IGCSE Chemistry 0620/52 May/June 2025 Past Paper with Answers

Question 1

A 2.0 g sample of anhydrous lithium chloride is dissolved in distilled water and the highest temperature reached is recorded, so the temperature change can be found for each experiment. Five experiments use 40, 30, 25, 20 then 15 cm³ of water. How should the temperature change vary across the five experiments?

1. the temperature change increases as the volume of water decreases, because the same energy heats a smaller amount of water
2. the temperature change decreases as the volume of water decreases, because there is less water to react with
3. the temperature change stays exactly the same in every experiment, whatever the volume of water
4. the temperature change varies randomly with no link to the volume of water used

Question 2

A student presents the results as a plot of the temperature change (y-axis) against the volume of water (x-axis) for the five experiments. Which approach produces a correctly drawn plot?

1. use a linear y-axis scale so the points extend over half the grid, plot all five points accurately, then draw a single line of best fit
2. use a scale that squeezes all five points into one corner, then join neighbouring points dot-to-dot with short lines
3. use a different sized scale on each half of the y-axis so that the five points spread out across the grid
4. plot only the first and last points and join them with a single straight ruler line through the middle

Question 3

A best-fit line shows how the temperature change varies with the volume of water for volumes from 15 to 40 cm³. How is the temperature change at 45 cm³ of water found from this line?

1. extend the line smoothly beyond the last point to 45 cm³, then read across to the temperature-change axis and give the value in °C
2. read the value where the line crosses the temperature-change axis, ignoring the volume of 45 cm³
3. add together the temperature changes for the 40 cm³ and 30 cm³ experiments and use the total
4. measure the total length of the best-fit line in centimetres and use that number

Question 4 · Answer A

Step 1: Substitute the values into energy = temperature change × 4.2 × volume of water. Step 2: That is 20.0 × 4.2 × 15. Step 3: 20.0 × 4.2 = 84, and 84 × 15 = 1260, so the energy given out is 1260 J.

Question 5 · Answer A

Step 1: The energy released is proportional to the mass of lithium chloride that dissolves. Step 2: Doubling the mass from 2.0 g to 4.0 g doubles the energy given out, and the same volume of water now receives twice the energy. Step 3: So the temperature change roughly doubles, from 10.0 °C to about 20.0 °C.

Question 6 · Answer A

Step 1: Dissolving lithium chloride gives out heat, and some of that heat can escape to the surroundings. Step 2: Polystyrene is a better insulator than glass, so it reduces the heat lost from the cup. Step 3: With less heat lost, the measured temperature change is closer to the true value, so the results are more accurate.

Question 7 · Answer A

Step 1: A burette has finer graduations than a measuring cylinder, so the volume can be read to a smaller division. Step 2: This means the volume of water is measured more precisely. Step 3: So using a burette is an improvement because it measures the volume of water more accurately.

Question 8 · Answer A

Step 1: The whole point of the experiment is to measure the temperature change as the lithium chloride dissolves. Step 2: A water-bath holds the contents at a fixed temperature, so it would cancel out the very temperature change being measured. Step 3: So a water-bath is not an improvement because it would keep the temperature constant.

Question 9 · Answer A

Step 1: Adding sodium hydroxide to an iron(II) salt gives a green precipitate of iron(II) hydroxide. Step 2: Iron(II) hydroxide is insoluble in excess sodium hydroxide, so the precipitate stays when more is added. Step 3: So a green precipitate forms dropwise and it remains insoluble in excess.

Question 10 · Answer A

Step 1: Chlorine is more reactive than iodine, so it displaces iodide ions to form iodine, which colours the solution brown. Step 2: Iodine gives a blue-black colour with starch. Step 3: So the solution turns brown with chlorine and then blue-black when starch is added.

Question 11 · Answer A

Step 1: Acidified silver nitrate gives a precipitate whose colour identifies the halide: white for chloride, cream for bromide, yellow for iodide. Step 2: Solution J contains iodide ions, which give a yellow precipitate. Step 3: So the observation is a yellow precipitate.

Question 12 · Answer A

Step 1: Iron(II) ions react with carbonate ions to form iron(II) carbonate, which is insoluble. Step 2: Iron(II) compounds are green, so the precipitate is green. Step 3: So adding sodium carbonate to solution J gives a green precipitate.

Question 13 · Answer A

Step 1: A green precipitate with sodium hydroxide, insoluble in excess, shows an iron(II) ion. Step 2: A yellow precipitate with silver nitrate shows an iodide ion. Step 3: Combining an iron(II) ion with iodide ions gives iron(II) iodide, $\text{FeI}_2$.

Question 14 · Answer A

Step 1: Each metal ion gives a characteristic flame colour. Step 2: Potassium ions give a lilac flame. Step 3: So the flame colour for solid K is lilac.

Question 15 · Answer A

Step 1: Warming a solution with sodium hydroxide releases ammonia only if ammonium ions are present, and ammonia turns damp red litmus blue. Step 2: Here the litmus stays red, so no ammonia is given off. Step 3: So the observation is no change, with the red litmus paper staying red.

Question 16 · Answer A

Step 1: Ammonium ions release ammonia when warmed with sodium hydroxide, turning damp red litmus blue. Step 2: No ammonia was given off, so the litmus stayed red. Step 3: So the conclusion is that solid K does not contain ammonium ions.

Question 17 · Answer A

Step 1: Aluminium with warm sodium hydroxide reduces nitrate ions to ammonia gas, so bubbles of gas are seen. Step 2: Ammonia is alkaline and turns damp red litmus paper blue. Step 3: So the observations are effervescence and the gas turning damp red litmus paper blue, showing nitrate ions are present.

Question 18 · Answer A

Step 1: A lilac flame shows a potassium ion. Step 2: Producing ammonia with aluminium and warm sodium hydroxide shows a nitrate ion. Step 3: Combining a potassium ion with a nitrate ion gives potassium nitrate, $\text{KNO}_3$.

Question 19 · Answer A

Step 1: Use a measured 100 cm³ of water in a suitable container and heat it to 50 °C, holding it at that temperature so the result is for the stated temperature. Step 2: Add magnesium sulfate in portions with stirring until no more dissolves, so the water is saturated. Step 3: Find the mass that dissolved (for example by filtering or weighing the excess), then state it as grams per 100 cm³ of water, which is the solubility.