Iodide ions, I⁻, and persulfate ions, S₂O₈²⁻, react according to the following equation. 2I⁻(aq) + S₂O₈²⁻(aq) → I₂(aq) + 2SO₄²⁻(aq) The rate of reaction between these ions can be determined from the time it takes for a certain amount of iodine, I₂(aq), to be produced. • A mixture of solutions is prepared, containing known volumes of ◦ aqueous ammonium persulfate, (NH₄)₂S₂O₈(aq), ◦ aqueous sodium thiosulfate, Na₂S₂O₃(aq), ◦ starch indicator. • A known volume of aqueous potassium iodide, KI(aq), is added to this mixture and a timer is started. • After the reactants are mixed, they react slowly to produce iodine, I₂(aq). • Any iodine initially produced is removed by a reaction with thiosulfate ions. I₂(aq) + 2S₂O₃²⁻(aq) → 2I⁻(aq) + S₄O₆²⁻(aq) • Iodine, I₂(aq), is continuously removed until all of the thiosulfate ions have been used up. • After that time any I₂(aq) that is produced turns the starch indicator blue. • The time of the first appearance of the blue colour is recorded. • This procedure is repeated with different volumes of reactants, keeping the total volume of the reaction mixture constant by adding the required volume of distilled water. You are to plan a series of experiments to determine the effect of changing the concentration of iodide ions on the rate of reaction. You are provided with the following materials. solid ammonium persulfate, (NH₄)₂S₂O₈(s) 0.20 mol dm⁻³ aqueous KI, a source of I⁻(aq) 0.0050 mol dm⁻³ aqueous Na₂S₂O₃, a source of S₂O₃²⁻(aq) starch indicator