Home / iGCSE Chemistry (0620) Core:3.3 The mole and the Avogadro constant: Exam Style Questions Paper 1

iGCSE Chemistry (0620) Core:3.3 The mole and the Avogadro constant: Exam Style Questions Paper 1

iGCSE Chemistry (0620) Core Paper 1 - All Chapters
Question

The equation for the production of ammonia, NH3, is shown.

N2(g) + 3H2(g) → 2NH3(g)

Which mass of nitrogen is required to make 51 tonnes of ammonia?

A) 21 tonnes
B) 25.5 tonnes
C) 42 tonnes
D) 84 tonnes

▶️ Answer/Explanation
Solution

Ans: C

To solve this stoichiometry problem:

  1. Calculate the molar masses:
    • N2: 2 × 14 = 28 g/mol
    • NH3: 14 + (3 × 1) = 17 g/mol
  2. From the balanced equation: 1 mole N2 produces 2 moles NH3
  3. Calculate moles of NH3 in 51 tonnes:
    • 51 tonnes = 51,000,000 g
    • Moles = mass/Mr = 51,000,000/17 = 3,000,000 moles NH3
  4. Moles of N2 needed = ½ × moles NH3 = 1,500,000 moles
  5. Mass of N2 = moles × Mr = 1,500,000 × 28 = 42,000,000 g = 42 tonnes

Therefore, 42 tonnes of nitrogen are required to make 51 tonnes of ammonia.

Question

Magnesium burns in oxygen to form magnesium oxide.

The equation for the reaction is shown.

\[ 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \]

Which mass of magnesium oxide is formed when 48 g of magnesium is burned?

A) 20 g
B) 40 g
C) 80 g
D) 160 g

▶️ Answer/Explanation
Solution

Ans: C

First, calculate the moles of magnesium used:

Molar mass of Mg = 24 g/mol

Moles of Mg = 48 g ÷ 24 g/mol = 2 moles

From the equation, 2 moles of Mg produce 2 moles of MgO (1:1 ratio)

Molar mass of MgO = 24 (Mg) + 16 (O) = 40 g/mol

Mass of MgO formed = 2 moles × 40 g/mol = 80 g

Therefore, 80 g of magnesium oxide is formed when 48 g of magnesium is burned.

Question

Calcium carbonate, CaCO3, reacts with dilute hydrochloric acid to produce carbon dioxide. The equation for the reaction is shown. The relative formula mass of calcium carbonate is 100.
                                      \(CaCO_{3}+2HCl \rightarrow CaCl_{2}+H_{2}O+CO_{2}\)
10 g of calcium carbonate is reacted with an excess of dilute hydrochloric acid. Which mass of carbon dioxide is produced?
A. 2.2 g               B. 2.8 g                    C. 4.4 g                       D. 44 g

▶️Answer/Explanation

Ans:

C

1o g CaCO3, has \(\frac{10 g}{100 g}\) = 0.1 mol 

\(CaCO_{3}+2HCl \rightarrow CaCl_{2}+H_{2}O+CO_{2}\) 

1 mol CaCO3 gives 1 mol CO2,

0.1 mol CaCO3 gives 0.1 mol CO2,

Mass of CO2, produced = 0.1*44 = 4.4 g.

Question

 The equation for the reaction between magnesium and dilute sulfuric acid is shown.

\(Mg + H_2SO_4 → MgSO_4 + H_2\)

Mr of \(MgSO_4\) is 120

Which mass of magnesium sulfate will be formed if 12 g of magnesium are reacted with sulfuric acid?

A 5g           B 10g           C 60g            D 120g

▶️Answer/Explanation

Ans: C

\(Mg + H_2SO_4 → MgSO_4 + H_2\)

1 mol Mg forms 1 mol \(MgSO_4\) 

12 g of magnesium has \(\frac{12 g}{24 g}\) = 0.5 mol Mg 

0.5 mol Mg will form 0.5 mol \(MgSO_4\)  

Mr of \(MgSO_4\) is 120 

0.5 mol \(MgSO_4\)  will have mass of 0.5*120 = 60 g. 

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