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

Stoichiometry Grade 11

Real Stoichiometry past paper questions and answers from 2022 to 2025, 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 1.3 · May/June 2025 · Paper 2 · National (DBE) · 2 marks

1.3 A compound

CH_{3} (CH_{2})_{5} CH_{3}

undergoes the following reaction:

CH_{3} (CH_{2})_{5} CH_{3} \to R + CH_{3} (CH_{2})_{2} CH_{3}

Which ONE of the following combinations CORRECTLY describes the type of reaction and the IUPAC name of compound R?(2)

A Type: Elimination; IUPAC name: Propane
B Type: Addition; IUPAC name: Propene
C Type: Cracking; IUPAC name: Propane
D Type: Cracking; IUPAC name: Propene

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More Stoichiometry Grade 11 questions and answers

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4. Question 2.3.2 · November 2025 · Paper 2 · National (DBE) · 5 marks
The letters A to G in the table below represent organic compounds.
2.3 Compound E, $C_{3} H_{8}$ (g), reacts with oxygen, $O_{2}$ (g), according to the balanced equation:

$C_{3} H_{8} (g) + 5 O_{2} (g) \to 3 CO_{2} (g) + 4 H_{2} O(g)$

Initially $8$ cm $^{3}$ of compound E and $50$ cm $^{3}$ of oxygen were injected into a container of adjustable volume and allowed to react, as shown below.

Answer the questions that follow.
2.3.2 Calculate the TOTAL volume of the GASES present in the container at the end of the reaction.(5)
Show the memo (5 ticks)Memo
1. ✓
  (a) Volume of O2 used (with volume of C3H8) $V (O_{2})_{used} = 5 V (C_{3} H_{8}) = (5) (8) = 40$ cm $^{3}$
  1 mark · Use the mole ratio
2. ✓
  (b) Volumes of CO2 and H2O produced $V (CO_{2})_{formed} = 3 V (C_{3} H_{8}) = (3) (8) = 24$ cm $^{3}$
  $V (H_{2} O)_{formed} = 4 V (C_{3} H_{8}) = (4) (8) = 32$ cm $^{3}$
  1 mark · Use the mole ratio
3. ✓
  (c) Volume of O2 remaining $V (O_{2})_{unused} = 50 - 40 = 10$ cm $^{3}$
  1 mark · Identify the limiting reagent
4. ✓
  (d) Addition of the three volumesVolume of gas in the container $= 10 + 24 + 32$
  1 mark · Identify the limiting reagent
5. ✓
  (e) Final answerTotal volume of gas in the container $= 66$ cm $^{3}$ (or $0, 066$ dm $^{3}$ )
  1 mark · Identify the limiting reagent
5. Question 1.4 · November 2023 · 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).
1.4 Hydrochloric acid reacts with EXCESS zinc:

$Zn(s) + 2 HCl(aq) \to ZnCl_{2} (aq) + H_{2} (g)$

Different reaction conditions are shown in the diagrams below. The mass of zinc used is the same in both test tubes.

How will the INITIAL rate of reaction and FINAL VOLUME of $H_{2}$ (g) produced in test tube Y compare with that in test tube X?(2)
1. A Initial rate of reaction in Y: Higher; Final volume of $H_{2}$ (g) in Y: Equal
2. B Initial rate of reaction in Y: Lower; Final volume of $H_{2}$ (g) in Y: More
3. C Initial rate of reaction in Y: Lower; Final volume of $H_{2}$ (g) in Y: Equal
4. D Initial rate of reaction in Y: Higher; Final volume of $H_{2}$ (g) in Y: More
Show the memo (1 tick)Memo
1. ✓
  Correct optionRate: both tubes have the same acid concentration ( $0, 1$ mol·dm $^{- 3}$ ), but Y has zinc LUMPS (smaller surface area), so the initial rate in Y is LOWER.
  Final volume: zinc is in excess, so HCl is the limiting reactant.
  X: $n (HCl) = (0, 1) (0, 1) = 0, 01$ mol. Y: $n (HCl) = (0, 1) (0, 2) = 0, 02$ mol.
  Y has more HCl, so it produces MORE $H_{2}$ .
  
  Answer: B
  2 marks · Identify the limiting reagent
6. Question 4.1.2 · November 2023 · Paper 2 · National (DBE) · 3 marks
4.1 Consider the cracking reaction below.

$C_{16} H_{34} \to C_{6} H_{14} + C_{6} H_{x} + 2 C_{y} H_{z}$
4.1.2 Write down the values represented by x, y and z in the equation above.(3)
Show the memo (3 ticks)Memo
1. ✓
  Value of x $x = 12$
  1 mark · Use conservation of mass
2. ✓
  Value of y $y = 2$
  1 mark · Use conservation of mass
3. ✓
  Value of z $z = 4$
  1 mark · Use conservation of mass
7. Question 2.4 · May/June 2023 · Paper 2 · National (DBE) · 6 marks
Study the table below and answer the questions that follow.
2.4 A $2$ g sample of compound E contains $1, 09$ g carbon and $0, 18$ g hydrogen. The molecular mass of compound E is $88$ g·mol $^{- 1}$ .

