| Aim | (a) To study the effect of concentration and temperature on the rate of reaction between Sodium Thiosulphate and Hydrochloric acid. (b) To study the reaction rates of the reaction between Potassium Iodate, (KIO3) and Sodium Sulphite: (Na2SO3) using starch solution as an indicator (clock reaction). |
| Apparatus Required | For experiment (a): Sodium thiosulphate solution Hydrochloric acid solution Water bath or hot plate Stopwatch or timer Dilute sodium hydroxide solution (to use as a stop solution) Measuring cylinder Conical flask Beaker Glass rod For experiment (b): Potassium iodate (KIO3) solution Sodium sulphite (Na2SO3) solution Starch solution Dilute hydrochloric acid Measuring cylinder Conical flask Beaker Stopwatch or timer Burette |
| Theory | (a) In this experiment, we will study the effect of concentration and temperature on the rate of reaction between Sodium Thiosulphate and Hydrochloric acid. The reaction is as follows: Na2S2O3 + 2HCl → 2NaCl + H2O + SO2 + S The reaction is a double displacement reaction where Sodium thiosulphate and Hydrochloric acid react to form Sodium chloride, water, Sulphur dioxide and a precipitate of Sulphur. The rate of the reaction can be affected by the concentration of the reactants and the temperature. The reaction rate is measured by observing the time taken for the precipitate to form. (b) In this experiment, we will study the reaction rates of the reaction between Potassium Iodate, (KIO3) and Sodium Sulphite: (Na2SO3) using starch solution as an indicator (clock reaction). The reaction is as follows: 2Na2SO3 + KIO3 + H2O → K2SO4 + 2Na2SO4 + 2I + 2H2O The reaction is a redox reaction where Potassium Iodate and Sodium Sulphite react to form Potassium sulphate, Sodium sulphate, iodine and water. The reaction rate can be determined by observing the time taken for the blue-black colour to appear due to the formation of iodine which then reacts with starch to form a blue-black complex. |
| Procedure | For experiment (a): Take a conical flask and add 10 mL of Sodium Thiosulphate solution and 5 mL of Hydrochloric acid solution. Stir the solution with a glass rod and start the stopwatch immediately. Observe the solution and note the time taken for the appearance of the yellow precipitate. Repeat the experiment by changing the concentration of the reactants and the temperature. Add a few drops of dilute sodium hydroxide solution to the flask to stop the reaction. Note down the observations and the time taken for the reaction to occur. For experiment (b): Take a conical flask and add 10 mL of Sodium Sulphite solution and 5 mL of Potassium Iodate solution. Add a few drops of dilute hydrochloric acid and swirl the flask to mix the solutions. Add 10 mL of starch solution and start the stopwatch immediately. Observe the solution and note the time taken for the blue-black colour to appear. Repeat the experiment by changing the concentration of the reactants. Note down the observations and the time taken for the blue-black colour to appear |
| Observation and Result | (a) Effect of concentration and temperature on the rate of reaction between Sodium Thiosulphate and Hydrochloric acid: As the concentration of the reactants increased, the rate of reaction increased. As the temperature increased, the rate of reaction increased. The rate of reaction was determined by measuring the time taken for the reaction mixture to turn opaque due to the formation of a yellow precipitate of sulphur. (b) Study of reaction rates of any one of the following: (i) Reaction of Iodide ion with Hydrogen Peroxide at room temperature using different concentrations of Iodide ions: The rate of reaction increased with increasing concentration of iodide ions. The reaction mixture turned blue due to the formation of iodine. (ii) Reaction between Potassium Iodate, (KIO3) and Sodium Sulphite: (Na2SO3) using starch solution as an indicator (clock reaction): The reaction mixture turned blue-black due to the formation of iodine. The time taken for the blue-black color to appear was measured. The rate of reaction was calculated by dividing the amount of product formed by the time taken for the reaction to occur. |