Jack M. Barrack Hebrew Academy
2012 – 2013, Tri 3
Honors Chemistry
Dr. Darin Katz
Laboratory Experiment #8- Solution Chemistry
Thee objectives of this lab experiment are:
 to investigate the factors that increase the rate of solution formation;
 to investigate the relationship between solubility and heat of solution;
 to learn how to make serial dilutions of an aqueous solutions.
General Instructions:
1. Please read the attached lab sheets so that you are familiar with the procedure and
the type of data you will collect.
2. Please answer the attached pre-lab questions. They are due at the beginning of
your lab period. They will count toward your grade on this lab.
3. Important safety items and equipment: Wear your safety glasses, aprons, and
gloves during the entire experiment.
4. Some of the compounds you will be working with are corrosive or poisonous. Avoid
getting anything on your skin. If you do, immediately flush the area with water
and tell me!
Instructions for Lab Report:
Instructions for Lab Reports:
1. This WILL BE your formal lab report for Trimester 3. See Guidelines for Formal Lab
Reports.
2. Your lab report must contain the following:
a. Heading
b. Title
c. Introduction (only two paragraphs are required)
d. Materials and Methods
e. Data (this is where your data tables will go – remember to number and title properly!)
f. Conclusion and Analysis (including all required parts – see rubric)
3. Your lab reports are due on:
**You may compare data and calculations with your lab partner(s)
BUT the writing of your report and the answers to your post-lab
questions MUST be your own work.**
Laboratory Experiment #8- Solution Chemistry
Pre-lab Questions- Part I
Name
Complete these questions and turn them in at the beginning of your lab period.
1)
What are the three factors that hasten the formation of a solution? Explain why each
factors makes the solution form quicker.
2) In any solution, how can you always determine which is the solute and which is the
solvent?
3) You are instructed to prepare 200. mL of a 0.75 M aqueous sodium sulfate solution.
(a) What mass of sodium sulfate do you need? Show your work.
(b) Using information from the procedure of this lab, describe exactly how you would
prepare this solution.
Laboratory Experiment #8- Solution Chemistry
Pre-lab Questions- Part II
Name
Complete these questions and turn them in at the beginning of your lab period.
1) The solubility curve for potassium nitrate is shown above.
(a) What mass of KNO3 is needed to make a saturated solution at 60°C?
(b) At what temperature will dissolving 150 grams of KNO3 in 100 mL of water make
a saturated solution?
(c) If you completely dissolve 200 grams of KNO3 in 100 mL of water at 40°C, what
type of solution have you made?
Circle the correct answer- unsaturated
saturated
supersaturated
2) You are a chemist at “Beat Perk Industries”. You have a stock solution of 3.0 M
HNO3 (aq) and want to prepare 2.0 L of 1.0 M HNO3 (aq) using some of your
stock solution. Show calculations for how you will do this in the space below.
Part I- Materials and Procedure
Important Safety Items
1. Wear safety goggles, apron, and gloves.
2. Aqueous copper (II) sulfate may be an irritant to the skin. Avoid getting it on
your skin.
Materials
2- 100 mL Erlenmeyer flasks
Hot plate
Thermometer
100 mL volumetric flask
Parafilm
Mortar
Pestle
Electronic scale
Colored tape
Chemicals Needed
Sodium thiosulfate (s), Na2S2O3
Copper (II) sulfate pentahydrate, CuSO4 • 5 H2O
Procedure
Rate of Solution
1) Fill one 125 mL Erlenmeyer flask with about 100 mL of water. Place it on a hot
plate and heat the water to approximately 50°C.
2) Fill the other 125 mL Erlenmeyer flask with about 100 mL of room temperature
water. Add approximately 1.0 gram of sodium thiosulfate to the flask and record
the time it takes for the solid to dissolve. Do not stir or move the flask during this
time. Record the time in the data table for Part I. Move to step #3 while timing.
3) Using the mortar and pestle, crush 1.0 gram of sodium thiosulfate into powder.
Once the hot water reaches a temperature of approximately 50°C, add the
sodium thiosulfate powder to the hot water flask. Record the time it takes for the
solid to dissolve while swirling the flask in the data table for Part I.
Making an Aqueous Solution of copper (II) sulfate, CuSO4
1) Your group is assigned to make 100 mL. of a
CuSO4 • 5 H2O solution.
M aqueous
2) In the space provided, do calculations to determine the mass of CuSO4 • 5 H2O
needed.
3) Weigh the amount of CuSO4 • 5 H2O that you determined in Step #2 onto a
plastic weigh boat.
4) Add the CuSO4 • 5 H2O (s) to a 100 mL. volumetric flask. Fill the flask about
halfway with water and continuously swirl the flask to dissolve the solid.
