Grade 11 Physical Sciences · Chemical Change · Paper 2 (Chemistry)

Redox Reactions Grade 11

Real Redox Reactions past paper questions from 2018 to 2021 and practice questions, with each memo split into the ticks examiners give. Try one, mark yourself, and see exactly which skill cost you marks.

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Question 1.10 · November 2019 · Paper 2 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10). Each question has only ONE correct answer.

1.10 Oxidation takes place when the ...(2)

A reducing agent loses electrons.
B oxidising agent loses electrons.
C reducing agent gains electrons.
D oxidising agent gains electrons.

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More Redox Reactions Grade 11 questions and answers

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4. Question 9.1 · November 2018 · Paper 2 · National (DBE) · 2 marks
The reaction between permanganate ions ( $MnO_{4}^{-}$ ) and hydrogen sulphide ( $H_{2} S$ ) is given below.

$MnO_{4}^{-} (aq) + H^{+} (aq) + H_{2} S(g) \to Mn^{2 +} (aq) + S(s) + H_{2} O (ℓ)$
9.1 Define reduction in terms of oxidation numbers.(2)
Show the memo (2 ticks)Memo
1. ✓
  Definition of reductionReduction is a decrease in oxidation number.
  2 marks · Define redox and cell terms
5. Question 1.6 · November 2021 · Paper 2 · Provincial · 2 marks
Four options are provided as possible answers to the following questions. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10). Each question has only ONE correct answer.
1.6 The strongest oxidising agent is ...(2)
1. A $KMnO_{4}$ .
2. B $MnO_{2}$ .
3. C $HNO_{3}$ .
4. D $O_{2}$ .
Show the memo (2 ticks)Memo
1. ✓
  Correct optionOn the table of standard reduction potentials the strongest oxidising agent has the most positive reduction potential:
  $MnO_{4}^{-}$ (from $KMnO_{4}$ ): $+ 1, 51$ V
  $MnO_{2}$ : $+ 1, 23$ V
  $O_{2}$ (acid): $+ 1, 23$ V
  $NO_{3}^{-}$ (from $HNO_{3}$ ): $+ 0, 96$ V
  
  Answer: A
  2 marks · Identify oxidising and reducing agents
6. Question 7.1 · November 2021 · Paper 2 · Provincial · 2 marks
In the Haber process, nitrogen (extracted from the air) and hydrogen (obtained from natural gas) are pumped through pipes. The pressure of the mixture of gases is increased to $200$ atmospheres. The pressurised gases are heated to $450$ °C and passed through a tank containing an iron catalyst, to form ammonia ( $NH_{3}$ ), according to the following balanced equation:

$N_{2} + 3 H_{2} \to 2 NH_{3}$
7.1 Define the term oxidation in terms of electron transfer.(2)
Show the memo (2 ticks)Memo
1. ✓
  Definition of oxidationA loss of electrons
  2 marks · Define redox and cell terms
7. Practice · Siyavula Grade 11 Physical Sciences · Ex 14.1 · 3 marks
In Mapungubwe (in the Limpopo Province) there is evidence of gold mining in South Africa as early as 1200. Today, South Africa is a world leader in the technology of gold mining. The following flow diagram illustrates some of the most important steps in the recovery of gold from its ore.
(3) Use oxidation numbers to explain your answer to the question above.(3)
Show the memo (3 ticks)Memo
1. ✓
  Oxidation number of Au in the reactants $4 Au + 8 NaCN + O_{2} + 2 H_{2} O \to 4 NaAu(CN)_{2} + 4 NaOH$
  In the reactants gold has an oxidation number of $0$ .
  1 mark · Assign oxidation numbers
2. ✓
  Oxidation number of Au in the productsIn $NaAu(CN)_{2}$ : $Na^{+}$ is $+ 1$ and $CN^{-}$ is $- 1$ . Let gold be $x$ :
  $+ 1 + x + 2 (- 1) = 0$
  $x = + 1$
  1 mark · Assign oxidation numbers
3. ✓
  ConclusionThe oxidation number of gold increases from $0$ to $+ 1$ , so gold has lost electrons and is oxidised.
  1 mark · Identify oxidising and reducing agents
Question and solution adapted from Siyavula Education (CC BY 3.0)
8. Practice · Siyavula Grade 11 Physical Sciences · Ex 13.7 · 2 marks
Compare the oxidation numbers of:
(a) nitrogen in: $NO_{2}$ and $NO$ (2)
Show the memo (2 ticks)Memo
1. ✓
  First compound $NO_{2}$ : $x + 2 (- 2) = 0 \Rightarrow + 4$
  1 mark · Assign oxidation numbers
2. ✓
  Second compound $NO$ : $x - 2 = 0 \Rightarrow + 2$
  1 mark · Assign oxidation numbers
Question adapted from Siyavula Education (CC BY 3.0) · Solution by NavyBlue
9. Practice · Siyavula Grade 11 Physical Sciences · Ex 13.7 · 3 marks
Give the oxidation numbers for each of the elements in all the compounds. State if there is any difference between the oxidation number of the element in the reactant and the element in the product.
(a) $C(s) + O_{2} (g) \to CO_{2} (g)$ (3)
Show the memo (3 ticks)Memo
1. ✓
  ReactantsC: $0$ ; O in $O_{2}$ : $0$
  1 mark · Assign oxidation numbers
2. ✓
  ProductIn $CO_{2}$ : C $+ 4$ , O $- 2$
  1 mark · Assign oxidation numbers
3. ✓
  ChangeCarbon increases from 0 to +4 (oxidised); oxygen decreases from 0 to −2 (reduced).
  1 mark · Identify oxidising and reducing agents
Question adapted from Siyavula Education (CC BY 3.0) · Solution by NavyBlue
10. Practice · Siyavula Grade 11 Physical Sciences · Ex 13.8 · 2 marks
Consider the following chemical equations: $Fe(s) \to Fe^{2 +} (aq) + 2 e^{-}$ and $4 H^{+} (aq) + O_{2} (g) + 4 e^{-} \to 2 H_{2} O(l)$ . Which one of the following statements is correct?
A. $Fe$ is oxidised and $H^{+}$ is reduced
B. $Fe$ is reduced and $O_{2}$ is oxidised
C. $Fe$ is oxidised and $O_{2}$ is reduced
D. $Fe$ is reduced and $H^{+}$ is oxidised
(DoE Grade 11 Paper 2, 2007)(2)
Show the memo (2 ticks)Memo
1. ✓
  AnswerC: Fe loses electrons (oxidised) and $O_{2}$ gains electrons, its oxidation number going from 0 to −2 (reduced).
  2 marks · Identify oxidising and reducing agents
Question adapted from Siyavula Education (CC BY 3.0) · Solution by NavyBlue

Redox Reactions Grade 11 videos

Short lessons from South African teachers first. Videos load only when you tap play, to save your data.

Redox reactions grade 11 Chemistry: Introduction and OverviewMiss Martins Maths and Science

Redox reactions: Assigning oxidation numbers Grade 11 ChemistryMiss Martins Maths and Science

Redox Reactions Grade 11 Exam Questions Part 1Miss Martins Maths and Science

Electrochemistry How to Use Table 4B for Galvanic Cells | Grade 12 ChemistryMiss Martins Maths and Science

Galvanic Cell Electrochemistry: Net Overall Cell Reaction | Grade 12 ChemistryMiss Martins Maths and Science

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