Grade 12 Physical Sciences · Paper 2 (Chemistry)

Chemical Change Grade 12

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Question 9.1 · May/June 2025 · Paper 2 · National (DBE) · 2 marks

The simplified diagram below represents an electrolytic cell used to demonstrate the electrolysis of a concentrated sodium chloride solution, NaCℓ(aq).

X and Y are carbon electrodes. Diagram for this question

9.1 Define the term electrolysis.(2)

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

What's in Chemical Change Grade 12

Each skill is one thing a memo gives a tick for. Tap a skill for its own questions, notes and videos.

Reaction Rate84 past paper questions

Chemical Equilibrium83 past paper questions

Acids and Bases76 past paper questions

Electrochemical Reactions103 past paper questions

More Chemical Change Grade 12 questions and answers

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1. Question 1.5 · November 2025 · Paper 2 · National (DBE) · 2 marks
Various options are provided as possible answers to the following questions. Each question has only ONE correct answer.
1.5 The following reaction reaches equilibrium in a closed container:

$H_{2} (g) + S(s) ⇌ H_{2} S(g)$ $Δ H < 0$

The reaction rate versus time graph for the reaction is given below.

What change was made to the system at time $t_{1}$ ?(2)
1. A The pressure was increased at a constant temperature.
2. B The volume of the container was increased.
3. C The temperature was increased.
4. D More hydrogen was added to the system.
Show the memo (1 tick)Memo
1. ✓
  Correct optionAt $t_{1}$ both rates jump up suddenly by the same amount and stay equal, so the equilibrium position does not shift. There is 1 mol of gas on each side, so increasing the pressure raises both rates equally. Increasing the temperature would favour the endothermic reverse reaction, so the reverse rate would rise more. Adding $H_{2}$ would only make the forward rate jump. Increasing the volume would lower the rates.
  
  Answer: A
  2 marks · Interpret equilibrium graphs
2. Question 8.3 · May/June 2024 · Paper 2 · National (DBE) · 2 marks
The relationship between the concentration of the electrolyte and the cell potential is investigated using the following electrochemical cell represented by the cell notation:

Aℓ(s) | $A ℓ^{3 +}$ (aq) || $M^{2 +}$ (aq) | M(s)

The concentration of $M^{2 +}$ is changed and the corresponding emf is measured. The concentration of $A ℓ^{3 +}$ (aq) and the temperature are at standard conditions. The graph below shows the results of this investigation.
8.3 How will the concentration of $M^{2 +}$ (aq) be affected as the cell operates? Choose from INCREASES, DECREASES or REMAINS THE SAME.

Give a reason for the answer.(2)
Show the memo (2 ticks)Memo
1. ✓
  Effect on [M $^{2 +}$ ]Decreases
  1 mark · Describe a galvanic cell
2. ✓
  Reason $M^{2 +}$ is reduced / $M^{2 +}$ used up / $M^{2 +}$ is the oxidising agent.
  1 mark · Describe a galvanic cell
3. Question 7.1.1 · May/June 2024 · Paper 2 · National (DBE) · 3 marks
7.1 A standard solution is prepared by dissolving 10 g of sodium carbonate, $Na_{2} CO_{3}$ (s), in $0, 7$ dm $^{3}$ of water.

Answer the questions that follow.
7.1.1 Calculate the concentration of the solution.(3)
Show the memo (3 ticks)Memo
1. ✓
  Formula $c = \frac{m}{M V}$
  1 mark · Calculate concentration of a solution
2. ✓
  Substitution $c = \frac{10}{( 106 ) ( 0 , 7 )}$
  1 mark · Calculate concentration of a solution
3. ✓
  Answer with unit $c = 0, 13$ mol·dm $^{- 3}$
  1 mark · Calculate concentration of a solution
4. Question 4.2.1 · November 2025 · Paper 1 · National (DBE) · 3 marks
Cricketers at an academy conduct an experiment to determine the relationship between the contact time and the final momentum of a ball for a constant average net force.

A cricket ball of mass $150$ g is thrown horizontally with a certain initial velocity and is struck by a bat so that the ball moves in the opposite direction, as shown in the diagram below. The average net force acting on the ball is horizontal.

The experiment is repeated using the same ball. The average net force and the initial velocity of the ball are kept constant. The contact time between the bat and the ball is changed EACH time. The results obtained are shown in the sketch graph below.
4.2 Calculate the:
4.2.1 Average net force acting on the ball(3)
Show the memo (3 ticks)Memo
1. ✓
  METHOD 1: Change in final momentum (numerator)Gradient $= F_{n e t} = \frac{Δ p _{f}}{Δ ( Δ t )}$
  $= \frac{4 , 5 - 0}{\dots}$
  1 mark · Read a graph of results
2. ✓
  METHOD 1: Change in contact time (denominator) $F_{n e t} = \frac{4 , 5 - 0}{0 , 03 - 0 , 01} = 225$ N
  1 mark · Read a graph of results
3. ✓
  METHOD 1: Answer with direction $F_{n e t} = 225$ N to the right / opposite to the original direction of the ball
  1 mark · Read a graph of results
5. Question 1.5 · November 2024 · Paper 2 · National (DBE) · 2 marks
Various 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) next to the question numbers (1.1 to 1.10) in the ANSWER BOOK, e.g. 1.11 E.
1.5 Initially, an equal number of moles of hydrogen gas, $H_{2}$ (g), and iodine gas, $I_{2}$ (g), are mixed in a closed container. The reaction reaches equilibrium at a constant temperature according to the balanced equation.

$H_{2} (g) + I_{2} (g) ⇌ 2 HI(g)$

Which ONE of the following is ALWAYS TRUE at equilibrium?(2)
1. A $[H_{2}] = [I_{2}]$
2. B $[HI] = [I_{2}]$
3. C $[HI] = 2 [H_{2}]$
4. D $[H_{2}] = [I_{2}] = [HI]$
Show the memo (1 tick)Memo
1. ✓
  Correct option $H_{2}$ and $I_{2}$ start with equal amounts and react in a $1 : 1$ ratio, so the same amount $x$ of each is used. At equilibrium both are $n - x$ : $[H_{2}] = [I_{2}]$ always.
  How much HI forms depends on $K_{c}$ , so B, C and D are true only for particular values of $K_{c}$ .
  
  Answer: A
  2 marks · Complete an equilibrium table

Chemical Change Grade 12 videos

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

Energy and Chemical Change grade 11: Activation energy, heat of reaction, catalyst and MORE!Miss Martins Maths and Science

Energy and chemical change Heat Of Reaction Grade 11 & 12 ChemistryMiss Martins Maths and Science

Collision Theory grade 12: Part 1Kevinmathscience

Rate and extent of reaction: HOW TO CALCULATE the rate of reaction Grade 12 ChemistryMiss Martins Maths and Science

Rate of Reaction Graphs Grade 12 ChemistryMiss Martins Maths and Science

Maxwell Boltzmann Distribution Curve grade 12Kevinmathscience

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