Potassium iodate(V) is a primary standard. It reacts with iodide ions in the presence of acid to form iodine. a standard solution of iodine can be prepared by weighing out the necessary quantity of potassium iodate(V) and making up to a known volume of solution. When a portion of this solution is added to an excess of potassium iodide in acid, a calculated amount of iodine is liberated.
1.015g of potassium iodate(V) are dissolved and made up to 250cm^3. To a 25.0cm^3 portion are added an excess of potassium iodide and dilute sulphuric acid. The solution is titrated with a solution of sodium thiosulphate, starch solution being added near the endpoint. 29.8cm^3 of thiosulphate are required. Calculate the concentration of the thiosulphate solution.
Note: 2S2O3(aq) + I2(aq) = 2I^-(aq) + S4O6^2-(aq)