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O Level Chemistry 5070 Paper 42, May/June 2026

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Question paper

5070/42 · May/June 2026

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1

Figure 1.1 shows the apparatus a student uses to separate a mixture of three different alkanes.

Figure 1 of 1 for question 1
a(i)

State the name of apparatus A.

[1]
a(ii)

Explain how apparatus A works.

[1]
b

State the property that allows the alkanes to be separated by this method.

[1]
c

Describe how the three different alkanes are obtained from the mixture.

[3]
2

A student investigates the effect of concentration on the rate of reaction between calcium carbonate and dilute hydrochloric acid. calcium carbonate+hydrochloric acid→calcium chloride+water+carbon dioxide (a) The student does five experiments using 2.00 mol/dm3 hydrochloric acid, B. Experiment 1 The student: • uses a measuring cylinder to add 50 cm3 of B to a conical flask • puts the conical flask on a piece of black paper • adds 1 g of calcium carbonate to the flask • immediately starts the stop-watch • observes the reaction by looking down into the flask from above • stops the stop-watch when the reaction is complete • records in Table 2.1 the time taken for the reaction to complete. Experiments 2–5 The student repeats the experiment four times but instead of 50 cm3 of B uses different volumes of B and distilled water as shown in Table 2.1.

Figure 1 of 1 for question 2
a(i)

Suggest an observation that shows when the reaction is complete.

[1]
a(ii)

Plot on the grid the time taken (y-axis) against volume of B (x-axis). Label the axes.

[3]
a(iii)

Draw a curve of best fit.

[1]
a(iv)

Use the graph to deduce the time taken when 25 cm3 of B and 25 cm3 of distilled water are used. time ....................................................... s

[1]
b

Measuring the mass of the calcium carbonate and the precision of the stop-watch are sources of inaccuracy in these experiments. Suggest two other sources of inaccuracy in these experiments. Suggest an improvement that reduces each of these sources of inaccuracy. source of inaccuracy ................................................................................................................. ................................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... source of inaccuracy ................................................................................................................. ................................................................................................................................................... improvement ............................................................................................................................. ...................................................................................................................................................

[4]
c(i)

The concentration of hydrochloric acid in B is 2.00 mol/dm3. Calculate the concentration of the hydrochloric acid in the flask before the calcium carbonate is added in experiment 3. concentration .......................................... mol/dm3

[1]
c(ii)

State the relationship between the concentration of hydrochloric acid and the rate of reaction. Explain how the data in Table 2.1 shows this relationship. relationship ........................................................................................................................ ........................................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... ...........................................................................................................................................

[3]
3

A student investigates a pink solid, C, which contains two cations and one anion. (a) The student: • puts some C into a boiling tube • clamps the boiling tube as shown in Figure 3.1 • heats C • observes any changes that take place.

Figure 1 of 2 for question 3
Figure 2 of 2 for question 3
a(i)

Suggest a possible safety hazard and a precaution to take to minimise the hazard when using the apparatus in Figure 3.1. hazard ............................................................................................................................... precaution ......................................................................................................................... ...........................................................................................................................................

[2]
a(ii)

State the name of the piece of apparatus used to heat solid C.

[1]
a(iii)

C turns into a yellow solution that becomes a yellow solid on further heating. State two conclusions made from these observations. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ...........................................................................................................................................

[2]
a(iv)

Ammonia gas is given off when C is heated with aqueous sodium hydroxide. Describe the effect of ammonia gas on damp red and damp blue litmus papers. Suggest a conclusion about solid C that is made from these observations. damp red litmus ................................................................................................................. damp blue litmus ............................................................................................................... conclusion ......................................................................................................................... ...........................................................................................................................................

[3]
b(i)

The student dissolves C in water. A pale yellow aqueous solution of C is formed. The student determines the pH of aqueous C but does not use a pH meter. Describe how the student determines the pH of aqueous C.

[1]
b(ii)

Aqueous C has a pH of 2. Describe the observation the student makes when determining this pH.

[1]
b(iii)

A few drops of aqueous sodium hydroxide are added to aqueous C. Excess aqueous sodium hydroxide is then added. The student concludes that iron(III) ions are present in C. Describe the observations that the student makes.

[2]
b(iv)

Dilute nitric acid and aqueous barium nitrate are added to aqueous C. The student thinks that a yellow precipitate is formed. The mixture is left for five minutes to allow the precipitate to settle. The student then sees that the precipitate is white, not yellow. Explain why the precipitate appears yellow at first but is seen to be white after it settles.

