The Mole Concept and Avogaro's constant
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The Mole Concept and Avogaro's constant — Free MYP5 Chemistry Practice Questions

1QuestionConverting between moles and number of particles (atoms, molecules, ions)Concept Practice
2 marks~3 minCriterion A
Hydrogen gas reacts with oxygen gas to produce water vapour in a combustion reaction studied in industrial fuel-cell technology.
a
Construct the balanced chemical equation for this reaction, including state symbols. [1]
b
Explain how Avogadro's constant connects the number of water molecules produced to the amount of water in moles. [1]
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Solutions

2QuestionRelationship between molar mass and one mole of substanceAssessment Practice
4 marks~6 minCriterion C
A laboratory balance shows two separate samples: one pile of 1 mole of carbon atoms (molar mass 12.01 g mol−112.01 \text{ g mol}^{-1}) and one pile of 1 mole of magnesium atoms (molar mass 24.31 g mol−124.31 \text{ g mol}^{-1}).
a
State the number of atoms present in each pile and identify the constant this number represents. [1]
b
Explain why the two piles contain equal numbers of atoms despite having different masses. [2]
c
A student claims: "Because magnesium atoms are heavier, 1 mole of magnesium must contain more atoms than 1 mole of carbon." Evaluate this claim. [1]
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Solutions

3QuestionDefinition of a mole and amount of substanceConcept Practice
3 marks~5 minCriterion B
The table below shows data for one mole of four substances.

Substance — Mass of one mole (g) — Number of particles

Carbon (C) — 12.0 — 6.02×10236.02 \times 10^{23}

Water (H2_2O) — 18.0 — 6.02×10236.02 \times 10^{23}

Sodium chloride (NaCl) — 58.5 — 6.02×10236.02 \times 10^{23}

Oxygen (O2_2) — 32.0 — 6.02×10236.02 \times 10^{23}
a
State what the data shows about the number of particles present in one mole of each substance. [1]
b
Identify the pattern in molar mass shown by the four substances. [1]
c
Explain what the relationship between molar mass and number of particles reveals about the definition of a mole. [1]

Solutions

4QuestionRelationship between molar mass and one mole of substanceAssessment Practice
8 marks~12 minCriterion D
The Haber-Bosch process produces ammonia (NH3) for fertilisers:

N2+3H2→2NH3N_2 + 3H_2 \rightarrow 2NH_3

Molar masses: N2 = 28 g/mol, H2 = 2 g/mol, NH3 = 17 g/mol.

Global ammonia production relies on hydrogen derived from natural gas, generating approximately 1.9 tonnes of CO2 per tonne of NH3 produced.
a
Calculate the total mass of reactants needed to produce 34 g of NH3, and calculate the mass efficiency, defined as:

mass efficiency=mass of productmass of reactants×100%\text{mass efficiency} = \frac{\text{mass of product}}{\text{mass of reactants}} \times 100\% [2]
b
Evaluate the societal benefits of the Haber-Bosch process against its environmental costs, using the CO2 emission data provided. [3]
c
Discuss the limitations of using molar mass and mass efficiency as the sole indicators of the sustainability of the Haber-Bosch process, identifying additional factors that should be considered. [3]
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Solutions

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