Experiment 7.3:
Aim: To investigate the effect of temperature on the rate of reaction.
Problem statement: How does temperature affect the rate of reaction?
Hypothesis: The higher the temperature of the sodium thiosulphate solution, Na2S2O3, the shorter the time taken for the ‘X’ mark to disappear from view.
Variables:
(a) Manipulated : Temperature of sodium thiosulphate solution, Na2S2O3
(b) Responding : Time taken for the ‘X’ mark to disappear from view
(c) Fixed : Volume and concentration of sulphuric acid, H2SO4
Materials: 1.0 mol dm–3 sulphuric acid, H2SO4, 0.2 mol dm–3 sodium thiosulphate solution, Na2S2O3 and a piece of white paper with an ‘X’ mark in the middle
Apparatus: 150 cm3 conical flask, 10 cm3 and 50 cm3 measuring cylinders, stopwatch, thermometer, Bunsen burner, wire gauze and tripod stand
Procedure:
1. Put 50 cm3 of 0.2 mol dm–3 sodium thiosulphate solution, Na2S2O3 into a conical flask. Leave it for 5 minutes.
2. Record the temperature of the 0.2 mol dm–3 sodium thiosulphate solution, Na2S2O3.
3. Place the conical flask on the ‘X’ mark of the white paper.
4. Quickly, add in 5 cm3 of 1.0 mol dm–3 sulphuric acid, H2SO4 into the conical flask carefully. At the same time, start the stopwatch.
5. Swirl the conical flask gently and place it again on the ‘X’ mark.
6. Observe the ‘X’ mark vertically from the mouth of the conical flask.
7. Stop the stopwatch once the ‘X’ mark disappears from view.
8. Record the time taken when the ‘X’ mark disappears from view. that has been heated to 40 oC, 45 oC, 50 oC, and 55 oC.
9. Repeat steps 1 until 8 by using 50 cm3 of 0.2 mol dm–3 sodium thiosulphate solution, Na2S2O3
Interpreting data:
1. Use the data obtained to plot a graph of rate of reaction, 1/time against temperature of sodium thiosulphate solution, Na2S2O3.
2. Based on the graph, state the relationship between rate of reaction and the temperature of sodium thiosulphate solution, Na2S2O3.
Conclusion:
Is the hypothesis acceptable? What is the conclusion of the experiment?
Discussion:
1. Write the ionic equation for the reaction between sodium thiosulphate solution, Na2S2O3 and sulphuric acid, H2SO4.
2. Can sulphuric acid, H2SO4 be replaced with hydrochloric acid, HCl? Explain.
Answer:
Discussion:
1. S2O32–(aq) + 2H+(aq) → S(s) + SO2(g) + H2O(l)
2. Yes.
Thiosulphate ions, S2O32– react with hydrogen ions, H+ present in all acid solutions.
Aim: To investigate the effect of temperature on the rate of reaction.
Problem statement: How does temperature affect the rate of reaction?
Hypothesis: The higher the temperature of the sodium thiosulphate solution, Na2S2O3, the shorter the time taken for the ‘X’ mark to disappear from view.
Variables:
(a) Manipulated : Temperature of sodium thiosulphate solution, Na2S2O3
(b) Responding : Time taken for the ‘X’ mark to disappear from view
(c) Fixed : Volume and concentration of sulphuric acid, H2SO4
Materials: 1.0 mol dm–3 sulphuric acid, H2SO4, 0.2 mol dm–3 sodium thiosulphate solution, Na2S2O3 and a piece of white paper with an ‘X’ mark in the middle
Apparatus: 150 cm3 conical flask, 10 cm3 and 50 cm3 measuring cylinders, stopwatch, thermometer, Bunsen burner, wire gauze and tripod stand
Procedure:
1. Put 50 cm3 of 0.2 mol dm–3 sodium thiosulphate solution, Na2S2O3 into a conical flask. Leave it for 5 minutes.
2. Record the temperature of the 0.2 mol dm–3 sodium thiosulphate solution, Na2S2O3.
3. Place the conical flask on the ‘X’ mark of the white paper.
4. Quickly, add in 5 cm3 of 1.0 mol dm–3 sulphuric acid, H2SO4 into the conical flask carefully. At the same time, start the stopwatch.
5. Swirl the conical flask gently and place it again on the ‘X’ mark.
6. Observe the ‘X’ mark vertically from the mouth of the conical flask.
7. Stop the stopwatch once the ‘X’ mark disappears from view.
8. Record the time taken when the ‘X’ mark disappears from view. that has been heated to 40 oC, 45 oC, 50 oC, and 55 oC.
9. Repeat steps 1 until 8 by using 50 cm3 of 0.2 mol dm–3 sodium thiosulphate solution, Na2S2O3
Interpreting data:
1. Use the data obtained to plot a graph of rate of reaction, 1/time against temperature of sodium thiosulphate solution, Na2S2O3.
2. Based on the graph, state the relationship between rate of reaction and the temperature of sodium thiosulphate solution, Na2S2O3.
Conclusion:
Is the hypothesis acceptable? What is the conclusion of the experiment?
Discussion:
1. Write the ionic equation for the reaction between sodium thiosulphate solution, Na2S2O3 and sulphuric acid, H2SO4.
2. Can sulphuric acid, H2SO4 be replaced with hydrochloric acid, HCl? Explain.
Answer:
Discussion:
1. S2O32–(aq) + 2H+(aq) → S(s) + SO2(g) + H2O(l)
2. Yes.
Thiosulphate ions, S2O32– react with hydrogen ions, H+ present in all acid solutions.