Edexcel International A Level Chemistry
Edexcel International A Level Chemistry Redox Chemistry Exam Questions
Free Edexcel International A Level Chemistry exam questions for Redox Chemistry, with a mark scheme for every pack. Covers oxidation and reduction, oxidation numbers, naming compounds with oxidation numbers, half-equations, combining ionic equations and disproportionation.
Redox Chemistry exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel International A Level Chemistry Redox Chemistry
Redox chemistry in Unit 2 of Edexcel International A Level Chemistry gives you the tools to analyse any oxidation and reduction reaction. You assign oxidation numbers, use them to name compounds such as iron(III) chloride and potassium manganate(VII), and identify oxidising and reducing agents. You also learn to write half-equations and combine them into balanced ionic equations, including for reactions in acidic solution. The topic is applied straight away to the Group 1, 2 and 7 elements, and is developed in Unit 5 Redox equilibria. Examiners often ask for oxidation numbers in unfamiliar species and for balanced equations built from half-equations.
What you need to know
- Definitions Oxidation is loss of electrons or an increase in oxidation number. Reduction is gain of electrons or a decrease in oxidation number. An oxidising agent accepts electrons and is itself reduced.
- Oxidation number rules Elements are 0; oxygen is usually -2 (but -1 in peroxides); hydrogen is usually +1 (but -1 in metal hydrides); the sum of oxidation numbers equals the charge on the species.
- Naming with oxidation numbers Roman numerals show the oxidation number of an element that can vary, for example iron(II) sulfate, sodium chlorate(I) and potassium dichromate(VI).
- Half-equations Balance the main atoms, add H2O to balance oxygen, add H+ to balance hydrogen, then add electrons to balance charge, for example MnO4- + 8H+ + 5e- gives Mn2+ + 4H2O.
- Combining half-equations Multiply each half-equation so the electrons cancel, add them, then cancel any species that appear on both sides.
- Disproportionation A reaction in which the same element is simultaneously oxidised and reduced, such as chlorine with sodium hydroxide or copper(I) in aqueous solution.
Common mistakes in Redox Chemistry
- Giving oxidation numbers without a sign or with the sign after the number. Write +7, not 7 or 7+.
- Assuming oxygen is always -2. In hydrogen peroxide it is -1.
- Leaving electrons in the final combined equation. They must cancel completely.
- Calling the species that is oxidised the oxidising agent. The species that is oxidised is the reducing agent.
- Not checking that both atoms and charges balance in a half-equation.
Try three Redox Chemistry exam-style questions
1. State the oxidation number of manganese in MnO4- and of chromium in Cr2O7 2-. (2 marks)
Show the mark scheme answer
Mn is +7; Cr is +6.
2. Combine the half-equations MnO4- + 8H+ + 5e- gives Mn2+ + 4H2O and Fe2+ gives Fe3+ + e- to give an overall ionic equation. (2 marks)
Show the mark scheme answer
Multiply the iron half-equation by 5; MnO4- + 8H+ + 5Fe2+ gives Mn2+ + 4H2O + 5Fe3+.
3. Write a half-equation for the reduction of dichromate(VI) ions to chromium(III) ions in acidic solution. (2 marks)
Show the mark scheme answer
Cr2O7 2- + 14H+ + 6e- gives 2Cr3+ + 7H2O; correct species with balanced atoms and charge.
Redox Chemistry FAQs
What does Edexcel International A Level Chemistry Redox chemistry cover?
It covers definitions of oxidation and reduction, oxidation number rules, naming compounds with oxidation numbers, writing and combining half-equations and disproportionation.
Which unit is Redox chemistry examined in?
Redox chemistry is part of Unit 2, and it is developed in Unit 5 with electrode potentials and redox titrations.
How do I get better at half-equations?
Follow the same routine every time (balance atoms, add water, add H+, add electrons) and practise with manganate(VII), dichromate(VI), thiosulfate and halogen examples.
