Lab 1 Safety and Measurements1
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Lone Star College System, Woodlands *
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1402
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Chemistry
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Feb 20, 2024
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15
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Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu I. Objectives •
To learn about safety rules followed in chemistry laboratories.
•
To learn to measure correctly using various measuring tools in the lab and to record those measurements using the correct number of decimal places and units. •
To determine number of significant figures in a measurement. II.
Introduction Part 1: Safety_______________________________________________________________________ Chemical laboratory classes can include hands-on, inquiry-based investigations. Some secondary-level laboratory activities involve the use of chemicals or equipment that poses a health or safety danger to students and instructors if not handled properly. The following rules describe how to ensure a safer and healthier environment in our classrooms and laboratories. Please read these rules and have them in mind during any laboratory setting you are in during your future chemistry laboratory classes. In addition, please study this Common Lab Equipment list. 1.
Wear safety goggles or safety glasses at all times. Regular eyeglasses are not appropriate safety glasses. 2.
Know the location of all safety equipment listed on the diagram of the lab. 3.
Never work alone in the laboratory or without permission of the instructor or lab supervisor. 4.
Do only the experiment assigned by the laboratory instructor. 5.
Wear clothing that is appropriate and closed-toed shoes. 6.
Place personal items such as purses, backpacks, etc., out of the way. 7.
Do not bring drinks or food into the lab. 8.
Dispose of waste materials according to the directions of the laboratory instructor. 9.
Clean lab station before leaving the lab. 10.
Use a ventilation hood when directed to do so. 11.
Use good judgment and care when working in the laboratory. 12.
Avoid touching hot objects. 13.
Read the labels on reagent bottles and containers to make certain that they contain the appropriate chemicals for the experiment and the appropriate concentration. 14.
Wash hands thoroughly before leaving the laboratory. 15.
Immediately report all physical and chemical injuries to the laboratory instructor, no matter how minor the injury seems. Part 2: Measurements________________________________________________________________ Scientific Notation: This lab provides practice for writing numbers in scientific notation (also called exponential notation) and significant figures (also called significant digits). In chemistry you frequently use very large numbers and also very small numbers. Scientific notation is used to express these very large or very small numbers. Because calculators sometimes give many nonzero digits in an answer, knowing how many digits to record in an answer is important. Recording Data
: You will be making measurements in virtual labs and simulations throughout the semester, and as you are recording and working with the data, you will be practicing skills in reporting data completely and correctly. These skills are not only important for tracking your work, but they also
Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu encode communication standards used by scientists around the world. The concepts of accuracy and precision are key foundational science communication standards. In the lab you will be using many tools to make measurements. Some of the tools will report measurements for you to copy down (e.g. an electronic balance), while others will require you to read a graduated scale. When we read the scale on a measuring tool, we report (1) the observed digits and (2) an estimated digit, and (3) the unit. The observed digits are reported from observing the divisions/scale on the measuring tool. The estimated digit is usually 1/10 of the smallest division of the scale of the measuring device. For Ruler 1 below, the smallest division is 0.1 cm. One-tenth of 0.1 cm is 0.01 cm. Thus measurements using Ruler 1 should be recorded to 0.01 cm (two decimal places). Verify these Ruler 1 measurements: Line 1 (green) measures 3.63 cm, and Line 2 (red) measures 6.52 cm. For Ruler 2, however, the smallest division is 1 cm. One-tenth of 1 cm is 0.1 cm, so measurments for Ruler 2 could be reported to one decimal place, 0.1 cm. Verify these Ruler 2 measurements: Line 1 (green) measures 3.6 cm, and Line 2 (red) measures 6.5 cm. Writing Conventions. In all of the sciences, numbers are written with their units, and standard practice is to embed decimal points between digits. For example, if a scientist is reporting the value for pressure “Pres” from the instrument display shown to the right, it is appropriate to report 0.10 psi
. The following are incorrect ways to report this data: .10 psi – this notation has a “dangling decimal” 0.10 – this notation is missing its units .10 – this notation is missing units and has a dangling decimal Definitions. In everyday language, the terms “accuracy” and “precision” are often used interchangeably. However, in science, these terms mean two very different things. Accuracy refers to how closely a measurement approaches the “true” measurement of a variable and incorporates aspects of “trueness” and “precision.”
1
Precision is a statement that describes the variation or scatter in data. Higher precision means there is less scatter in the data. For the two figures below assume that the 1
In the past decades, this definition for accuracy is shifting to the term “trueness.”
Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu center of the target represents the true meaning, and each black mark represents a measurement. Which figure shows data that is most accurate? Which is most precise?
2
Communicating About Accuracy and Precision of Tools. An important part of science communication is the reporting of precision of the tool used for any measurement. Scientists refer to the precision of a tool as its resolution. This is important because it allows the reader to understand the tool used, and what this tells about the precision in the data. The precision statement tells us what the most uncertain digit is in the measurement – this is the last digit that can be reported. The precision/resolution is stated using the plus-or-minus symbol, ±, the digit with the least certainty (the last digit), and the unit involved. For example, a collection of household thermometers might give these readings -- to the nearest two degrees: 54°F or 56°F or 58°F, with the uncertainty in the one’s place and allowing only even numbers for a resolution of ±2 °F; -- or to the nearest degree: 68°F or 69°F or 70°F, with the uncertainty in the one’s place, with a resolution of ±1 °F; -- or even to the nearest tenth-degree: 98.4°F or 98.5°F or 98.6°F with the uncertainty in the tenths place, for a resolution of ±0.1 °F. Another example: A balance is used to weigh samples of an ore. The readouts for three samples are 0.812g, 1.011g, 0.987g, 1.090g. From this data, we can see that the uncertainty of this measurement is in the last digit, or the thousands' place. Hence, for this balance, the resolution/precision is ±0.001 g. Precision/resolution is not calculated. It is observed from the instrument that is used for a measurement. Significant Figures: Significant figures are another science communication standard – a set of rules that scientists use as a shorthand way of maintaining the precision of a measurement throughout the use of that measurement. Significant figures refer to the number of digits that are measured and reported. The table below lists common laboratory instruments and number of decimal places to be recorded when using each. 2
Both figures show poor accuracy, although the one on the left is somewhat better. The figure on the right shows good precision.
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Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu Table 1: Units and Accuracy of Common Laboratory Equipment Unit Instrument Decimal Places mass triple beam balance, g 2 electronic balance, g 2 analytical balance, g 4 pressure barometer, mm Hg 1 length meter stick, cm 2 temperature lab thermometer, °C 1 volume 10 mL graduated cylinder, mL 2 100 mL graduated cylinder, mL 1 buret, mL 2 pipet, mL 2 Rules for Significant Figures The rules for identifying the number of significant figures in a number are listed below: 1)
Nonzero digits are always significant. 2)
Zeros are sometimes significant (they are not significant when holding decimal places). a)
Captive zeros – fall between nonzero digits and are always significant. i)
2007 – 4 sig figs ii)
10.05 – 4 sig figs b)
Leading zeros – precede all nonzero digits and are never significant. i)
0.0018 – 2 sig figs c)
Trailing zeros – at right end of the number. i)
After the decimal are always significant. (1) 0.3900 – 4 sig figs ii)
Before the decimal are significant only if (1)
the decimal point is written. (a)
200. – 3 sig figs (2)
bars are placed over significant zeros. (a)
2 00 – 3 sig figs (b)
2 0 0 – 2 sig figs (3)
the number written in scientific notation (best method) (a)
2 x 10
2
– 1 sig fig (b)
2.0 x 10
2
– 2 sig figs (a)
2.00 x 10
2
– 3 sig figs 3)
Exact numbers have infinite number of sig figs. Exact numbers include counting numbers or numbers used when defining a unit. i)
25 people in a room ii)
1m = 100 cm 4)
In scientific notation all digits in front of x 10 power
are significant. a)
1.45 x 10
-6
– 3 sig figs (0.00000145, leading zeros disappear in scientific notation)
Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu Rules for rounding off calculations: 1)
For multiplication and division, the answer has the same number of significant figures as the measurement with the fewest significant figures. 2)
For addition and subtraction, the answer has the same number of decimal places as the measurement with the fewest decimal places. 3)
Round only at the end of a series of calculations keeping track of significant figures or decimal places throughout the calculation.
Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu III.
Procedure Part 1: Safety_______________________________________________________________________ 1.
