Grade 10 Physical Sciences · Chemical Change · Paper 2 (Chemistry)

Stoichiometry Grade 10

Real Stoichiometry past paper questions and answers from 2018 to 2024, 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 1.4 · 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) in the ANSWER BOOK, e.g. 1.11 E. Each question has only ONE correct answer.

1.4 Avogadro's number is equal to the number of ...(2)

A atoms in 1 mole CO.
B atoms in 1 mole $Br_{2}$ .
C molecules in 1 mole Au.
D molecules in 1 mole $N_{2}$ .

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More Stoichiometry Grade 10 questions and answers

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4. Question 5.6.1 · November 2018 · Paper 2 · National (DBE) · 2 marks
Study the physical and chemical processes below and answer the questions that follow.

X: $H_{2} O(s) \to H_{2} O(g)$

Y: $CaCO_{3} (s) Δ CaO(s) + CO_{2} (g)$

Z: Iron + Oxygen $\to$ Iron(III) oxide
5.6 A $20$ g sample of $CaCO_{3}$ (s) in process Y decomposes to form $11, 2$ g of CaO. In a second sample, $30$ g decomposes to form $x$ g of $CO_{2}$ .

Answer the questions that follow.
5.6.1 State the law of constant composition.(2)
Show the memo (1 tick)Memo
1. ✓
  Law of constant compositionNo matter how a chemical compound is prepared, it always contains the same elements in the same proportion by mass.
  2 marks · Define stoichiometry terms and laws
5. Question 1.5 · November 2024 · Paper 2 · Provincial · 2 marks
1.5 What is the percentage of hydrogen in a molecule of hydrogen peroxide with molar mass of $34$ g·mol $^{- 1}$ , if one mole of hydrogen reacts with one mole of oxygen?(2)
1. A $72, 72$ %
2. B $94, 12$ %
3. C $11, 11$ %
4. D $5, 88$ %
Show the memo (1 tick)Memo
1. ✓
  Correct optionHydrogen peroxide is $H_{2} O_{2}$ : one mole of $H_{2}$ ( $2$ g) with one mole of $O_{2}$ ( $32$ g).
  % H $= \frac{2}{34} \times 100 = 5, 88$ %
  
  Answer: D
  2 marks · Determine empirical and molecular formulae
6. Question 7.1 · November 2024 · Paper 2 · Provincial · 4 marks
7.1 Calculate the concentration of a solution prepared by dissolving $5, 85$ g of sodium chloride in enough water to make a $500$ cm $^{3}$ solution.(4)
Show the memo (4 ticks)Memo
1. ✓
  OPTION 1: Moles of NaCl $n (NaC ℓ) = \frac{m}{M} = \frac{5 , 85}{58 , 5}$
  $= 0, 1$ mol
  1 mark · Calculate number of moles
2. ✓
  OPTION 1: Formula $c (NaC ℓ) = \frac{n}{V}$
  1 mark · Calculate concentration of a solution
3. ✓
  OPTION 1: Substitution $= \frac{0 , 1}{0 , 5}$
  1 mark · Calculate concentration of a solution
4. ✓
  OPTION 1: Answer with unit $= 0, 2$ mol·dm $^{- 3}$
  1 mark · Calculate concentration of a solution
7. Question 1.4 · November 2024 · Paper 2 · Provincial · 2 marks
1.4 The molar mass of hydrated oxalic acid $(COOH)_{2} \cdot x H_{2} O$ is $126$ g·mol $^{- 1}$ .

The number of water molecules ( $x$ ) present in the hydrated compound is ...(2)
1. A 1.
2. B 2.
3. C 3.
4. D 4.
Show the memo (1 tick)Memo
1. ✓
  Work back from the molar mass to x $M ((COOH)_{2}) = 2 (12 + 16 + 16 + 1) = 90$ g·mol $^{- 1}$
  Mass of water: $126 - 90 = 36$ g·mol $^{- 1}$
  $x = \frac{36}{18} = 2$
  
  Answer: B
  2 marks · Calculate molar mass
8. Question 1.5 · June 2024 · Paper 2 · Provincial · 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 1.5) in the ANSWER BOOK, e.g. 1.6 C.
1.5 Which ONE of the following represents 1 mole of a substance?(2)
1. A $16$ g oxygen gas
2. B $2$ g hydrogen gas
3. C $22, 4$ dm $^{3}$ copper
4. D $22, 4$ cm $^{3}$ nitrogen gas
Show the memo (1 tick)Memo
1. ✓
  Correct optionHydrogen gas is $H_{2}$ , so $M = 2$ g·mol $^{- 1}$ and $n = \frac{m}{M} = \frac{2}{2} = 1$ mol.
  A: oxygen gas is $O_{2}$ ( $M = 32$ g·mol $^{- 1}$ ), so $16$ g is $0, 5$ mol.
  C: $22, 4$ dm $^{3}$ is the molar volume of a GAS at STP; copper is a solid.
  D: the volume is in cm $^{3}$ , not dm $^{3}$ .
  
  Answer: B
  2 marks · Calculate number of moles
9. Question 5.1 · June 2024 · Paper 2 · Provincial · 2 marks
The reaction of sodium carbonate and hydrochloric acid produces table salt, water and carbon dioxide according to the following balanced chemical equation.

$Na_{2} CO_{3} + 2 HC ℓ \to 2 NaC ℓ + H_{2} O + CO_{2}$
5.1 Define the term mole of a substance.(2)
Show the memo (1 tick)Memo
1. ✓
  Definition of a moleA mole of a substance is the same amount of particles as there is atoms in 12 g of the Carbon-12 isotope.
  2 marks · Define stoichiometry terms and laws
10. Question 1.7 · November 2023 · 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) next to the question numbers (1.1 to 1.9) in the ANSWER BOOK, e.g. 1.10 D.
1.7 The percentage water in $MgSO_{4} \cdot 7 H_{2} O$ is:(2)
1. A $51, 22$
2. B $48, 78$
3. C $21$
4. D $7$
Show the memo (1 tick)Memo
1. ✓
  Correct option $M (MgSO_{4} \cdot 7 H_{2} O) = 24 + 32 + 4 (16) + 7 (18) = 246$ g·mol $^{- 1}$
  Mass of water $= 7 \times 18 = 126$ g
  % water $= \frac{126}{246} \times 100 = 51, 22%$
  
  Answer: A
  2 marks · Determine empirical and molecular formulae

Stoichiometry Grade 10 videos

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

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 Molar MassMiss 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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