IGCSE Chemistry 0620/63 May/June 2025 Past Paper with Answers

Question 1

In a fermentation experiment, aqueous glucose and yeast are placed in a container A that stands in a water-bath, and the carbon dioxide produced is collected in an apparatus B that measures the volume of gas. What are the names of apparatus A and B?

1. A is a conical flask and B is a gas syringe
2. A is a beaker and B is a measuring cylinder
3. A is a boiling tube and B is a burette
4. A is a round-bottomed flask and B is a thermometer

Question 2

In a fermentation experiment the conical flask of glucose and yeast stands in a water-bath. Why is the water-bath used?

1. to keep the mixture warm (about 25 degrees C to 35 degrees C) so fermentation can take place
2. to cool the mixture so that the yeast stops reacting
3. to boil the mixture so the ethanol evaporates straight away
4. to keep the mixture at exactly 100 degrees C

Question 3

In a fermentation experiment the volume of carbon dioxide collected is recorded every 10 minutes up to 90 minutes. The recorded volume is still rising at 90 minutes. How do the results show that fermentation is NOT complete after 90 minutes?

1. the volume of gas collected is still increasing at 90 minutes and has not become constant
2. the volume of gas collected stays exactly the same throughout
3. no gas at all has been collected by 90 minutes
4. the volume of gas collected falls back to zero at 90 minutes

Question 4 · Answer A

Step 1: Carbon dioxide is the gas produced by fermentation. Step 2: Carbon dioxide reacts with limewater to form insoluble calcium carbonate. Step 3: The fine white solid makes the limewater turn milky (cloudy white), which is the positive test for carbon dioxide.

Question 5 · Answer A

Step 1: While fermentation continues, carbon dioxide is given off and bubbles pass through the limewater. Step 2: When fermentation is complete, no more carbon dioxide is produced. Step 3: So the observation is that no more bubbles of gas are produced.

Question 6 · Answer A

Step 1: Ethanol and water are miscible liquids with different boiling points (ethanol boils at about 78 degrees C, water at 100 degrees C). Step 2: Distillation separates liquids by their different boiling points, so the ethanol vaporises first and is condensed and collected. Step 3: Filtration only removes insoluble solids, and crystallisation and chromatography do not separate these two liquids, so distillation is used.

Question 7 · Answer A

Step 1: The thiosulfate plus water must total 50 cm3 each time (50 + 0 in Experiment 1). Step 2: With 40 cm3 of thiosulfate, the distilled water must be 50 - 40 = 10 cm3. Step 3: The dilute hydrochloric acid is kept the same at 5 cm3 in every experiment, so the recorded values are 10 cm3 of water and 5 cm3 of acid.

Question 8 · Answer A

Step 1: A good graph uses a linear scale that spreads the plotted points over more than half of the grid so the trend is clear. Step 2: Every point must be plotted accurately. Step 3: A single smooth curve of best fit is then drawn through the points, rather than joining them dot-to-dot or using only two of them.

Question 9 · Answer A

Step 1: Relative rate = 1 / time. Step 2: With a time of 30 s, relative rate = 1 / 30. Step 3: 1 / 30 = 0.033 (to 2 significant figures), with no units.

Question 10 · Answer A

Step 1: Relative rate = 1 / time, so the shortest time gives the greatest rate. Step 2: Experiment 1 has the shortest time (30 s). Step 3: Therefore Experiment 1 has the greatest relative rate of reaction.

Question 11 · Answer A

Step 1: The thiosulfate and water must add up to 50 cm3. Step 2: Volume of water = 50 - 37. Step 3: 50 - 37 = 13 cm3 of distilled water (the unit cm3 is needed for the second mark).

Question 12 · Answer A

Step 1: To read a value off a curve, draw a vertical construction line from 37 cm3 up to the best-fit curve. Step 2: Then draw a horizontal line across to the time axis and read the value. Step 3: Because 37 cm3 lies just below 40 cm3 (37 s), the reading is a little more, about 40 s, and the construction lines must be shown.

Question 13 · Answer A

Step 1: Only the thiosulfate concentration is meant to change between experiments. Step 2: Keeping the total volume the same keeps the depth of liquid and the concentration of the acid in the final mixture the same each time. Step 3: This makes the comparison fair, so any change in time is due only to the thiosulfate concentration.

Question 14 · Answer A

Step 1: A burette has finer, more closely spaced graduations than a measuring cylinder. Step 2: This lets the volume be measured to a smaller division and read more precisely. Step 3: So a burette improves the experiment because it measures the volume more accurately.

Question 15 · Answer A

Step 1: A volumetric pipette is made to deliver one single, fixed volume. Step 2: The thiosulfate volume changes from experiment to experiment (50, 40, 30, 25, 20 cm3). Step 3: One fixed-volume pipette cannot measure all these different volumes, so it cannot be used.

Question 16 · Answer A

Step 1: You judge the time by how long the printed text stays visible through the depth of solution. Step 2: A larger beaker would spread the same volume over a wider base, changing the depth of liquid you look through. Step 3: A different depth changes the time measured for the text to disappear, so the comparison between experiments would no longer be fair.

Question 17 · Answer A

Step 1: Aluminium ions give a white precipitate of aluminium hydroxide when sodium hydroxide is added dropwise. Step 2: Aluminium hydroxide is amphoteric, so it dissolves in excess sodium hydroxide to give a colourless solution. Step 3: So the observations are a white precipitate that dissolves in excess.

Question 18 · Answer A

Step 1: Aluminium ions give a white precipitate of aluminium hydroxide with aqueous ammonia added dropwise. Step 2: In excess ammonia the aluminium hydroxide does not dissolve. Step 3: So the precipitate forms and then remains (is insoluble) in excess ammonia.

Question 19 · Answer A

Step 1: Acidified silver nitrate is the test for halide ions. Step 2: Chloride ions give a white precipitate of silver chloride. Step 3: A cream precipitate would mean bromide and a yellow precipitate iodide, so chloride gives a white precipitate.

Question 20 · Answer A

Step 1: Acidified barium nitrate gives a white precipitate of barium sulfate only when sulfate ions are present. Step 2: Aluminium chloride contains no sulfate ions. Step 3: With no sulfate present, no precipitate forms, so no change is seen.

Question 21 · Answer A

Step 1: Warming a solution with sodium hydroxide and aluminium foil reduces nitrate ions to ammonia. Step 2: Ammonia is the only common gas that turns damp red litmus paper blue. Step 3: So the gas given off is ammonia.

Question 22 · Answer A

Step 1: A light green flame colour indicates barium ions, confirmed by the white precipitate of barium sulfate with sulfuric acid. Step 2: Giving off ammonia when warmed with sodium hydroxide and aluminium foil indicates nitrate ions. Step 3: A solid containing barium ions and nitrate ions is barium nitrate.

Question 23 · Answer A

Step 1: Because lead(II) chloride is insoluble, it is made by precipitation: dissolve the sodium chloride and lead(II) nitrate separately in distilled water and mix the solutions, so insoluble lead(II) chloride precipitates. Step 2: Filter the mixture to collect the lead(II) chloride as the residue, leaving the soluble sodium nitrate in the filtrate. Step 3: Wash the residue with distilled water to remove the soluble salt, then leave it to dry, giving a pure dry sample.