Iodine Clock
You are provided with the following solutions:
Aqueous sodium thiosulfate, Na2S2O3(aq)
Aqueous hydrogen peroxide, H2O2(aq)
Aqueous sulfuric acid H2SO4(aq), containing H+(aq) ions
Aqueous potassium iodide, KI(aq),containing I–(aq) ions
Irritant
Irritant
Irritant
Irritant
Distilled (or de-ionised) water
Starch solution
No hazard
No hazard
Step 1
Add the following into a conical flask.
1.
2.
3.
4.
5.
5.0 cm3 of sodium thiosulphate, Na2S2O3(aq);
25.0 cm3 of hydrogen peroxide, H2O2(aq);
5.0 cm3 of distilled (or de-ionised) water.
25.0 cm3 of H2SO4(aq)
10 drops of starch solution
Swirl the mixture thoroughly and place the flask on a white tile.
Step 2
1. Using a measuring cylinder, measure 10.0 cm3 of potassium iodide, KI(aq).
2. Pour the 10.0 cm3 of KI(aq) into the conical flask.
3. Immediately, start the stop clock
Swirl the mixture thoroughly and place the flask on the white tile.
Step 3
Observe the mixture until it changes colour (from colourless to blue).
Stop the clock when the blue colour first appears.
Record the time t, to the nearest second. This is Experiment 1.
Carry out Experiments 2, 3, in the same way as in Experiment 1 but using the different
volumes of H2O2(aq) and water given in the results table.