Redox Reactions · Question 6

200 cc of x 10-3 M potassium dichromate is required to oxidise 750 cc of 0.6 M Mohr's salt solution in acidic medium. Here x = .

Answer

375

Solution

Mohr's salt supplies Fe2+, which is oxidised to Fe3+:

Cr2O72- + 6Fe2+ + 14H+ 2Cr3+ + 6Fe3+ + 7H2O

Moles of Fe2+ = 0.6 0.750 = 0.45 mol

Moles of Cr2O72- = 0.456 = 0.075 mol

Molarity of K2Cr2O7 = 0.0750.200 = 0.375 M = 375 10-3 M

x = 375

Answer: 375