5 Steps to a 5 AP Chemistry 2019

330 ❯ STEP 5. Build Your Test-Taking Confidence

Question 2

Selenous acid, H 2 SeO 3 , reacts with hydrogen peroxide, H 2 O 2 , in acid solution according to the following

equation:

H 2 SeO 3 (aq) + H 2 O 2 (aq) → HSeO 4 – (aq) + H+(aq) + H 2 O(l)

The following information was obtained in a series of reactions:

EXPERIMENT

INITIAL CONCENTRATIONS (MOLARITIES) RATE OF

DISAPPEARANCE

[H 2 SeO 3 ] [H 2 O 2 ] [H+] OF H 2 SeO 3 (M S–1)

1 0.100 0.100 0.100 7.4 × 10 –8

2 0.200 0.100 0.100 2.9 × 10 –7

3 0.100 0.200 0.100 1.5 × 10 –7

4 0.100 0.100 0.200 3.7 × 10 –8

(a) Determine the order of the reaction for H 2 SeO 3 , H 2 O 2 , and H+. Justify your answers.

(b) Write the rate law for the reaction.

(c) Determine the value of the rate constant including units.

(d) (i) Is H 2 O 2 acting as an oxidizing or as a reducing agent?

(ii) What is the oxidation state of oxygen in H 2 O 2?

(iii) Write the balanced half-reaction for H 2 O 2 in this reaction.

A

B

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