CEM 142 Recitation Problem Set 10 NAME ________________________
November 6th - November 12thMSU PID _________________
FALL SEMESTER 2012SCORE____/5
Balance the equation for the following reaction in basic aqueous solution:
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CrCl3(s) + H2O2(aq) → CrO42–(aq) + ClO4–(aq)
rc
re
di
t!
1. Breathalyzers use the following oxidation-reduction reaction to measure blood alcohol content:
3 CH3CH2OH(aq) + 2 Cr2O72–(aq) + 16 H+(aq) → 3 CH3CO2H(aq) + 4 Cr3+(aq) + 11 H2O(l)
in
2. rn
e
d
The color of the solution changes because some of the orange Cr2O72– is converted to the green Cr3+ as
ethanol CH3CH2OH is oxidized to acetic acid CH3CO2H. The Breathalyzer measures the color change
and produces a meter reading calibrated in terms of blood alcohol content.
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CH3CO2H(aq) + 4 H+(aq) + 4 e– → CH3CH2OH(aq) + H2O(l) E°red = 0.058 V
Cr2O72–(aq) + 14 H+(aq) + 6 e– → 2 Cr3+(aq) + 7 H2O(l)E°red = 1.33 V
What is E° for the reaction?
What is the value of E for the reaction, when the concentrations of ethanol, acetic acid, Cr2O72–, and
Cr3+ are 1.0 M and the pH is 4.0?
an
no
tb
e
C
3.
In an industrial electrolytic cell used for the purification of gold, a current of 25,000 amps was passed
through a cell containing a Au3+ salt for 24 hours. How much energy is used?
E°red Au3+(aq)|Au(s) = +1.50 V