CAIE A-Level Chemistry AS 6.1.1 Oxidation Numbers of Elements in Compounds Questions

Practise calculating oxidation numbers and identifying oxidation-state changes in compounds, ions and redox reactions using CAIE 9701 AS questions.

Exam points

Calculate and assign oxidation numbers to elements in compounds and ions, including changes in redox reactions.

[Maximum number: 1]

Sodium chromate(VI), $\mathrm{Na}_{2} \mathrm{CrO}_{4}$ , is manufactured by heating chromite, $\mathrm{FeCr}_{2} \mathrm{O}_{4}$ , with sodium carbonate in an oxidising atmosphere. Chromite contains $\mathrm{Cr}_{2} \mathrm{O}_{4}{ }^{2-}$ ions.

2 \mathrm{FeCr}_{2} \mathrm{O}_{4}+4 \mathrm{Na}_{2} \mathrm{CO}_{3}+3 \frac{1}{2} \mathrm{O}_{2} \rightarrow 4 \mathrm{Na}_{2} \mathrm{CrO}_{4}+\mathrm{Fe}_{2} \mathrm{O}_{3}+4 \mathrm{CO}_{2}

What happens in this reaction?

Chromium and iron are the only elements oxidised.

Chromium, iron and carbon are oxidised.

Only chromium is oxidised.

Only iron is oxidised.

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CAIE A-Level Chemistry AS 6.1.1 Oxidation Numbers of Elements in Compounds Questions question 1