The rate of a chemical reaction may depend on the concentration of one or more reactants or it may be independent of the concentration of a given reactant. The effect of concentration of the reactant on the rate of a chemical reaction can be studied by analysing the reaction between potassium iodate and sodium sulphite in presence of starch indicator at room temperature and pressure.. In acidic medium, potassium iodate is reduced to iodide ions by sodium sulphite. Iodide ions formed are oxidized to iodine by reaction with more iodate ions. The liberated iodine reacts immediately with sulphite ions forming iodide ions. When sulphite ions are completely consumed, the liberated iodine would react with starch solution, gives blue colour.
This video explains how to study the reaction rate of the reaction between potassium iodate and sodium sulphite using starch solution as indicator.