[1]
b(v)

State a conclusion that is made from the observations in 3(b)(iv).

[1]
4

Aqueous ammonia is an alkaline solution that is used to clean surfaces. The higher the concentration of aqueous ammonia, the better it is at cleaning surfaces. A student investigates three different samples of aqueous ammonia. Plan an investigation to determine the concentration of ammonia in each of the three samples. Your plan should describe the use of common laboratory apparatus, dilute hydrochloric acid, a suitable indicator and the three samples of aqueous ammonia. No other chemicals should be used. Your plan should include: • the apparatus needed • the method to use • how to use the results to show which sample is the best at cleaning surfaces. You do not need to show any calculations. You may draw a diagram to help answer the question.

[6]

Mark scheme

5070/42 · May/June 2026

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1a(i) · 1 mark

  • 1 mark

    (Liebig) condenser

1a(ii) · 1 mark

  • 1 mark

    (the water) cools (the gas/vapour)/reduces the temperature

1b · 1 mark

  • 1 mark

    (Different) boiling point

1c · 3 marks

  • M1

    (collect the first liquid) when the temperature becomes constant/first boiling point reached

  • M2

    replace the conical flask

  • M3

    collect the next alkane when the temperature is constant again/when its boiling point is reached

2a(i) · 1 mark

  • 1 mark

    Effervescence/bubbles/fizzing stops/all solid reacted/all solid disappears/no solid remains

2a(ii) · 3 marks

  • M1

    both axes labelled with units

  • M2

    Suitable scale for time using at least half of the grid.

  • M3

    Points plotted correctly within +/– half a small square.

2a(iii) · 1 mark

  • 1 mark

    Appropriate curve of best fit

2a(iv) · 1 mark

  • 1 mark

    Value recorded correctly to +/– half a small square.

2b · 4 marks

  • 1 mark

    Source 1: measuring volumes (of water or acid) / judging when all solid has reacted/reaction has ended / clumping of solid in flask / Temperature variation

  • 1 mark

    Improvement 1: linked improvement for source 1

  • 1 mark

    Source 2: a second valid source from the list

  • 1 mark

    Improvement 2: linked improvement for source 2

2c(i) · 1 mark

  • 1 mark

    1.4 mol / dm3

2c(ii) · 3 marks

  • M1

    the greater the concentration the greater the rate or reverse argument

  • M2

    the less volume of acid used/the more water used the lower the concentration (ORA)

  • M3

    the shorter the time the greater the rate (ORA)

3a(i) · 2 marks

  • M1

    solid spitting out of tube

  • M2

    keep flame moving/warm gently/pointing tube away from people/wear safety goggles

3a(ii) · 1 mark

  • 1 mark

    Bunsen (burner)

3a(iii) · 2 marks

  • M1

    Solid/ C (may contain) a transition metal (ion)

  • M2

    Solid/ C (may contain) water (of crystallisation)/C is hydrated/C becomes anhydrous/C loses water when heated

3a(iv) · 3 marks

  • M1

    red litmus turns blue

  • M2

    blue litmus does not change /no change/stays the same

  • M3

    Solid contains ammonium/NH4+ (ions)

3b(i) · 1 mark

  • 1 mark

    Use universal indicator

3b(ii) · 1 mark

  • 1 mark

    Correct colour change for the indicator stated in 3(b)(i) e.g. (Universal indicator) turns red/orange

3b(iii) · 2 marks

  • M1

    Red-brown precipitate.

  • M2

    Insoluble in excess

3b(iv) · 1 mark

  • 1 mark

    Yellow solution makes the white precipitate look yellow

3b(v) · 1 mark

  • 1 mark

    Sulfate ions/SO42–

4 · 6 marks

  • 1 mark

    Apparatus: Uses a burette and pipette.

  • 1 mark

    Method: Adds dilute hydrochloric acid to aqueous ammonia (ORA).

  • 1 mark

    Method: Suggests a named suitable indicator / The acid is added to the aqueous ammonia until indicator/it changes colour (ORA).

  • 1 mark

    Method: Takes an initial and final burette reading.

  • 1 mark

    Method: Repeats and takes an average (of concordant results) with same sample of ammonia OR adds acid dropwise and swirling/mixing/stirring / Repeats with the other two samples of aqueous ammonia.

  • 1 mark

    Conclusion: If acid is in the burette: The cleaner which needs the highest volume of acid is the most effective/has the highest concentration (ORA). OR If ammonia is in the burette: The cleaner which needs the lowest volume of ammonia is the most effective/has the highest concentration (ORA).

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