Read the following paragraph and list five things that the student did wrong in Part IV: Data Collection. Frank frequently missed lab. He decided to make up three labs on Friday afternoon. When he arrived at the lab, dressed in baggy shorts, a sweatshirt with floppy sleeves and flip flops, he could not find the lab supervisor. Since the lab door was open, he decided to start the first lab right away as he had to get to work early that day. No one was in the lab, but he saw the trays of chemicals on the center table. He remembered he had left his safety glasses at home, which was half an hour away from school. Since he was in a hurry, he started the lab without his glasses. He found the tray of chemicals that he needed, but was confused in the first part of one lab. The lab called for 1 M sodium hydroxide; he didn’t know what the 1 M stood for, but he did know the formula for sodium hydroxide. He noticed one bottle in a tray for another lab marked 6 M sodium hydroxide. Since the chemical had the correct name, he decided to use it. When he added the 6 M sodium hydroxide to the other chemical, it started reacting violently so he poured the mixture down the drain. After part one of the lab, he had to get to work so he left the chemical tray at the station and hurried out of the lab. 2.
Look at the Material Safety Data Sheet (MSDS) linked here: Copper (II) sulfate pentahydrate MSDS Sheet and answer the questions in Part IV: Data Collection. Part 2: Measurements________________________________________________________________ 1.
Perform the measurements stated and report the correct value using the correct number of decimal places and units. For online courses photographs are provided for the measurements that cannot be done at home.
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Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu IV.
Data Collection Part 1: Safety_______________________________________________________________________ 1.
List the mistakes below. Please answer in complete sentences. a.
Frank wore inappropriate attire to the lab.
b.
Frank didn’t wear safety goggles.
c.
Frank experimented alone in the lab.
d.
Frank incorrectly disposed of the mixture.
e.
Frank didn’t clean the lab before leaving
. 2.
Please answer in complete sentences.
a.
Is this flammable or non-flammable? (see Section 9)
It is non-flammable. b.
List one acute and one chronic health effect? (see Section 4) An acute effect this substance may cause is abdominal pain if swallowed. A chronic health effect this substance may cause is chronic copper poisoning c.
What kind of Personal Protective Equipment should be used when handling this substance? (see Section 8) Safety glasses should be used to handle this substance. d.
What is the appearance and color of this substance? (see Section 9) This substance is a blue solid color. Part 2: Measurements________________________________________________________________ 1.
Mass using a triple beam balance: a.
large test tube 22.65g
Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu b.
evaporating dish 60.64g c.
250mL beaker 109.2g d.
crucible tongs 70.74g 2.
Mass using an analytical balance:
Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu a.
large test tube 18.4282g b.
crucible & lid 30.9672g
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Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu c.
125 mL Erlenmeyer 89.2046g
d.
10 mL graduated cylinder 26.0174g
Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu e.
Room temperature using a thermometer: 21.9 f.
Length, width and depth of any textbook (or any book) in cm using a meter stick. Draw a sketch of your book labeling the dimension labeled l, w, and d. length: 10 width: 7 depth: 1.78
Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu 3.
Volume of liquid in graduated cylinders, dispensed by buret and pipet: a.
Volume of liquid in 10 mL grad. cylinder: 6.65ml b.
Volume of liquid in 100 ml grad. cylinder: 20.9ml
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Lab 1: Safety and Measurements Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu c.
Volume of liquid dispensed by burette: _35.9ml______ Initial Volume Reading Delivery Final Volume Reading 4.
How many significant figures are in each of the above measurements? a. b. c. d. e. f. 1. 4 6 3 2. 4 6 3 3 3. 4 6 3
Lab 1: Safety and Measurements General Chemistry I – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu V.
Applied Exercises For the following three cases (1-3), report the precision of the instruments, including both the uncertainty and the unit. 1.
The meteorologist reported the atmospheric pressure for each of these times: Clock Time 5:02:32 9:21:40 13:19:27 17:02:08 Pressure 764.8 mm Hg 763.2 mm Hg 762.9 mm Hg 763.4 mm Hg Clock time-low precision Pressure-high precision+ 1 mmhg 2.
The student recorded the mass of the same sample on the same balance (scale) three times: 84.91 grams, 84.90 grams, and 84.90 grams. High precision + 0.01 3.
The Mars Rover sent back the following air temperature data: -68.5
°
C, -32.7
°
C, -18.8
°
C. Low precision 4.
Express each of the following numbers in scientific notation with correct significant figures. a.
711.0 7.110x10^2 b.
0.239 2.39x10^-1 c.
90743 9.0743x10^4 d.
134.2 1.342x10^2 5.
How many significant figures are contained in each of the following measurements? a.
38.7 g 3 b.
