8.4: Procedure
- Page ID
- 549877
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Week 1:
You will be given the concentration and volume of the solutions you are to prepare. You will need to calculate the quantity of solute necessary to prepare the given volume of solution, then weigh out the appropriate amount of solute and dissolve to prepare the appropriate amount of solution. Prepare the solutions using the same technique as Lab 6. Show your calculations for determining the quantity of solute necessary to prepare the following solutions. (Remember to use correct units and significant figures.)
1. 100.0 mL of 0.200 M KI
mass of KI required to prepare 100.0 mL 0.200 M solution = __________
Prepare this solution and label. Use the top loading balance that weighs to the nearest 0.001 g.
2. 25.00 mL of 0.200 M KCl
mass of KCl required to prepare 25.00 mL of 0.200 M solution = __________
Prepare this solution and label. Use the top loading balance that weighs to the nearest 0.001 g.
The label for each solution should have the following information:
-concentration and chemical formula of substance
-name of substance
-date of preparation and your initials
Store these solutions in your lab desk drawer. You will use them in Part 2 of the experiment on chemical kinetics next week. Place the 25 mL volumetric flask inside a small beaker so that it cannot fall over.
Week 2:
1. In separate, labeled beakers, obtain approximately 100 mL each of KI and (NH4)2S2O8 and 60 mL of Na2S2O3. Reactions 1 - 5 will be carried out as described in Table 1. Use separate 100 mL or 10 mL graduated cylinders for measuring each solution. Label all glassware.
2. Carefully measure the appropriate amount of KI and (NH4)2S2O8 for reaction 1 into two separate 50 mL Erlenmeyer flasks. Label the flasks with the appropriate solution names. Be careful not to cross contaminate before starting the reaction
TABLE 1
|
Solutions |
0.200 M KI |
0.100 M (NH4)2S2O8 |
0.200 M KCl |
0.100 M (NH4)2SO4 |
0.0050 M Na2S2O3 |
|
Rxn 1 |
20.0 mL |
20.0 mL |
0 |
0 |
10.0 mL |
|
Rxn 2 |
10.0 mL |
20.0 mL |
10.0 mL |
0 |
10.0 mL |
|
Rxn 3 |
20.0 mL |
10.0 mL |
0.0 |
10.0 mL |
10.0 mL |
|
Rxn 4 |
Repeat Rxn 1 with the addition of one drop of 0.1 M CuSO4 to ammonium peroxydisulfate solution. |
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|
Rxn 5 |
Repeat Rxn 1 but warm the reactants to approximately 10 degrees above room temperature prior to mixing. |
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3. Dispense the Na2S2O3, KCl, and (NH4)2SO4 and 3-4 drops of starch solution into a 250 mL Erlenmeyer flask. This is your reaction flask. The KCl and (NH4)2SO4 do not react but are used to maintain a constant ionic strength for all solutions.
4. Simultaneously pour the KI and (NH4)2S2O8 solutions into the 250 mL flask, start the timer, and mix thoroughly by swirling the flask. Place the flask on a white piece of paper to see the color change better. Note the time the reactants are mixed and measure the time elapsed until the solution turns blue-black or amber. Record the time in Table 2. Measure the final temperature of the solution and record in Table 2.
5. Repeat steps 3-5 for each of the different sets of reaction conditions specified in Table 1.
The concentration of iodide ion and peroxydisulfate ion in each reacting solution can be determined from the volume of each solution used and the final total volume (50.0 mL in each case). For example, 20.0 mL of 0.200 M KI when diluted to a volume of 50.0 mL gives an iodide concentration of 0.0800 M I-. The concentrations of the reactants in each of the other reacting mixtures are determined in a similar manner and are tabulated in Table 2.
CALCULATIONS: Complete Table 2 as you complete calculations in A-L.
TABLE 2
|
Experiment |
time (s) |
Rate |
I- (M) |
S2O82 (M) |
k |
T (°C) |
|
1 |
0.0800 |
0.0400 |
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|
2 |
0.0400 |
0.0400 |
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|
3 |
0.0800 |
0.0200 |
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|
4 |
0.0800 |
0.0400 |
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|
5 |
0.0800 |
0.0400 |
A. Calculate the reaction rate for each of your reaction mixtures and record in Table 2. (Include units).
B. What two experiments do you need to compare to determine how the iodide concentration affects the reaction rate?
Experiments __________ and __________
C. Why did you choose the two experiments in part B?
D. Using the appropriate data, determine the value of m in the rate law. Round your value of m to the nearest whole number.
m = __________
E. What two experiments do you need to compare to determine how the peroxydisulfate concentration affects the reaction rate?
Experiments __________ and __________
F. Why did you choose the two experiments in part E?
G. Using your appropriate data, determine the value of n in the rate law. Round your value of n to the nearest whole number
n = __________
H. Rewrite equation (3) using the values of m and n you have determined.
I. Rearrange the rate law in step H to solve for the rate constant k. Do not use numbers, only variables.
J. Determine the values of k for experiments 1, 2, and 3 and record in Table 2. (Include units)
K. How did the addition of the catalyst, Cu2+, affect the rate of the reaction?
L. How did increasing the temperature affect the rate of the reaction?