Read the start, stir, read again. Compare the changes, fairly.
Temperature-change experiments come up in almost every IGCSE Chemistry Paper 6. Here 2.00 g of calcium chloride, then 2.00 g of ammonium chloride, dissolve in 25 cm³ of water in a polystyrene cup while the temperature is read every 30 seconds. Watch the set-up built step by step, then build it yourself and check it against the points the examiners look for.
Past-paper referenceOriginal experiment, wording and figures, written in the style of Cambridge IGCSE Chemistry 0620 Paper 6 (Alternative to Practical). It is not copied from a past paper. The “what the examiners said” notes are our paraphrase of the Principal Examiner Reports for Teachers.
Practise next: 0620/62 May/June 2025, (lithium chloride dissolving, highest temperature) · official past papers
Practise next: 0620/63 October/November 2024, (a solid dissolving, temperature against time) · official past papers
Practise next: 0620/62 February/March 2025, (zinc and iron with copper(II) sulfate) · official past papers
Examiner reports used: 0620 March 2025 (Paper 62), June 2023 (Paper 63), June 2024 (Paper 61), June 2025 (Paper 62), November 2023 (Paper 62), November 2024 (Paper 63) and November 2025 (Paper 63).
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What a full-mark diagram shows
The container
A polystyrene cup with a lid, standing in a beaker so it cannot tip. Polystyrene is an insulator, so less heat is lost or gained.
Measured quantities
25 cm³ of distilled water in a measuring cylinder read at eye level, and 2.00 g of solid weighed on a top-pan balance.
The readings
The initial temperature at 0 s, then every 30 s while stirring with the thermometer, each to the nearest 0.5 °C and written to 1 decimal place.
A fair comparison
Only the solid changes. Same mass, same volume of water, same cup and lid, same stirring and times; the cup rinsed and dried in between.
Habits the examiner reports keep asking for
Write every reading to the same resolution: 27.0, not 27, and read a thermometer to half a division.
Work out each change from the 0 s temperature, not from the reading before.
Exothermic means the temperature rose; endothermic means it fell. Compare temperature changes, not the highest temperatures.
Draw smooth curves of best fit and label each one. A best-fit line does not have to be straight.
Improve with a burette, a lid or insulation, and say why. A water bath or a digital thermometer is not an improvement.