MYP 10

Unit 10.6.2: Measuring the average rate of a chemical reaction


  • To understand the difference between average rate and rate at a specific time
  • To produce data that will allow the calculation of average rate
  • To investigate the effect of concentration on rate of 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.

experiment sodium thiosulphate hydrochloric acid water
1 10ml 10ml 0
2 10ml 8ml 2ml
3 10ml 6ml 4ml
4 10ml 4ml 6ml
5 10ml 2ml 8ml

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

Experimental report.


Criterion C

Teaching notes

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.


The rates of chemical reactions

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