Core Practical 13B Lab

Aims

To use a clock reaction to find the order of reaction with respect to iodide ions

To use a clock reaction to find the order of reaction with respect to peroxodisulfate ions

Equipment

● 100 cm3 of 0.2 mol dm–3 sodium peroxodisulfate solution ● 100 cm3 of 0.2 mol dm–3 potassium iodide solution ● 50 cm3 of 0.05 mol dm–3 sodium thiosulfate solution ● 20 cm3 of 1% starch solution ● distilled/deionised water ● white tile ● four 10 cm3 measuring cylinders ● dropping pipettes ● four 100 cm3 beakers ● four 250 cm3 beakers ● stop clock

1. Measure 10.0 cm3 of potassium iodide solution into a small beaker standing on a white tile.

2. Add 5.0 cm3 of sodium thiosulfate solution to the potassium iodide solution.

3. Add 10 drops of starch solution to the mixture in the small beaker. Starch acts as the indicator and must be used in each experiment.

4. Measure out 10.0 cm3 of the sodium peroxodisulfate solution. Pour this into the mixture prepared in steps 1 and 2. Start the stop clock.

5. Stop the clock when a blue colour appears in the beaker and note the time taken.

6. Make a copy of Table 2 from the ‘Analysis of results’ section. Use this to record your results.

7. Repeat steps 1–5 using the volumes of sodium peroxodisulfate and potassium iodide solutions shown in Table 1. The total volume including the sodium thiosulfate solution must add up to 25.0 cm3 , which can be achieved by adding the correct volume of distilled/deionised water.