Determine the molecular formula of compound E by means of a calculation.(6)
Show the memo (5 ticks)Memo
1. ✓
  Calculate the mass of oxygen $m (O) = 2 - (1, 09 + 0, 18) = 0, 73$ g
  1 mark · Determine empirical and molecular formulae
2. ✓
  Substitute mass and molar mass for C and H into n = m/M $n (C) = \frac{1 , 09}{12} = 0, 0908$ mol
  $n (H) = \frac{0 , 18}{1} = 0, 18$ mol
  1 mark · Determine empirical and molecular formulae
3. ✓
  Substitute mass and molar mass for O into n = m/M $n (O) = \frac{0 , 73}{16} = 0, 046$ mol
  1 mark · Determine empirical and molecular formulae
4. ✓
  Simplify ratioC : H : O = $0, 0908 : 0, 18 : 0, 046$ = $2 : 4 : 1$
  Empirical formula: $C_{2} H_{4} O$
  1 mark · Determine empirical and molecular formulae
5. ✓
  Correct molecular formula $M (C_{2} H_{4} O) \times n = 88$
  $44 n = 88$
  $n = 2$
  Molecular formula: $C_{4} H_{8} O_{2}$
  2 marks · Determine empirical and molecular formulae
8. Question 5.2 · May/June 2023 · Paper 2 · National (DBE) · 2 marks
Consider the following decomposition reaction that takes place in a sealed $2$ dm $^{3}$ container:

$2 N_{2} O_{5} (g) \to 4 NO_{2} (g) + O_{2} (g)$

The graph below shows how the concentrations of $N_{2} O_{5}$ (g) and $NO_{2}$ (g) change with time.
5.2 Consider the statement below:

The rate of decomposition of $N_{2} O_{5}$ (g) is half the rate of formation of $NO_{2}$ (g).

Is this statement TRUE or FALSE? Give a reason for the answer.(2)
Show the memo (2 ticks)Memo
1. ✓
  True or falseTrue
  1 mark · Use the mole ratio
2. ✓
  Reasonn mol of $N_{2} O_{5}$ forms 2n mol of $NO_{2}$ per unit time.
  1 mark · Use the mole ratio
9. Question 5.3.2 · November 2022 · Paper 2 · National (DBE) · 4 marks
Three experiments, A, B and C, are carried out to investigate some of the factors that affect the rate of decomposition of hydrogen peroxide, $H_{2} O_{2} (ℓ)$ .

The balanced equation for the reaction is:

$2 H_{2} O_{2} (ℓ) \to 2 H_{2} O (ℓ) + O_{2} (g)$

Identical samples of hydrogen peroxide are used in each experiment.

The conditions used in each experiment are summarised in the table below.
5.3 The volume of oxygen gas, $O_{2}$ (g), produced in experiment B during the first $3, 6$ s is collected in a syringe, as shown below.
5.3.2 Calculate the mass of water, $H_{2} O (ℓ)$ , that was produced during the first $3, 6$ s. Take the molar gas volume to be $24000$ cm $^{3}$ ·mol $^{- 1}$ at $25$ °C.(4)
Show the memo (4 ticks)Memo
1. ✓
  Substitute into n = V/Vm $n (O_{2}) = \frac{V}{V _{m}} = \frac{560}{24 000} = 0, 023$ mol $(0, 0233)$
  1 mark · Calculate number of moles
2. ✓
  Mole ratio $n (H_{2} O) = 2 n (O_{2}) = 2 (0, 023) = 0, 046$ mol $(0, 0467)$
  1 mark · Use the mole ratio
3. ✓
  Substitute into m = nM $m = n M = 0, 046 \times 18$
  1 mark · Calculate number of moles
4. ✓
  Final answer $m = 0, 83$ g
  1 mark · Calculate number of moles
10. Question 4.2.4 · May/June 2022 · Paper 2 · National (DBE) · 3 marks
4.2 The cracking of a long chain hydrocarbon, $C_{10} H_{22}$ , takes place in test tube A, as shown below.

Two STRAIGHT CHAIN organic compounds, X and Z, are produced in test tube A according to the following balanced equation:

$C_{10} H_{22} (ℓ) \to 2 X (g) + Z (g)$

Answer the questions that follow.
4.2.4 Write down the molecular formula of compound Z.(3)
Show the memo (1 tick)Memo
1. ✓
  Molecular formula of Z $C_{2} H_{6}$
  
  OR $C_{4} H_{10}$ OR $C_{6} H_{14}$
  3 marks · Use conservation of mass

Stoichiometry Grade 11 videos

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

Conservation Of Mass Grade 10Kevinmathscience

Stoichiometry: Mole Ratios | Grade 10, 11 and 12 ChemistryMiss Martins Maths and Science

The mole concept: What is a mole? Quantitative aspects of chemical changeMiss Martins Maths and Science

How to calculate moles using mass | Stoichiometry grade 10, 11 and 12Miss Martins Maths and Science

Concentration of solutions ChemistryMiss Martins Maths and Science

Empirical Formula: How to calculate | Stoichiometry | ChemistryMiss Martins Maths and Science

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