lab report 2

You obtain an Unknown Sample from the Stockroom.  You begin testing the solution through the steps outlined in the flowchart of the experiment’s PDF file.  You first add HCl and centrifuge your mixture.  You observe the formation of a white precipitate in the bottom of the test tube.   After pouring off the supernatant liquid, you add hot water to the white precipitate.  Addition of the hot water dissolves some of the precipitate, but some white precipitate still remains on the bottom of the test tube.  You pour off the supernatant liquid, and add ammonia (NH3) to the remaining precipitate.  You now observe the formation of a gray-black precipitate. Which of the following is a valid conclusion to draw at this point? Select one:     Hg22+ is definitely present.   Pb2+ is definitely present.   Ag+ could be present, or Hg22+ could be present, or BOTH could be present.   Ag+ is definitely present

Dangerous Paint Stripper Jessica has a summer job working for the city parks program. She has been using a cleaner called “Graffiti Gone” to remove graffiti from the bathrooms. She has to take a lot of breaks, because the chemical makes her throat burn. It also makes her feel dizzy sometimes, especially when the bathrooms don’t have very many windows. On the label, she sees that the cleaner has methylene chloride in it. She feels like she’s managing to get the work done, but she is worried about feeling dizzy. She wants to find out more about this chemical, what harm it can cause, and whether there are safer ways to do this work. Questions for following story. 1. What went right in this situation? 2. What went wrong in this situation? 3. What steps should be taken in this workplace to make sure employees are better protected and prepared the next time?

PART 3- LABORATORY EQUIPMENT EQUIPMENT NAME FUNCTION To hold test tubes. Attaches to a retort stand to support glassware being heated. To pour liquid from a large container into a small container. To provide a flame during an experiment. ones To light the Bunsen burner. To attach test tubes to a retort stand. To clean substances out of a test tube. To hold a hot crucible or flask. To hold a hot test tube. To place on the lab bench to prevent burning or to use with ring clamp. To transfer small amounts of liquid. To grow bacteria or contain small experiments. To hold liquids. To measure liquids. To contain experiments (a stopper can be used to close the flask). To hold a hot beaker. To perform an experiment with a different substance in each well. To hold chemicals and perform experiments in. To scoop and transfer small amounts of substances, To stir during experiments that involve mixing or dissolving.

Which one answer does NOT represent a characteristic of a good recrystallizing solvent? O 1) Should not react with sample. O 2) Should do a poor job of dissolving impurities when hot. O 3) Should have a moderate boiling point. O 4) Should do a good job dissolving a sample when cold.

Can I get detailed explanation for this table , mentioning the apparatus and when’s the timer is started ? What happens next

You obtain an Unknown Sample from the Stockroom.  You begin testing the solution through the steps outlined in the flowchart of the experiment’s PDF file.  You first add HCl and centrifuge your mixture.  You observe the formation of a white precipitate in the bottom of the test tube.   After pouring off the supernatant liquid, you add hot water to the white precipitate.  Upon addition of the hot water, you have some white precipitate still at the bottom of the test tube, and the supernatant liquid is poured off.  To this liquid, potassium chromate (K2CrO4) is added.  Upon this addition of potassium chromate, you observe no formation of precipitate. Which of the following is a valid conclusion to draw at this point? (Choose one.)   Select one:   1. Hg22+ is definitely present.   2. Pb2+ is NOT present. 3. Ag+ is definitely present. 4. Pb2+ is definitely present.

10 mL of 10 % sodium sulphate solution into a clean test tube. Add 1 drop of 10 % barium chloride. What do you observe? Write an equation to explain your observations in your lab report. C2. Measure out a fresh 10 mL portion of 10 % sodium sulphate into another test tube. Making sure to count the drops, use a dropper to add 30 % calcium chloride solution. Swirl the solution after each drop. Continue until a white precipitate occurs. Write an equation to explain your observations. Which solubility product has the smaller numerical value, that for calcium sulphate or barium sulphate? Explain how you know this is true. C3. Measure out another 10 mL portion of 10 % sodium sulphate into a clean test tube. Add 8 drops of 50 % sulphuric acid and swirl. Count the number of drops (swirl after each drop) of 30 % calcium chloride needed to produce a precipitate of calcium sulphate. Explain why the number of drops of calcium chloride differs in the two experiments. I need equations, observations…

Balance

Table 5, Dissolved oxygen of distilled water at different temperatures Temperature (C) Volume of aliquot (ml.) 5.00 Volume of sodium thiosulfate used (mL) Dissolved oxygen (ppm) 10.3 4 13.60 25 5.00 12.20 8.23 73 5.00 5.40 4.03 1. From your data, calculate the dissolved oxygen content in distilled water at 73 °C (data in Table 5) without using the DO formula. Detailed calculation and formulas are required in this answer.

