# For run #1 compare the instantaneous reaction rates at 12 seconds and 160 seconds and use the concentratons of crystal violet at these times and kinetic theory to explain the difference in observed rates.

Pt1

- For run #1 compare the instantaneous reaction rates at 12 seconds and 160 seconds and use the concentratons of crystal violet at these times and kinetic theory to explain the difference in observed rates. Do the same for run # 2.
- Compare the rates at 12 seconds for runs #1 and #2 with each other. Since these were run at different concentrations of [OH-], and started with the same [CV} use this difference to explain the different rates and crystal violet concentrations observed.

Pt2

* For acid solution calculation, assume you have only acid in water at same concentration of acid in buffered solution

** Do not attempt to measure as the probe cannot accurately measure pH of deionized water.

1. Use ionization, common ion and equilibrium considerations to explain why the pH of, pure acid, buffer A and buffer B have their relative values.

2. For each solution, how well do the measured and calculated pH values compare?

1. Discuss the reason for the difference in the volume of HCl needed to bring water and solution A to pH 2.5.

2. Compare the volume of HCl needed to bring solutions A and B to pH 2.5. a. What is the ratio of HCl volume used for A to B? __________

b. What is he HCl reacting with in the solutions? __________

c. Write the equation for the reaction of the H3O+ ion (from the HCl) with the buffered solution.

d. What is the ratio of the concentration of NaC2H3O2 in A to B? ____________

e. Compare the concentration ratio from (d) to the volume of HCl ratio reported in (a) and explain the reason for the difference in HCl volume for A and B in terms of the buffering reaction. The expected ratio is 2/1. If your results are significantly different, base your explanation on the 2/1 ratio

e. Compare the ratios of acetic acid moles in A and B to NaOH volumes A and B and explain the results. The expected ratio is 1/1. If your results are significantly different, base your explanation on the 1/1 values.

3. Examine the volume results for A and B when HCl is added and the volume results for A and B when NaOH is added.

In terms of the reactions, explain why NaOH volumes for A and B are approximately 1/1 and the HCl volume ratio is approximately are 2/1?

Pt3

a. Record the experimental cell potentials below.

- Use the results from the measurements of runs 1-6 to write the correct half-cell reactions and the overall reaction for each of the six cells listed in table 1. Write the equations in the space provided below. Clearly identify which half-cell is the oxidation reaction and which the reduction and identify the anode and cathode. This can be further confirmed by examining tests 4-6 and noting what color connection each has when giving a positive voltage reading.
- Calculate the standard cell potential for each cell from standard reduction potential table values and compare to the measured value. Since all concentrations are the same, the ratios for Qc in the Nernst equation will be 1 so the standard potentials can be used. Record the calculated results below.
- d. How well do the measured cell potential values compare to the calculated values for each cell?
- e. From your experimental data cell potentials, runs 1-3, not the standard reduction potential table, list the oxidation potential order for the metals Cu, Fe, Pb and Zn.
- Analysis Guidance: In tests 1-3 the copper electrode has the same red connection while the black is changed to Zn, Fe and Pb and the voltage read is positive in each test. If you assume copper is the cathode, reduction electrode, then the other metals are the anode, oxidation electrode. This can then be used to write the correct half-cell reactions versus copper.For run #1 compare the instantaneous reaction rates at 12 seconds and 160 seconds and use the concentratons of crystal violet at these times and kinetic theory to explain the difference in observed rates.

By comparing the potential value for the Zn, Fe and Pb combined with copper, the relative potential for oxidation of the metals can be determined and the order they would appear in the standard reduction table determined.

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- f. Explain how you arrived at the order reported in item 3 from you experimental data... (See analysis guide earlier
- g. How well does your order compare to the actual order as determined from the calculated Eo cell potentials?
- In this experiment you are determining the effects of anode and cathode solution concentrations of the cell potential.
- 1. Comparison of potential measurements tests 1 and 3

b. How does the cell potential change from test 1 to test 3?

c. Use the concentration changes and equilibrium concepts of reactions to explain the reason for the voltage change and why it is in the direction found. (Using concentration ratio, i.e. the Nerntz equation or saying the reaction goes forward or reverse are not acceptable answers.)

Show Nerntz equation calculations and results for tests 1 and 3. For all E values in the calculations use the value you obtained from test 1.

e. Compare whether the increase or decrease in cell voltage seen in the test measurements agrees qualitatively with the direction of change predicted by the Nernst equation.

b. How does the cell potential change from test 1 to test 2?

c. Use the concentration changes and equilibrium concepts of reactions to explain the reason for the voltage change and why it is in the direction found. (Using concentration ratio, i.e. the Nerntz equation or saying the reaction goes forward or reverse are not acceptable answers.)

d. Show Nerntz equation calculation and results for test 2. For E, use the value you obtained from test 1.

e. Compare whether the increase or decrease in cell voltage seen in the test measurements agrees qualitative with the direction of change predicted by the Nernst equation. Use the potential calculated for test 1 earlier for the comparison.

3. Examine the graph of log [Cu+2] versus cell potential obtained in experiment 2.

- Use the theoretical plot to develop a conclusion on how the cell potential changes with changes of the copper solution concentration.

m. Does the graph of your experimental data agree with the general conclusion above?

- Completely consistent experimental results would have your experimental line identical with the theoretical line. (1) How well do the two lines compare in slope? Slope: experimental ____________ theoretical _________ (2) Circle the experimental points, (triangles) on the graph. Discuss the scatter of your experimental data points and how this compares to the correlation coefficient for the line. A perfect correlation to a straight line is 1.0 (3) Use the observations in (1) and (2) to comment on the overall quality of your experimental results.

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