Calculate the moles of ascorbic acid and the molarity of the unknown solution based on the following information.

Question

You have 5 mL of an unknown solution, and 50 mL of distilled water and 1 mL of starch indicator solution is added. The sample is titrated and uses a total of 20.5 mL of iodine. The iodine solution is 0.005 mol/L and the starch indicator solution is 0.5%.

Calculate the moles of ascorbic acid and the molarity of the unknown solution based on the following information.

Answer 1

You have 5 mL of an unknown solution, and 50 mL of distilled water and 1 mL of starch indicator solution is added. The sample is titrated and uses a total of 20.5 mL of iodine. The iodine solution is 0.005 mol/L and the starch indicator solution is 0.5%.

Calculate the moles of ascorbic acid and the molarity of the unknown solution based on the following information.

Assuming that the "unknown solution" is just ascorbic acid of unknown concentration, we start by obtaining the moles of iodine consumed in the titration.

0.005 mol/L * 20.5 mL / 1000 ml/L = 0.0001025 mol I₂

The net redox reaction between the iodine (I₂) and ascorbic acid (AA) is

C₆H₈O₆ + I₂ → C₆H₆O₆ + 2 I^- + 2 H⁺

This shows that the stoichiometric ratio in the balanced equation is 1:1 for the reactants. Therefore,

0.0001025 mol I₂ consumes 0.0001025 mol AA.

Since this amount of ascorbic acid was dissolved in the original 5 ml of unknown solution, the original concentration of AA is

0.0001025 moles * 1000 ml/L / 5 mL = 0.0205 mol/L = 0.0205 M