Rates of Reaction What affects the rate of reaction? 1) The surface area of the magnesium. 2) The temperature of the reaction. 3) Concentration of the hydrochloric acid. 4) Presence of a catalyst. In the experiment we use hydrochloric acid which reacts with the magnesium to form magnesium chloride. The hydrogen ions give hydrochloric acid its acidic properties, so that all solutions of hydrogen chloride and water have a sour taste; corrode active metals, forming metal chlorides and hydrogen; turn litmus red; neutralise alkalis; and react with salts of weak acids, forming chlorides and the weak acids. Magnesium, symbol Mg, silvery white meta