Applied Chemistry Problems

1) The lead batteries in cares are based on the following pair of half-reactions

PbO2 (s) + HSO4- (aq) + 3H+ (aq) + 2e- --> PbSo4 (s) + 2H2o (l); E=1.63V

PbSO4(s) + H+ (aq) + 2e- ---> Pb(s) + HSO4- (aq); E= -0.293V

a) Write the balanced cell reaction that occurs when a lead battery generates current.

b) Write the half-reaction that takes place at the anode

c) Write the half-reaction that takes place at the cathode.

d) Calculate E for a lead acid battery in which the sulfuric acid concentration (H2SO4) is 4.5 M (ie., [H+] = [HSO4-] = 4.5 M)

e) WHen a dead lead-acid battery is "jumped", or charged via attachment to a live battery, the danger exists of generating hydrogen which, if it escapes from the battery housing, could be ignited by an electrical spark. Why is the generation of hydrogen possible?

2) For each of the following unbalanced redox reactions:

(i) Balance the equation, referring to the tables of half-reactions as needed.
(ii) State the standard cell potential for each balanced reaction.

a) Cr(s) + NO3- (aq) --> Cr 3+ (aq) +NO (g), under acidic conditions

from the information given in part a...answer (i) and (ii)

b) Al (s) + MnO4 -(aq) --> Al 3+ (aq) + Mn 2+ (aq), under acidic conditions

answer (i) and (ii) for part b

c) Zn (s) + MnO2 (s) --> Zn 2+ (aq) + Mn2O3 (s) , under basic conditions

from the information given in part b...answer (i) and (ii)

4) One of the major eye irritants in smog is formaldehyde, CH2O, formed by the reaction of ozone, O3, with ethylene, C2H4: C2H4 (g) +O3(g) --> 2CH2O (g) + 1/2 O2 (g)

A) What are the relative rates of consumption of O3 and production of CH2O?

The initial rate (defined as -d[O3]/dt) was measured in a series of experiments, and the results are recorded below.

[O3]o (M), [C2H4]o (M), Initial Rate (M/min)
0.100, 0.200, 200.
0.100, 0.100, 50.0
0.300, 0.100, 150.

B) Using the data above, determine the rate law and the rate constant.

5) Consider the following mechanism for assembly of a DNA double helix from its strands, A and B:

A+B ---><--- unstable helis (fast, equilibrium)

the two arrows are double arrow..the top arrow going to the right is k1 and the arrow going to the left is k-1

Unstable helix --> stable double helix.

the arrow going to the right is k2

What is the rate law for the formation of the double helix? Express the overall rate constant in terms of the rate constants of the individual steps, i.e. k1, k-1, and k2

3) Use the table of reduction potentials in your text to help you answer the following questions. State your reasoning briefly, referring to data as appropriate.

a) Which is the stronger reducing agent, Na or K?

b) Will a copper penny dissolve in 1 M HCl?

c) Will a copper penny dissolve in 1 M HNO3?

d) Which is the stronger oxidizing agent , CLO4 - or MnO4 -?

e) Select a reagent that will oxidize Br- to Br2 but not Cl- to Cl2