Question

The concentration of H3AsO3 in a solution is determined by titrating it with a 0.1807 M Ce4+ solution. The balanced net ionic equation for the reaction is: 2Ce4+(aq) + H3AsO3(aq) + 5H2O(l) 2Ce3+(aq) + H3AsO4(aq) + 2H3O+(aq) In one experiment, 22.27 mL of the 0.1807 M Ce4+ solution is required to react completely with 25.00 mL of the H3AsO3 solution. Calculate the concentration of the H3AsO3 solution?

Answer 1

Moles of Ce⁴⁺ are required for complete reaction = 22.27 mL x 0.1807 M = 4.024 mmol

Let us say that the concentration of H₃AsO₃ solution = Z M

Hence, the moles of H₃AsO₃ titrated = 25.00 mL x Z M = 25.00Z mmol

Now, from the equation given, it is clear that 1 mol of H₃AsO₃ is completely reacted by 2 mol of Ce⁴⁺

Therefore, 25.00Z mmol of H₃AsO₃ is completely reacted by = (2 mol x 25.00Z mmol)/1 mol = 50.00Z mmol of Ce⁴⁺

Now,

50.00Z mmol = 4.024 mmol

or, Z = 0.08048

Hence, the concentration of H₃AsO₃ solution = 0.08048 M