When suspected drunk drivers are tested with a breath analyser, the alcohol (ethanol) in the exhaled breath is oxidised to ethanoic acid with an acidic solution of K 2 Cr 2 O 7 .
3CH 3 CH 2 OH + 2Cr 2 O 7 2– + 16H + ⎯→
3CH 3 COOH + 4Cr 3+ + 11H 2 O
The breath analyser measures the colour change and produces meter reading calibrated in terms of blood alcohol context
(i) Colour of testing solution changes from –
= 0.06 V and 
= 1.33 V. Therefore in the alcohol meter standard potential is – – 1.51 V (iii) What is the value of E for the reaction when the [CH 3 CH 2 OH] = [CH 3 COOH] = [Cr 2 O 7 2– ] = [Cr 3+ ] = 1(M) at pH = 4 : 0.955 V (iv) What is the concentration ratio of acetic to alcohol when the net e.m.f. is 1.33 V and other species are present at the concentration of 1 M ? 10 12
Text Solution
Verified by ExpertsA
(i)
Sol. K 2 Cr 2 O 7 ⎯→ Cr 3+ (orange) (green)
(ii)
Sol. 1.27 V
(iii)
Sol. E cell = E
0 cell – 
log
E cell = 1.27 + 
log [H + ] 16 E cell = 1.27 – 
× 0.059 × pH
= 1.27 – 
× 0.059 × 4 = 0.955 V
(iv)
Sol. 1.33 = 1.27 – 
log 
log 
or log 
= log 10
–4 or 
= 10
–4
Prepare Smarter with CGP Edu
Get practice questions, solutions, and test series in one place.
Write a Review
Share your experience with this question and solution.
Commentary
Send your comment, doubt, correction, or feedback to admin.
Similar Questions
Explore conceptually related problems