A student wants to determine how different factors affect the rate of dissolving a solid in water. The student will test: the size of the particles, the temperature of the water and the amount of agitation or stirring. Investigation Particle size Temperature (°C) Stirring small 59 yes small 38 yes 3 small 60 yes Which investigation will have the slowest rate of dissolving and why? Use evidence to explain your answer.

Using recrystallization techniques, a student attempts to purify 0.50 g of compound H. Based on the solubility of H in the chosen solvent at collection temperature, the maximum percent recovery is 82%. The student obtains 0.396 g of purified crystals. What is their percent recovery? Group of answer choices 41% 64% 79% 82% 97% none of these

Write balanced equations for the reaction of Al(OH)g with stomach acid (HCI). Express your answer as a chemical equation. Identify all of the phases in your answer. | ΑΣφ ? Submit Request Answer Part B Write balanced equations for the reaction of Mg(OH), with stomach acid (HCI). Express your answer as a chemical equation. Identify all of the phases in your answer.

2. Show solution. Thanks!

The spectroscopic data in the table is generated with five solutions of known concentration. Concentration (M) 0.0133 m= 0.0266 0.0532 0.106 0.213 Absorbance 0.1271 What is the intercept of the linear regression line? 0.08531 0.5388 1.069 Use a spreadsheet program, such as Microsoft Excel, to graph the data points and determine the equation of the best-fit line. 1.954 What is the slope of the linear regression line formed by these points? M-1

Explain why one would recrystallize a solid from a solvent pair instead of a single solvent.  Explain how it works in terms of solubilities.    please give detail, will only rate if sufficent detail is given. thank you!

You are attempting to purify a compound via recrystallization. You prepare the process through the following method: 1) Dissolve the material in a minimal amount of hot EtOH. 2) Slowly add hot water until the compound is slightly cloudy. 3) Add a small amount of EtOH until the solution is just clear (still hot). 4) Cool to RT. Upon cooling to RT you notice that the compound is not precipitating out of solution. You decide to boil off some ethanol. Upon completing this step and cooling to RT you notice that the compound is precipitating out as desired! In which solvent is your compound the least soluble? Ethanol O Water O The ethanol water mixture Insoluble in all of these solvents

can you please answer the question on the picture, make sure to show all of your work and POST PICTURES OF ALL OF YOUR WORK. Thank you.

A student performs a crystallization on an impure sample of biphenyl. The sample weighs 0.5 g and contains about 5% impurity. Based on his knowledge of solubility, the student decides to use benzene as the solvent. After crystallization, the crystals are dried and the nal weight is found to be 0.02 g. Assume that all steps in the crystallization are performed correctly, there are no spills, and the student lost very little solid on any glassware or in any of the transfers. Why is the recovery so low?

Table 2: Absorbance Values of Standards and Unknowns. Sample Blank Standard Solution 1 Standard Solution 2 Standard Solution 3 Standard Solution 4 Standard Solution 5 Water Sample 1 Water Sample 2 Phosphate Concentration (in ppm) Y17 0 ppm 0.02 ppm 0.04 ppm 0.08 ppm 0.16 ppm 0.32 ppm Freeman Lake 0.001 0.325 0.292 0.413 0.315 0.039 0.054 0.049 Absorbance at 2= 690 nm Calculations: 1. Construct a phosphate standard curve in Excel by plotting concentration (in ppm) on your x-axis and Absorbance (unitless) on your y-axis for your known solutions. Label the axes on the graph and provide the curve with a title. Use a linear trendline to generate a best fit line to your data. Label the graph with the equation and the R" value. Insert your labeled graph in the space below. X

From the data in Table 2.5, compute the concentration of the undiluted and diluted ovalbumin samples (make sure to account for the appropriate dilution factors, DF, in the computation).

6. Suppose you have a mixture of water and your 2-bromo-2-methylbutane product in a separatory funnel. Use densities to predict which phase will be the top layer in the funnel. a. 2-bromo-2-methylbutane (organic phase) b. water (aqueous phase) c. there would only be one phase since the substances are miscible