Materials Required
Procedure
Real Lab Procedure
- Take four 250 ml conical flasks and label them as A, B, C and D.
- Add 5ml, 10 ml, 15 ml and 20 ml of 0.1 M potassium iodide (KI) solution to the flasks A, B, C and D respectively.
- Add 10ml of 2.5 M H2SO4 to each flask.
- To make the volume of the solution 100ml in each flask add water to them.
- Add 5 ml of starch solution to each flask.
- Add 10 ml of 0.05 M sodium thiosulphate (Na2S2O3) solution to each flask.
- Add 5 ml of 3% H2O2 solution to flask A and start the stop- watch immediately.
- Stir the mixture using a glass rod and wait for the blue colour to appear.
- Note the time when the blue colour just appears.
- Repeat the experiment by adding 5 ml of 3% hydrogen peroxide solution to flasks B, C and D and note the time required in each case for the blue colour first appears.
Simulator Procedure (as performed through the Online Labs)
- You can select the volume of potassium iodide (KI) solution using the slider.
- Drag the conical flask containing 0.1 M potassium iodide (KI) solution to the measuring jar to measure the solution.
- Drag the measuring jar to the conical flask to pour the solution in it.
- Drag the bottle to the measuring jar to measure 10ml 2.5 M sulphuric acid.
- Drag the measuring jar to the conical flask to pour sulphuric acid in it.
- Drag the beaker to the measuring jar to measure distilled water.
- Drag the measuring jar to the conical flask to pour water in it.
- Drag the bottle to the measuring jar to measure 5 ml starch solution.
- Drag the measuring jar to the conical flask to pour the starch solution in it.
- Drag the bottle to the measuring jar to measure 10 ml 0.05 M sodium thiosulphate (Na2S2O3) solution.
- Drag the measuring jar to the conical flask to pour sodium sulphite solution in it.
- Drag the bottle to the measuring jar to measure 5ml 3% hydrogen peroxide (H2O2) solution.
- Drag the measuring jar to the conical flask to pour hydrogen peroxide solution in it.
- You can get the time taken for the appearance of blue colour from the stopwatch.
- You can use the embedded worksheet to enter the values.
- You can plot a graph using the worksheet.
- To redo the experiment, click the ‘Reset’ button.
Note: Click on the ‘HELP’ button to see the instructions.
Observation
Record the observations as shown in the table given below:
Flask |
0.1 M KI solution (ml) |
2.5 M H2SO4 (ml) |
Water (ml) |
Starch solution (ml) |
0.05 M sodium thiosulphate solution (ml) |
3% H2O2 (ml) |
Time (t) for the appearance of blue colour (s) |
A |
5 |
10 |
85 |
5 |
10 |
5 |
|
B |
10 |
10 |
80 |
5 |
10 |
5 |
|
C |
15 |
10 |
75 |
5 |
10 |
5 |
|
D |
20 |
10 |
70 |
5 |
10 |
5 |
|
Conclusion
The rate of the reaction increases with an increase in the concentration of iodide ions.
Precaution
- Always use freshly prepared solution of sodium thiosulphate.
- Concentration of KI solution should be higher than the concentration of sodium thiosulphate solution.
- Use freshly prepared starch solution.