5) Once the solid is completely dissolved, add water to the fill line. Add the water
very slowly so that you do NOT surpass the line.
6) Label the flask colored tape and your initials and seal the top with Parafilm.
Part II- Materials and Procedure
Important Safety Items
1. Wear safety goggles, apron, and gloves.
2. Aqueous copper (II) sulfate may be an irritant to the skin. Avoid getting it on
your skin.
Materials
test tubes
Bunsen burner
Stopper
Spectrophotometer tubes
sparker
tongs
spectrophotometer
Chemicals Needed
Sodium thiosulfate, NaS2O3
Aqueous copper (II) sulfate solution from Part I, CuSO4 (aq)
Procedure
Heat of Solution
1) Fill a test tube about halfway with water and add 2 heaping teaspoons of solid
Na2S2O3 to the test tube. Stopper the test tube and shake vigorously to try to
dissolve all of the solid.
2) If all of the solid dissolved, add another teaspoon of Na2S2O3, stopper, and shake
again. If all of the solid did not dissolve, skip to step #3.
3) Remove the stopper and using tongs, heat the test tube over a Bunsen burner
flame. Make sure to heat evenly and gently. Record your observations in the
data table for Part II.
Serial Dilutions of CuSO4 • 5 H2O (aq)
1) Using the CuSO4 • 5 H2O (aq) solution that you made in Part I, you will make two
dilutions from the list below. You can choose which two to make. The final
volume of each dilution will be 10 mL.
1:3 dilution (i.e., cut molarity by a factor of 3)
1:4 dilution (i.e., cut molarity by a factor of 4)
1:5 dilution (i.e., cut molarity by a factor of 5)
1:10 dilution (i.e., cut molarity by a factor of 10)
2) Do calculations below for both serial dilutions. Be sure to show work for exactly
how you will make each diluted solution from your original CuSO4 • 5 H2O
solution. Remember- the final volume of each solution will be 10 mL.
Dilution #1
Dilution #2
3) Following your work in #2 above, make both dilutions in separate test tubes. Be
sure to properly label each test tube with its new molarity.
4) Once you have made both dilutions, take your original CuSO4 (aq) solution from
Part I and your two serial dilutions to the spectrophotometer. DDK will help you
measure the amount of light (wavelength = 680 nm) absorbed by each of your
solutions. Record the absorbencies in your data table for Part II.
Data Table for Part I
Rate of Solution
NaS2O3 in
crystalline form
NaS2O3 in powder
form
Temperature of water
Stirring solution (yes or no)
Time for solid to dissolve
Making an Aqueous Solution of CuSO4
Show all calculations for the mass of CuSO4 (s) used to make your aqueous
solution.
Molarity of CuSO4 • 5 H2O (aq) = _______________________
Data Table for Part II
Heat of Solution
Describe your observations when a saturated solution of NaS2O3 was heated in the test
tube.
Serial Dilution of CuSO4
Solution
Original CuSO4
Dilution #1
Dilution #2
Calculations showing how
dilution was made
N/A
Molarity
Absorbance at 680 nm
Answer the following post-lab questions in your lab notebook. Type the question
first and then give the answer.
Post-Lab Questions
1) Describe what you observed about the effect of crushing the solute, stirring the
solution, and heating the solvent on the rate of solution. Provide explanations for
your observations.
2) Using your observations when heating the saturated solution of sodium
thiosulfate, does sodium thiosulfate have a positive or negative heat of solution?
Justify your answer with data from your experiment.
3) The heat of solution for lithium carbonate, Li2CO3 (s), is -27 kJ/mol. What would
you expect to observe if a saturated solution of lithium carbonate is heated over a
Bunsen burner flame?
4) Using your data table from Part II, create a graph of absorbance vs.
concentration for your three CuSO4 • 5 H2O (aq) solutions. Use a program like
Excel (or some other program on line) to create your graph; it cannot be a hand
graph. (Instructions on how to do this using Excel are below.)
Using internet resources, research Beer’s Law. What does Beer’s Law say
about the relationship between the concentration of a solution and its
absorbance? How well do your data obey Beer’s Law?
Generating an Absorbance vs. Concentration graph using Excel
1) Enter your data into Excel with Absorbance in one column and Concentration in another column.
2) Select all of the numerical data (not the column headers) and generate an ‘XY Scatter’ type of graph.
Top most example, no lines, only points
3) On the graph, select any one point; the points will become highlighted yellow
4) Right-click and select “Add Trendline”
5) In the ‘add trendline’ window, click the ‘options tab’
6) There are three check boxes at the bottom. Check the box that reads ‘display equation on chart’
7) Click ‘OK’
8) The equation of the best fit straight line will now appear in your graph, in the form of y=mx+b
9) Be sure to print your graph.