The reaction between hydrochloric acid HCl and sodium thiosulphate Na2S2O3 can be represented by the following balanced chemical equation:2HCl + Na2S2O3 2NaCl + H2O + SO2 + SIn this reaction, hydrochloric acid donates a proton H+ to the sodium thiosulphate, which acts as a nucleophile. The rate of this reaction is influenced by the concentration of the reactants, temperature, and the pH of the solution.The pH of a solution is a measure of the concentration of hydrogen ions H+ in the solution. In the case of the reaction between HCl and Na2S2O3, the pH affects the reaction rate by influencing the concentration of H+ ions available for the reaction. As the pH decreases becoming more acidic , the concentration of H+ ions increases, which in turn increases the rate of the reaction.Conversely, as the pH increases becoming more basic , the concentration of H+ ions decreases, which slows down the reaction rate. However, it is important to note that the reaction between HCl and Na2S2O3 occurs in an acidic environment, as HCl is a strong acid. Therefore, the reaction rate would be significantly slower in a basic environment, as there would be fewer H+ ions available for the reaction.In summary, the pH affects the rate of the reaction between hydrochloric acid and sodium thiosulphate by influencing the concentration of H+ ions in the solution. Lower pH values more acidic result in a faster reaction rate, while higher pH values more basic result in a slower reaction rate.