Grade 11 Physical Sciences · Chemical Change · Identify oxidising and reducing agents

Oxidising and Reducing Agents Grade 11

Say which substance is oxidised or reduced, or which is the oxidising or reducing agent, and why (zinc loses electrons, so it is oxidised).

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

How To Find The Oxidizing and Reducing AgentThe Organic Chemistry Tutor

Oxidizing Agent vs Reducing Agent (Oxidant vs Reductant)Wayne Breslyn (Dr. B.)

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Question 9.3 · November 2019 · Paper 2 · National (DBE) · 2 marks

The unbalanced equations for two redox reactions, in which

SO_{2}

is involved, are as follows:

Reaction 1:

SO_{2} (g) + H_{2} S (g) \to S (s) + H_{2} O (ℓ)

Reaction 2:

SO_{2} (g) + KMnO_{4} (s) + H_{2} O (ℓ) \to MnSO_{4} (aq) + K_{2} SO_{4} (aq) + H_{2} SO_{4} (aq)

9.3 Is Mn in Reaction 2 OXIDISED or REDUCED? Give a reason for the answer.(2)

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3. Question 1.10 · November 2018 · Paper 2 · National (DBE) · 2 marks
1.10 In which ONE of the following reactions is $HCl$ oxidised?(2)
1. A $HCl(aq) + H_{2} O (ℓ) \to H_{3} O^{+} (aq) + Cl^{-} (aq)$
2. B $CaCO_{3} (s) + 2 HCl(aq) \to CaCl_{2} (aq) + H_{2} O (ℓ) + CO_{2} (g)$
3. C $NH_{3} (aq) + HCl(aq) \to NH_{4} Cl(aq)$
4. D $MnO_{2} (aq) + 4 HCl(aq) \to MnCl_{2} (aq) + H_{2} O (ℓ) + Cl_{2} (g)$
Show the memo (2 ticks)Memo
1. ✓
  Correct optionIn D the oxidation number of Cl increases from $- 1$ (in HCl) to $0$ (in $Cl_{2}$ ), so HCl is oxidised (and Mn is reduced from $+ 4$ to $+ 2$ ). A, B and C are acid-base reactions: no oxidation number changes.
  
  Answer: D
  2 marks · Identify oxidising and reducing agents
4. Question 1.9 · September 2026 · Paper 2 · Provincial · 2 marks
Four options are provided as possible answers to the following questions. Each question has only ONE correct answer. Choose the answer and write only the letter (A–D).
1.9 Magnesium reacts quickly with hot water to form magnesium hydroxide and hydrogen gas, as shown in the equation below:

$Mg(s) + 2 H_{2} O (ℓ) \to Mg(OH)_{2} (aq) + 2 H_{2} (g)$

Which of the following correctly identifies the oxidising agent and reducing agent in the above reaction?(2)
1. A Oxidising agent: $H_{2} O$ ; reducing agent: $H_{2}$
2. B Oxidising agent: $H_{2} O$ ; reducing agent: Mg
3. C Oxidising agent: Mg; reducing agent: $H_{2} O$
4. D Oxidising agent: $Mg(OH)_{2}$ ; reducing agent: Mg
Show the memo (2 ticks)Memo
1. ✓
  Identify the oxidising and reducing agentsMg: oxidation number $0 \to + 2$ , so Mg loses electrons, is oxidised and is the reducing agent.
  H in $H_{2} O$ : $+ 1 \to 0$ in $H_{2}$ , so water gains electrons, is reduced and is the oxidising agent.
  
  Answer: B
  2 marks · Identify oxidising and reducing agents
5. Question 1.9 · November 2025 · Paper 2 · Provincial · 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) in the ANSWER BOOK, for example 1.11 E.
1.9 Consider the reaction below:

5 Zn + 2 $MnO_{4}^{-}$ + 16 $H^{+}$ → 5 $Zn^{2 +}$ + 2 $Mn^{2 +}$ + 8 $H_{2} O$

The reducing agent in the above reaction is ...(2)
1. A Zn
2. B $MnO_{4}^{-}$
3. C $H^{+}$
4. D $Mn^{2 +}$
Show the memo (2 ticks)Memo
1. ✓
  Choose the correct optionZn (oxidation number 0) becomes $Zn^{2 +}$ (+2): Zn loses electrons and is oxidised, so Zn is the reducing agent.
  Mn goes from +7 in $MnO_{4}^{-}$ to +2 in $Mn^{2 +}$ : $MnO_{4}^{-}$ is reduced and is the oxidising agent.
  
  Answer: A
  2 marks · Identify oxidising and reducing agents
6. Question 9.2.1 · November 2025 · Paper 2 · Provincial · 2 marks
A clean piece of aluminium metal strip is placed in a copper sulphate ( $CuSO_{4}$ ) solution. The reaction was observed again after 2 hours.

After 2 hours it was observed that the blue solution turned colourless and the shiny metallic aluminium turned brown.

The net ionic balanced equation for the reaction is given below:

$2 Al (s) + 3 Cu^{2 +} (aq) \to 3 Cu (s) + 2 Al^{3 +} (aq)$
9.2 Write down the chemical symbol of a substance that is ...
9.2.1 oxidised.(2)
Show the memo (2 ticks)Memo
1. ✓
  Substance oxidisedAl
  2 marks · Identify oxidising and reducing agents

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