The rate constant k of the reaction between sodium thiosulfate Na2S2O3 and hydrochloric acid HCl at room temperature is not a fixed value, as it can vary depending on various factors such as concentration, temperature, and presence of catalysts. However, it can be determined experimentally using the following method:1. Prepare a series of solutions with different concentrations of sodium thiosulfate and hydrochloric acid. Make sure to keep the total volume of the solutions constant.2. Set up a stopwatch or timer to measure the time it takes for the reaction to complete.3. In a well-ventilated area, add the hydrochloric acid to the sodium thiosulfate solution and start the timer immediately.4. Observe the reaction, which produces a cloudy precipitate of sulfur S . The reaction is considered complete when the solution becomes opaque, and a marked black cross placed under the reaction vessel is no longer visible.5. Record the time it takes for the reaction to complete for each concentration of sodium thiosulfate and hydrochloric acid.6. Calculate the initial rate of the reaction for each trial by taking the inverse of the time it took for the reaction to complete 1/time .7. Plot the initial rate of the reaction against the concentration of sodium thiosulfate or hydrochloric acid. The slope of the resulting linear graph will give you the rate constant k for the reaction at room temperature.8. Analyze the data and calculate the rate constant k for the reaction between sodium thiosulfate and hydrochloric acid at room temperature.Keep in mind that the rate constant may vary between different trials and conditions, so it is essential to perform multiple trials and calculate an average value for the rate constant k .