2 x 10
18
m 1 c.
3,486,002 kg 7 d.
9.74150 x 10
-4
J 1 6.
The following quantities were reported on the labels of commercial products. Determine the number of significant figures in each. a.
0.0055 g salicylic acid 2 b.
12 tablets 2 c.
3% hydrogen peroxide 1 d.
5.5 fl. Ounces 2 7.
Classify the following sets of measurements as accurate, precise, both, or neither. a.
Checking the mass of chocolate chip cookies: 17.27 g, 13.05 g, 19.46 g, 16.92 g not precise
Lab 1: Safety and Measurements General Chemistry I – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu b.
Testing the volume of a batch of 25-mL pipettes: 27.02 mL, 26.99 mL, 26.97 mL, 27.01 mL precise c.
Determining the purity of gold: 99.9999%, 99.9998%, 99.9998%, 99.9999% precise
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Part B
Gather all of your pennies dated before 1982. Then follow the steps to complete the table. Include units as necessary.
Record the number of pennies dated before 1982.
Weigh (as a group) the pennies dated before 1982. Record the total mass. If you’re unfamiliar with using an electronic balance, watch this video before continuing.
Calculate and record the average mass of a single penny. If you need help with the calculation, visit the averaging data section of the math review.
number of pennies: 8
combined mass of the pennies (g): 49.2
average mass of a penny (g): 5.525
Part C
Now gather all of your pennies dated after 1982. Complete the table for the post-1982 pennies using the same steps from part B.
number of pennies: 9
combined mass of the pennies (g): 51.7
average mass of a penny (g): 5.744
Part D In parts B and C, you measured the average mass of each group of pennies. Now you’ll measure their volume. (For this part, assume that the pennies dated before and after…
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Part B
Gather all of your pennies dated before 1982. Then follow the steps to complete the table. Include units as necessary.
Record the number of pennies dated before 1982.
Weigh (as a group) the pennies dated before 1982. Record the total mass. If you’re unfamiliar with using an electronic balance, watch this video before continuing.
Calculate and record the average mass of a single penny. If you need help with the calculation, visit the averaging data section of the math review.
number of pennies: 8
combined mass of the pennies (g): 49.2
average mass of a penny (g): 5.525
Part C
Now gather all of your pennies dated after 1982. Complete the table for the post-1982 pennies using the same steps from part B.
number of pennies: 9
combined mass of the pennies (g): 51.7
average mass of a penny (g): 5.744
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Question 3: What is the molar mass of each of the following compounds?
A. C6H12O6
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1. Using the pictures below, record the displayed data in the data table in the report sheet. Make sure to include the right
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Mass measurement
7.1 g
Volume of water
measurement. There's
only one measurement
here – the larger image
is for magnification
only.
-20
15 m
Volume of water and
metal measurement.
There's only one
measurement here – the
larger image is for
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20 m
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DATA
Part B: Measuring the Mass of Materials
Top Loading Balance
Mass
Empty Beaker (g)
Mass of Beaker + Paper Clips (g)
Mass of Paper Clips (g)
Analytical Balance
Mass of Empty Beaker (g)
Mass of Beaker + Paper Clips (g)
Mass of Paper Clips (g)
DATA ANALYSIS:
1. Show your calculation for the mass of paper clips using the top-loading and analytical balances.
2. Which of the balances, top-loading or analytical, has the most uncertainty per measurement?
Explain.
Page 10 of 14
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Adding or subtracting and multiplying or dividing measurements
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gml1
Q
A
1
A chemistry student must write down in her lab notebook the concentration of a solution of sodium thiosulfate. The concentration of a solution equals the mass
of what's dissolved divided by the total volume of the solution.
