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CAIE IGCSE Chemistry 3.1.8 Deduce the symbol equation with state

Practise deducing balanced symbol equations from reaction descriptions, including salts, oxides, extraction and decomposition.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • convert a worded reaction pathway into correct formulae for products
  • balance full symbol equations after deducing missing products or hydrocarbon formulae

3.1.8—Deduce the symbol equation with state question 1

[Maximum number: 2]

25 cm325 \mathrm{~cm}^{3} of a gaseous hydrocarbon, CxHy\mathrm{C}_{x} \mathrm{H}_{y}, were burnt in 150 cm3150 \mathrm{~cm}^{3} of oxygen. This was an excess of oxygen.

After cooling, the volume of the gases remaining was 100 cm3100 \mathrm{~cm}^{3}. This consisted of 75 cm375 \mathrm{~cm}^{3} of carbon dioxide and 25 cm325 \mathrm{~cm}^{3} of unreacted oxygen. The water that was produced in the reaction was liquid.

All volumes were measured at the same temperature and pressure.

Use your answer to (b)(iii) to balance the chemical equation. Deduce the formula of the hydrocarbon.

CxHy( g)+…….O2( g)→…….CO2( g)+…….H2O(l)\mathrm{C}_{x} \mathrm{H}_{y}(\mathrm{~g})+\ldots \ldots . \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \ldots \ldots . \mathrm{CO}_{2}(\mathrm{~g})+\ldots \ldots . \mathrm{H}_{2} \mathrm{O}(\mathrm{l})
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