Question

The concentration of SO32- in a solution is determined by titrating it with a 0.1780 M dichromate solution. The balanced net ionic equation for the reaction is:
Cr2O72-(aq) + 3SO32-(aq) + 8H3O+(aq) 2Cr3+(aq) + 3SO42-(aq) + 12H2O(l)

In one experiment, 24.94 mL of the 0.1780 M dichromate solution is required to react completely with 40.00 mL of the SO32- solution. Calculate the concentration of the SO32- solution.

________ M

Answer 1

n(Cr₂O₇^2-) = C x V = 0.02494 L x 0.178 M = 0.00444 mol.

According to the equation n(SO₃^2-) = 3 x 0.00444 = 0.01332 mol.

C(SO₃^2-) = n/V = 0.01332mol / 0.04 L = 0.333 M.

0.333 M