3. Consider the following redox cell for the determination of vanadium by titrat

Question

3. Consider the following redox cell for the determination of vanadium by titration with Sn2+: Pt(s)VO2+(aq), V3+(aq) , H+ (1.0 M) Sn2+ (aq), Sn4+(aq) Pt(s)

a) Write the balanced titration reaction, showing all work!

b) Using Eo values from the supplemental tables, what would be the expected Ecathode at the equivalence point for this titration?

c) From the table below, select an appropriate redox indicator for this titration.

Indicator Eo (V)

Phenosafranine 0.28

Diphenylamine sulfonic acid 0.85

Tris(2,2’-bipyridine)ruthenium 1.29

Explanation / Answer

a) Sn+2 + 3VO+2 + 6H+= 3V3+ + Sn+4 +3H2O

B) At cathode :

VO+2 + 2H+ + e-= V3+ +H2O E0= +0.34V

VO+2 + 2H+ + e-= VO+2  +H2O   E0= +1.00V

V3+ + e- = V+2 E0= -0.26V

c) E0 of the overall reaction is 3*0.34-0.15= 0.87V

So we use Diphenylamine sulfonic acid as an indicator as its E0 = 0.85V close to 0.87V

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