Paper 5 / Paper 6 workout · Question 1 style · 19 marks
Two blue solutions, one thermometer. Which is stronger?
Zinc powder displaces copper from copper(II) sulfate solution and the mixture warms up. By hand, measure 20 cm³ of solution J into a polystyrene cup, read the starting temperature, tip in the zinc, stir with the thermometer and read it every 30 seconds. Then do the same with solution K, plot both sets of temperature changes as two labelled curves and decide which solution is more concentrated. Every attempt uses different concentrations. Allow about 35 minutes.
Past-paper referenceOriginal experiment, wording and numbers, written in the style of Cambridge IGCSE Chemistry 0620 Paper 5 (Practical Test) and Paper 6 (Alternative to Practical). It is not copied from a past paper.This type of experiment has come up 21 times (10 in Paper 5, the Practical Test, and 11 in Paper 6, the Alternative to Practical) in the past papers we checked. Show the list
Checked: Cambridge IGCSE Chemistry 0620 Papers 5 and 6, 2020 to 2025. Only the papers in our collection are listed, so the real number may be higher. Question papers are available from Cambridge.
This workout needs JavaScript.
How this question is marked
Results (a), (b)
For each experiment: every temperature and temperature change to the same precision (nearest 0.5 °C or 1 °C), readings that match your thermometer with 20 cm³ of solution in the cup, and every change worked out as temperature − initial temperature.
Graph (c), (d)
A y-axis scale that fits your points and uses more than half the grid, a smooth curve of best fit from (0, 0) through each set of points, both curves labelled, and a value read correctly from your curve for solution J.
Conclusions (e) to (g)
The more concentrated solution and why (the larger temperature change), exothermic from the temperature rise, and a prediction for solution J diluted with an equal volume of water.
Evaluation (h) to (j)
The main source of error (heat loss), an improvement with a reason (a lid on the cup), and a safety precaution.
Habits that save marks
Keep stirring. Zinc powder sinks to the bottom of the cup; stirring keeps it in contact with the solution so it reacts quickly and the thermometer reads the whole mixture.
Same precision everywhere: the thermometer has 1 °C divisions, so record every temperature and every change to the nearest 0.5 °C (23.0, 23.5), not a mix of 23 and 23.5.
A curve, not dot-to-dot: the temperature change rises quickly, then levels off and falls slowly as heat escapes. Draw one smooth curve from (0, 0) for each solution and label it.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.