Question

1) Based on your experimental rate law, is it possible that the decomposition of hydrogen peroxide over a platinum catalyst (2H2O2(aq) → 2H2O(l) + O2(g)) occurs in a single step? Briefly justify your response.

2) A student is preparing a sulfate buffer to maintain a pH of approximately 2.0. Given that the pKa of sodium bisulfate (NaHSO4) is 1.2, what ratio of sulfate (SO4 2- ) to bisulfate (HSO4 - ) would create a buffer of pH 2.0? The acid dissociation reaction of bisulfate into sulfate is shown below. Show work or provide a one or two sentence justification of your answer.

3) Consider having two acids, M and N, each with a concentration of approximately 0.10 M. Both acids are titrated separately with the same standard NaOH solution. The equivalence point pH of acid M is 8.9, while the equivalence point pH of acid N is 9.7. Which of the acids is considered the stronger acid? Circle your answer below and provide a one or two sentence justification of your answer.

4) A student took an absorbance measurement of a solution of green dye and reports the solution’s absorbance to be 0.739 a.u. At the end of lab, she noticed that the culture tube she used to take the absorbance measurement is covered in fingerprints. How will her measured absorbance compare to the true absorbance of the sample?

5) While these are not traditionally acidic compounds (pKa < 7), any compound can act as an acid in the presence of a sufficiently strong base. Compound A has a pKa of about 26, and compound B has a pKa of about 20. How will the stability of the conjugate base of C compare to the stabilities of the conjugate bases of A and B? Order the conjugate bases from most to least stable below

Answer 1

Solution:

The decomposition of H2O2 over a Pt catalyst occurs in two step.

Step 1: H2O2 + Pt    H2O + Pt(O)

Step 2: Pt(O) +   H2O2    H2O + O2 + Pt

Overall 2 H2O2   2H2O + O2

Step 1 is the rate determining step. The rate of the reaction is depending following factors;

1. Concentration of H2O2. Higher the concentration faster the reaction.
2. Surface area of the Pt catalyst. More the surface area faster the reaction.