The reaction between hydrochloric acid HCl and sodium thiosulphate Na2S2O3 can be represented by the following equation:HCl + Na2S2O3 2NaCl + H2O + SO2 + SThe effect of pH on the rate of this reaction can be understood in terms of the reaction mechanism and the role of H+ ions protons in the reaction. The reaction mechanism involves a nucleophilic attack of the thiosulphate ion S2O3^2- on the proton H+ from the hydrochloric acid. This leads to the formation of an intermediate species, which then decomposes to form the products.In general, the rate of this reaction increases with increasing acidity lower pH . This is because a higher concentration of H+ ions in the solution increases the likelihood of the nucleophilic attack occurring, thus increasing the reaction rate. Conversely, as the pH of the solution increases becomes less acidic , the concentration of H+ ions decreases, leading to a slower reaction rate.However, it is important to note that the reaction between HCl and Na2S2O3 is relatively fast even at moderately acidic pH levels. Therefore, while the reaction rate does depend on the pH, the effect may not be as pronounced as in some other reactions that are more sensitive to changes in pH.In summary, the rate of the reaction between hydrochloric acid and sodium thiosulphate generally increases with increasing acidity lower pH due to the increased concentration of H+ ions, which promotes the nucleophilic attack in the reaction mechanism.