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101 Chem101
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Question 19 of 44
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Using the information in the table, the rate law for the reaction A(g) + 3 B(g) →
C(g) + 2 D(g) is
Rate
[A], (M)
[B], (M)
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A.2 Area
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Length =
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- Part B Gather all of your pennies dated before 1982. Then follow the steps to complete the table. Include units as necessary. Record the number of pennies dated before 1982. Weigh (as a group) the pennies dated before 1982. Record the total mass. If you’re unfamiliar with using an electronic balance, watch this video before continuing. Calculate and record the average mass of a single penny. If you need help with the calculation, visit the averaging data section of the math review. number of pennies: 8 combined mass of the pennies (g): 49.2 average mass of a penny (g): 5.525 Part C Now gather all of your pennies dated after 1982. Complete the table for the post-1982 pennies using the same steps from part B. number of pennies: 9 combined mass of the pennies (g): 51.7 average mass of a penny (g): 5.744 Part D In parts B and C, you measured the average mass of each group of pennies. Now you’ll measure their volume. (For this part, assume that the pennies dated before and after…arrow_forwardPart B Gather all of your pennies dated before 1982. Then follow the steps to complete the table. Include units as necessary. Record the number of pennies dated before 1982. Weigh (as a group) the pennies dated before 1982. Record the total mass. If you’re unfamiliar with using an electronic balance, watch this video before continuing. Calculate and record the average mass of a single penny. If you need help with the calculation, visit the averaging data section of the math review. number of pennies: 8 combined mass of the pennies (g): 49.2 average mass of a penny (g): 5.525 Part C Now gather all of your pennies dated after 1982. Complete the table for the post-1982 pennies using the same steps from part B. number of pennies: 9 combined mass of the pennies (g): 51.7 average mass of a penny (g): 5.744 Part D In parts B and C, you measured the average mass of each group of pennies. Now you’ll measure their volume. (For this part, assume that the pennies dated before and after…arrow_forwardPlease answer question number 2 correctly with the correct answer. there is a picture of an example of a ''Dimensional analysis Format' below. please write out all work showing the math in dimensional analysis format. (please show all work) Question 3: What is the molar mass of each of the following compounds? A. C6H12O6 B. NaHCO3arrow_forward
- Part 3: Calculate density of a metal an unknown metal. 1. Using the pictures below, record the displayed data in the data table in the report sheet. Make sure to include the right number of significant figures in the measurements and calculations. Mass measurement 7.1 g Volume of water measurement. There's only one measurement here – the larger image is for magnification only. -20 15 m Volume of water and metal measurement. There's only one measurement here – the larger image is for magnification only. 20 m 15arrow_forwardHow do I solve for the percent value? The sample data calculated the answers but I have no idea how they obtained the percent error values. Calculate sample data #1 with detailed steps.arrow_forward4. When you get your 5th correct answer, you will get a certificate that you can share with your teacher letting your teacher know how you did. Please provide a screenshot of your certificate showing you got this completed. DATA Part B: Measuring the Mass of Materials Top Loading Balance Mass Empty Beaker (g) Mass of Beaker + Paper Clips (g) Mass of Paper Clips (g) Analytical Balance Mass of Empty Beaker (g) Mass of Beaker + Paper Clips (g) Mass of Paper Clips (g) DATA ANALYSIS: 1. Show your calculation for the mass of paper clips using the top-loading and analytical balances. 2. Which of the balances, top-loading or analytical, has the most uncertainty per measurement? Explain. Page 10 of 14arrow_forward
- In a gravimetric determination of lead content in brass, there is a constant loss by solubility of 1.55 mg of lead. A sample contains 7.86% by mass lead, and a 0.3514-g sample is used for the analytical determination using the gravimetric method. Calculate the % relative error. *Watch the units. **Provide your answer to two decimal places and without units. Avoid using scientific notation.arrow_forwardWhat are replicates in Analytical Chemistry? O The component of a sample that repeats over different assays. Similar assays done to different samples A sample that contains exactly the same amount of analytes than the original sample similar samples that are analyzed at the same time and in the same wayarrow_forwardPlease help with #5arrow_forward
- Please help with 7&8arrow_forwardPictures has my questionarrow_forwardMcGraw Hil ALEKS CHEMISTRY-Gener... esc E ! 1 MEASUREMENT AND MATTER Adding or subtracting and multiplying or dividing measurements Explanation -1 gml1 Q A 1 A chemistry student must write down in her lab notebook the concentration of a solution of sodium thiosulfate. The concentration of a solution equals the mass of what's dissolved divided by the total volume of the solution. Here's how the student prepared the solution: • The label on the graduated cylinder says: empty weight: 1.500 g • She put some solid sodium thiosulfate into the graduated cylinder and weighed it. With the sodium thiosulfate added, the cylinder weighed 96.6 g. She added water to the graduated cylinder and dissolved the sodium thiosulfate completely. Then she read the total volume of the solution from the markings on the graduated cylinder. The total volume of the solution was 97.7 mL. What concentration should the student write down in her lab notebook? Be sure your answer has the correct number of significant…arrow_forward
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