Grade 11 Physical Sciences · Chemical Change · Combine half-reactions into net equation

Redox Reactions Grade 11

Combine two half-reactions so the electrons cancel to give the balanced overall reaction (Zn + Cu²⁺ → Zn²⁺ + Cu).

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

How to Balance Redox Equations in Acidic SolutionTyler DeWitt

Balancing Redox Reactions in Acidic and Basic ConditionsProfessor Dave Explains

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Question 9.6 · November 2019 · Paper 2 · National (DBE) · 4 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)

9.6 Use the Table of Standard Reduction Potentials and write down the balanced net ionic equation for Reaction 1. Show the half-reactions and how you arrived at the final equation.(4)

Work it out on paper first. Then mark yourself with the official memo, one tick at a time.

More past paper questions: combine half-reactions into net equation

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3. Question 8.2.1 · November 2024 · Paper 2 · National (DBE) · 3 marks
8.2 A galvanic cell is represented by the following cell notation:

$Pb(s) ∣ Pb^{2 +} (aq) ∥ Fe^{3 +} (aq), Fe^{2 +} (aq) ∣ Pt(s)$

Answer the questions that follow.
8.2.1 Write down the balanced net ionic equation for this cell.(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactants $Pb(s) + 2 Fe^{3 +} (aq)$
  1 mark · Combine half-reactions into net equation
2. ✓
  Products $\to Pb^{2 +} (aq) + 2 Fe^{2 +} (aq)$
  1 mark · Combine half-reactions into net equation
3. ✓
  Balancing $Pb + 2 Fe^{3 +} \to Pb^{2 +} + 2 Fe^{2 +}$
  1 mark · Combine half-reactions into net equation
4. Question 8.3.3 · November 2023 · Paper 2 · National (DBE) · 3 marks
A cleaned pure copper strip, Cu(s), is placed in a beaker containing a colourless silver nitrate solution, $AgNO_{3}$ (aq), at $25$ °C, as shown below.

After a while, it is observed that the solution in the beaker becomes blue.
8.3 A galvanic cell is now set up using Cu and Ag strips as electrodes. A simplified diagram of the cell is shown below.

Write down the:
8.3.3 Overall (net) balanced equation for the cell reaction(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactants $2 Ag^{+} (aq) + Cu(s)$
  1 mark · Combine half-reactions into net equation
2. ✓
  Products $\to 2 Ag(s) + Cu^{2 +} (aq)$
  1 mark · Combine half-reactions into net equation
3. ✓
  Balancing $2 Ag^{+} (aq) + Cu(s) \to 2 Ag(s) + Cu^{2 +} (aq)$
  1 mark · Combine half-reactions into net equation
5. Question 9.2.4 · May/June 2022 · Paper 2 · National (DBE) · 3 marks
The simplified diagram below represents an electrochemical cell used for the electrolysis of a concentrated sodium chloride solution, NaC $ℓ$ (aq). X and Y are carbon electrodes.
9.2 Chlorine gas, $C ℓ_{2}$ (g), is released at electrode X.

Write down the:
9.2.4 Balanced equation for the net (overall) cell reaction that takes place in the cell(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactants $2 H_{2} O (ℓ) + 2 C ℓ^{-} (aq)$
  1 mark · Combine half-reactions into net equation
2. ✓
  Products $\to C ℓ_{2} (g) + H_{2} (g) + 2 OH^{-} (aq)$
  1 mark · Combine half-reactions into net equation
3. ✓
  Balancing $2 H_{2} O (ℓ) + 2 C ℓ^{-} (aq) \to C ℓ_{2} (g) + H_{2} (g) + 2 OH^{-} (aq)$
  1 mark · Combine half-reactions into net equation
6. Question 8.2.4 · November 2022 · Paper 2 · National (DBE) · 3 marks
8.2 A standard electrochemical cell is set up as shown below.
8.2.4 Write down the balanced equation for the net cell reaction taking place.(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactants $Ni^{2 +} + Mn$
  1 mark · Combine half-reactions into net equation
2. ✓
  Products $\to Mn^{2 +} + Ni$
  1 mark · Combine half-reactions into net equation
3. ✓
  Balancing $Ni^{2 +} + Mn \to Mn^{2 +} + Ni$
  1 mark · Combine half-reactions into net equation

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