Question

A solution of permanganate is standardized by titration with oxalic acid (H2C2O4). It required 28.97 mL of the permanga- nate solution to react completely with 0.1058 g of oxalic acid. The unbalanced equation for the reaction is MnO4- (aq) + H2C2O4(aq) ----> Mn^2+ (aq) + CO2(g) What is the molarity of the permanganate solution?

Answer 1

balance

MnO4- (aq) + H2C2O4(aq) ----> Mn^2+ (aq) + CO2(g)

half reactions

MnO4- (aq) + ----> Mn^2+ (aq)

H2C2O4(aq) ----> + CO2(g)

balance charge/electrons and H+ H2O

MnO4− + 8 H+ + 5 e− ⇌ Mn2+ + 4 H2O

H2C2O4⇌ 2 CO2(g) + 2 H+ + 2 e−

balance e-

2MnO4− + 16H+ + 10 e− ⇌ 2Mn2+ + 8H2O

5H2C2O4⇌10CO2(g) + 10 H+ + 10 e−

invert acid and add all

5H2C2O4 + 2MnO4− + 16H+ + 10 e− ⇌ 2Mn2+ + 8H2O+10CO2(g) + 10 H+ + 10 e−

5H2C2O4 + 2MnO4− + 6H+ ⇌ 2Mn2+ + 8H2O+10CO2(g)

now..

mol of acid = mass/MW = 0.1058 /90.03 = 0.001175

mol of MnO4-:

ratio is 5:2 so

0.001175 mol of acid = 2/(5*0.001175) = 0.00047 mol of MnO4-

[KMnO4] = mol/V = 0.00047 / (28.97*10^-3) =0.016223 M