The reaction between hydrochloric acid HCl and sodium thiosulfate Na2S2O3 can be represented by the following balanced chemical equation:2HCl + Na2S2O3 2NaCl + H2O + SO2 + SIn this reaction, HCl donates a proton H+ to the thiosulfate ion S2O3^2- , which leads to the formation of the products. The reaction rate depends on the concentration of both reactants, HCl and Na2S2O3, as well as the pH of the solution.The pH of a solution is a measure of the concentration of H+ ions, with lower pH values indicating higher concentrations of H+ ions more acidic and higher pH values indicating lower concentrations of H+ ions more basic . Since the reaction involves the transfer of a proton from HCl to the thiosulfate ion, the reaction rate is expected to be affected by the pH of the solution.In general, the reaction rate will increase with decreasing pH increasing acidity because there will be more H+ ions available to react with the thiosulfate ions. Conversely, the reaction rate will decrease with increasing pH decreasing acidity because there will be fewer H+ ions available to react with the thiosulfate ions.However, it is important to note that the relationship between pH and reaction rate may not be linear, and other factors such as temperature, ionic strength, and the presence of catalysts or inhibitors can also influence the reaction rate. Additionally, at extremely low or high pH values, the reaction rate may be affected by the stability of the reactants and products, as well as the potential for side reactions to occur.