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3.1 Introducing chemical reactions

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Question 7

Chromium powder is heated in oxygen. Analysis of the solid product identifies Cr3+\mathrm{Cr^{3+}}Cr3+ ions and O2−\mathrm{O^{2-}}O2− ions.

What is the balanced symbol equation for this reaction?

[1]
A

4Cr+3O2→2Cr2O3\mathrm{4Cr + 3O_{2} \rightarrow 2Cr_{2}O_{3}}4Cr+3O2​→2Cr2​O3​

B

3Cr+O2→Cr3O2\mathrm{3Cr + O_{2} \rightarrow Cr_{3}O_{2}}3Cr+O2​→Cr3​O2​

C

2Cr+O2→2CrO\mathrm{2Cr + O_{2} \rightarrow 2CrO}2Cr+O2​→2CrO

D

2Cr+3O2→Cr2O3\mathrm{2Cr + 3O_{2} \rightarrow Cr_{2}O_{3}}2Cr+3O2​→Cr2​O3​

Markscheme

3.1 Introducing chemical reactions Questions

  1. GCSE
  2. /Chemistry
  3. /3.1 Introducing chemical reactions

134 exam-style questions on OCR GCSE Chemistry 3.1 Introducing chemical reactions, covering 3.1.1 Writing formulae and balanced chemical equations, 3.1.2 Formulae of compounds from ions, and state symbols, 3.1.3 Conservation of mass and observed changes in mass, 3.1.4 Half equations and balanced ionic equations, 3.1.5 The mole and the Avogadro constant, and 3.1.6 Stoichiometry, limiting reactants and reacting masses. Each one has a worked solution and a mark scheme showing where the marks go.

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