Question

The amount of manganese in steel is determined by changing it to permanganate ion. The steel is first dissolved in nitric acid, producing Mn2+ ions. These ions are then oxidized to the deeply colored MnO4- ions by periodate ion (IO4-) in acid solution. Calculate ℰ° and ΔG° at 25°C for each reaction

Answer 1

Answer:

The equations are:

3Mn + 2NO3- + 8H+ -----------> 3Mn2+ + 2NO + 2H2O

2Mn2+ + 5IO4- + 3H2O ---------> 2MnO4- + 5IO3-+ 6H

Ecell = 1.6 V - 1.51 V = 0.09 V

Using the equation of Nernst ,

 ΔG = -nFEcell

where n= number of electrons transferred = 10 mol

F = Farraday's constant = 96485 C/mol

Ecell = 0.09V

Now,   ΔG = -10 * 96485 C/mol * 0.09 V

ΔG = -86836.5 J/mol (\because C*V =J)

ΔG = -86.84 kJ/mol

Now, Ecell = (0.0591/n)*log K

0.09 = 0.0591/10 *logK

0.09 = 0.00591 * log K

log K = 0.09 / 0.00591

log K = 15.23

K = 10-15.23

  K = 5.89*10-16