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CAIE A-Level Chemistry 6.1 Redox and Oxidation Numbers

Practise identifying oxidation and reduction through electron transfer or oxidation-number change and balancing redox equations.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • assign oxidation numbers using charge-sum rules and identify which element changes
  • define oxidation as electron loss or oxidation-number increase and reduction as gain or decrease
  • identify oxidising and reducing agents and combine half-equations with equal electron transfer

Covered syllabus points

6.1.1—Oxidation numbers of elements in compounds6.1.2—Changes in oxidation numbers to help balance6.1.3 Redox Terminology6.1.4—And use the terms oxidising agent and reducing6.1.5 Oxidation Numbers in Compound Names

6.1 Redox: electron transfer and oxidation number question 1

[Maximum number: 2]

Nitrogen and phosphorus are elements in Group 15 of the Periodic Table.

Question (a)

(a)

A common test for nitrates is the reaction with NaOH and Al . Equation 1 shows the reaction.

 equation 13NO3−+8Al+5OH−+18H2O→3NH3+8[Al(OH)4]−\text { equation } 1 \quad 3 \mathrm{NO}_{3}^{-}+8 \mathrm{Al}+5 \mathrm{OH}^{-}+18 \mathrm{H}_{2} \mathrm{O} \rightarrow 3 \mathrm{NH}_{3}+8\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}
[ 2 ]

Question (i)

(i)

Deduce the oxidation state of nitrogen in NO3−\mathrm{NO}_{3}^{-}.

[ 1 ]

Question (ii)

(ii)

Identify the species that is oxidised in equation 1.

[ 1 ]

6.1 Redox: electron transfer and oxidation number question 2

[Maximum number: 1]

Chlorine is a reactive element. It forms many compounds.

Bleach is used as a cleaning product to kill bacteria. It is made by adding compounds like sodium chlorate(I), NaClO, to water.

Sodium chlorate(I), NaClO, reacts with hydrogen peroxide to produce sodium chloride, water and oxygen gas.

Construct an equation for this reaction.

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