium ferricyanide
Wavelength (nm)
Absorbance (AU)
635
580
542
504
Table 3. Absorbance data for extracted Mb + sodium dithionite Wavelength (nm)
Absorbance (AU)
635
580
542
504
Table 4. Denaturation of Egg Whites
Sample
Visual Appearance
Denaturation Type
Tube 1 (egg white in hot water bath at 80°C)
Tube 2 (egg white stirred vigorously for 5 minutes)
Tube 3 (egg white + 20 drops of 1M acetic acid) Tube 4 (egg white + 20 drops of saturated NaCl)
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CHEM 1152L Lab Manual – Page 75
Protein Lab Post-lab
1. Based on data collected from your initial protein extraction (Table 1), what can you say about the makeup of the protein in relationship to the two complexes? What do you observe about the mix of Mb complexes when you add the reducing and oxidizing agents (look at Tables 2 and 3)?
2. Based on your observations with the egg white, how could you tell if the protein was being denatured? What type of interactions in the secondary and tertiary structure may have been disrupted by the addition of acetic acid? By NaCl?
3. Find one other example of something done in cooking/baking that is related to either intentional denaturation of a protein or to prevent denaturation during the baking process.
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CHEM 1152L Lab Manual – Page 76
1Working with Enzymes – Lactase
Pre-Lab
1.
What are the factors that affect enzyme activity?
2.
Write the reaction for the hydrolysis of lactose. What enzyme catalyzes that reaction?
3.
Hypotheses: For the conditions listed in the table below, determine whether you would expect a positive (+) result (i.e. a significant glucose reading) or a negative
(-) result (i.e. no glucose response/reading). Test Conditions
Predicted Result ( + or -)
Lactose + Lactase, pH = 4
Lactose + Lactase, pH = 7
Lactose + Lactase, pH = 10
Lactose + Lactase, 0°C
Lactose + Lactase, 45°C
Lactose + Lactase, 100°C
Lactose + Lactase
Sucrose + Lactase
Maltose + Lactase
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CHEM 1152L Lab Manual – Page 77
1Working with Enzymes – Lactase
5
Background Information
As a catalyst, an enzyme increases the rate of a reaction by changing the way a reaction takes place, but is itself not changed at the end of a reaction. An uncatalyzed reaction in a cell may take place eventually, but not at a rate fast enough for survival. Chemical reactions in our body must occur at incredibly fast rates under mild conditions such as pH 7.4 and body temperature of 37ºC. Nearly all the chemical reactions that take place in our body are catalyzed by enzymes. The factors that affect enzyme activity
are temperature, pH, substrate concentration and the presence of enzyme inhibitors (molecules that cause the enzyme to lose its catalytic activity either by blocking the active site of the enzyme or by biding to another site on the enzyme distorting the shape
of the active site).
Lactase is the enzyme responsible for digestion of milk sugar in our bodies. It is a
hydrolytic enzyme which breaks down the disaccharide lactose into its monosaccharide components — galactose and glucose. The lack of this enzyme in the digestive tract leads to a disorder known as lactose intolerance
, a medical condition characterized by
the onset of abdominal cramps and diarrhea following ingestion of foodstuffs containing lactose. This condition is virtually nonexistent among infants, but for reasons not entirely
clear to medical science, becomes more prevalent after childhood. People who suffer from this condition must refrain from the consumption of dairy products or take dietary supplements of the missing enzyme in order to digest the lactose present in these foods.
The digestive enzymes of the human body are distributed throughout the digestive tract. A few, like amylase, are located in the mouth, a region of neutral pH; some are located in the stomach, a region of acidic pH, ~1.0; some are located in the first few inches of the small intestine, a region of near neutral pH, ~6 - 7; and some are located further along in the intestines, a region of slightly basic pH, ~8. By varying the pH of your test solutions to include pH=1, 7, & 8, you should be able to determine if lactase is located in the stomach, duodenum (beginning of small intestine), or further along in the intestines.
Introduction
In this experiment you will monitor the action of the enzyme lactase while varying
the conditions of pH, temperature, and substrate identity. Lactase catalyzes the hydrolysis of lactose, a disaccharide, into its two component monosaccharides: glucose and galactose. You will follow the activity of the enzyme by measuring the amount of glucose formed; the greater the amount of glucose present, the higher the activity of the
lactase enzyme. Test strips which resemble Litmus or pH paper, are sold commercially to assist people with diabetes in monitoring the levels of glucose in their urine. You will use these strips and record the concentration of glucose by matching the color of the strip to the color key on the side of the bottle.
5
Tammy J. Melton, J. Chem. Ed.
, 2001, 78, 1243
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CHEM 1152L Lab Manual – Page 78
Experimental
Preparation of Solutions:
1.
Prepare a lactase solution by crushing a lactase tablet using a mortar and pestle. Add about 10 mL of distilled water and mix vigorously. Filter out any solids and save
the solution into a beaker, which you should label “lactase.” Add approximately 40 mL of distilled water to the lactase solution.
2.
Prepare 1 % solutions of the sugars lactose, sucrose, and maltose by dissolving 1 g of the solid in 100 mL of distilled water. (These solutions may be prepared for you.) Label them. (CAUTION! Do not confuse the sugar lact
ose
with the enzyme lact
ase
.)
3.
For each trial of the following tests, use 10 mL of the sugar solution and 1 mL of the enzyme solution. Except for the pH trials, no additional buffering agents will be required. 4.
After 15 minutes, check the concentration of glucose with the glucose test strips by dipping a glass rod into the solution and touching the test strip. You may wish to record the times of mixing to help you know when to make the measurement. Unless otherwise instructed, you may discard the used solutions down with drain with plenty of water, and the used test strips may be placed in the trash.
pH Dependence
– Buffer solutions (at least three different ones). 1.
Place 1 mL of each buffer solution in separate beakers. 2.
Add 10 mL of the lactose solution and mix. Lastly add 1 mL of the lactase solution and mix well. 3.
Begin timing when all beakers have had the lactase added. Read and record the glucose concentration after 15 minutes. Temperature Dependence
1.
Place the lactose and lactase solutions in separate test tubes
into an ice water bath to chill. Allow them to cool to the temperature of the ice bath. Record the temperature. 2.
Mix the sugar and the enzyme together and return the test tube to the ice water bath. Read and record the glucose concentration after 15 minutes.
3.
Repeat the procedure with a warm water bath at about 45ºC. Record the glucose concentration after 15 minutes. Record the actual temperature of the solutions.
4.
Finally, place the lactase solution (only the enzyme, not the sugar) in a boiling
water
bath and leave it there for a minimum of 10 minutes. Remove it, cool, and add the enzyme to a lactose solution. Record the glucose concentration after 15 minutes.
Substrate Specificity
Test the lactose, maltose, and sucrose solutions separately at room temperature. For each separate test tube of sugar solution, add the lactase and then measure and
record the glucose concentration in all solutions after 15 minutes.
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CHEM 1152L Lab Manual – Page 79
Data:
record all your data in an appropriate format (think TABLE)
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CHEM 1152L Lab Manual – Page 80
Post-Lab Questions:
1.
At what pH does lactase present the highest enzymatic activity? In which part of the digestive tract will lactase be most effective?
2.
What is the effect of varying temperature on the activity of the enzyme? At what temperature is there the highest enzyme activity? Is it a reasonable temperature when dealing with the human body?
3.
What effect does lactase have on maltose and sucrose? Explain based on the type of glycosidic bond present on each disaccharide.
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