Unit 10.6.2: Measuring the average rate of a chemical reaction
The students are guided through the experimental design to measure the average rate of reaction between sodium thiosulfate and hydrochloric acid.
Sodium thiosulfate (Mr = 248.18) 0.04 mol dm-3, prepared by dissolving 2.48g in water in a volumetric flask and making up to 250 ml.
Hydrochloric acid, 2 mol dm-3
The following mixtures are suggested.
The mixtures are shaken and the time taken for a cross drawn on the test-tube to become obscured when viewed from the other side.
Student follow up
The test-tubes need careful cleaning before the experiment to avoid contamination with acid.
After experimentation they need to be washed using a test-tube brush.