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IGCSE Combined Science 0653 · Chemistry · 22

0653.C3.1.03 — Deduce the formula of a simple molecular 6 Deduce the formula of an ionic compound compound from the relative numbers of from the relative n: past paper questions

7 real questionsasked in 2 of the last 10 exam series2025–2025usually: Deduce, Explain, Write, State

Real questions on 0653.c3.1.03 — deduce the formula of a simple molecular 6 deduce the formula of an ionic compound compound from the relative numbers of from the relative n

The newest 7 of 7 written questions. Open one to see it on the real paper.

  1. 0653/32 · October/November 2025 · Q5a(i)[1]

    Deduce the molecular formula of the organic compound shown in Fig. 5.1.

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  2. 0653/32 · October/November 2025 · Q5a(ii)[1]

    Explain why the organic compound shown in Fig. 5.1 is not a hydrocarbon.

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  3. 0653/32 · October/November 2025 · Q6a(i)[2]

    Write a number in each gap to complete the sentence.

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  4. 0653/33 · October/November 2025 · Q5a(i)[1]

    Deduce the molecular formula of the organic compound shown in Fig. 5.1.

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  5. 0653/31 · May/June 2025 · Q1c(i)[2]

    State the letter on Fig. 1.2 that represents: combustion

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  6. 0653/31 · May/June 2025 · Q5e[1]

    Fig. 5.1 shows the structure of a compound of magnesium. Br H H Mg C C H H C C H H H Fig. 5.1 Deduce the molecular formula of this compound.

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  7. 0653/42 · May/June 2025 · Q5b(i)[1]

    The ions in calcium hydroxide are Ca 2+ and OH – . Deduce the formula for calcium hydroxide.

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What examiners said

This question was well answered by most candidates who correctly interpreted the flow diagram of the carbon cycle.

— Examiner report, May/June 2025, 0653/31 Q1(c)(i) (Cambridge)

The different elements had to be grouped together to get a total for each type. Many candidates did this successfully. Others grouped the elements correctly but then put + signs between each one. Therefore, instead of the correct formula C4H7MgBr, they wrote C4 + H7 + Mg + Br, and these answers were not acceptable. The elements could be written in any order as long as the numbers of atoms of each...

— Examiner report, May/June 2025, 0653/31 Q5(e) (Cambridge)

Few candidates remembered to place (OH) inside brackets when stating the formula for calcium hydroxide.

— Examiner report, May/June 2025, 0653/42 Q5(b)(i) (Cambridge)

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0653.C3.1.03 — Deduce the formula of a simple molecular 6 Deduce the formula of an ionic compound compound from the relative numbers of from the relative n — IGCSE Combined Science 0653 past paper questions | AssessPro