Changing the pH of a solution can affect the rate of reaction between hydrochloric acid HCl and sodium thiosulfate Na2S2O3 by altering the concentration of the reactants and the activity of the ions involved in the reaction. The reaction between HCl and Na2S2O3 can be represented by the following balanced equation:2HCl aq + Na2S2O3 aq 2NaCl aq + H2O l + SO2 g + S s In this reaction, the acidic HCl donates protons H+ to the sodium thiosulfate, which acts as a base. The rate of reaction depends on the concentration of both reactants, as well as the temperature and presence of any catalysts.When the pH of the solution is changed, the concentration of H+ ions in the solution is altered. If the pH is lowered more acidic , the concentration of H+ ions increases, which can lead to a faster reaction rate. Conversely, if the pH is raised more basic , the concentration of H+ ions decreases, which can result in a slower reaction rate.It is important to note that extreme changes in pH can potentially affect the stability of the reactants and products, as well as the overall reaction rate. For example, at very low pH values, the sodium thiosulfate may start to decompose, while at very high pH values, the hydrochloric acid may become less effective as an acid.In summary, changing the pH of a solution can affect the rate of reaction between hydrochloric acid and sodium thiosulfate by altering the concentration of H+ ions in the solution, which in turn influences the reaction rate. Generally, a more acidic solution will result in a faster reaction rate, while a more basic solution will result in a slower reaction rate. However, extreme changes in pH can also impact the stability of the reactants and products, potentially affecting the overall reaction rate.