Moles, mass and molar relationships
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Moles, mass and molar relationships — Free MYP5 Chemistry Practice Questions

1QuestionMole ratios from balanced chemical equationsConcept Practice
2 marks~3 minCriterion A
The Haber process synthesises ammonia according to the following balanced equation:

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

Industrial plants use this reaction continuously, so precise mole ratios determine how much of each reactant is fed into the reactor.
a
State the mole ratio of H2H_2 to NH3NH_3 in this reaction. [1]
b
A reactor is supplied with 12 mol of H2H_2. Deduce the maximum number of moles of NH3NH_3 that can be produced, assuming N2N_2 is in excess. [1]
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Solutions

2QuestionMole ratios from balanced chemical equationsAssessment Practice
8 marks~12 minCriterion D
The Haber-Bosch process synthesises ammonia (NH3\text{NH}_3) for agricultural fertilizers:

N2(g)+3H2(g)→2NH3(g)\text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g)

For every mole of NH3\text{NH}_3 produced, approximately 0.5 mol of methane (CH4\text{CH}_4) is consumed to generate hydrogen, releasing 1.2 kg of CO2\text{CO}_2. A farmer requires 340 kg of NH3\text{NH}_3 per hectare per year for optimal crop yields. Molar mass of NH3\text{NH}_3 = 17 g mol−1^{-1}.
a
Calculate the minimum moles of H2\text{H}_2 required to produce 340 kg of NH3\text{NH}_3. [2]
b
Deduce the total CO2\text{CO}_2 emissions (in kg) from producing this quantity of NH3\text{NH}_3. [2]
c
Evaluate the societal and environmental trade-offs of using the Haber-Bosch process for fertilizer production, using your calculated data to support your conclusion. [4]
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Solutions

3QuestionInterpreting coefficients in chemical equationsConcept Practice
2 marks~3 minCriterion C
The combustion of methane is represented by the equation:

CH4+2O2→CO2+2H2OCH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

The molecular models below show the four species involved, each labelled A–D. In these models, carbon atoms are black, oxygen atoms are red, and hydrogen atoms are white.

(a) Deduce which labelled molecule represents water (H2OH_2O), and justify your answer by referring to both the molecular formula of water and the balanced equation. [2]
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Solutions

4QuestionUsing formula: moles = mass ÷ molar massConcept Practice
2 marks~3 minCriterion B
The table below shows the first five straight-chain alkanes and their molar masses.

AlkaneMethaneEthanePropaneButanePentane
Molecular formulaCH4CH_4C2H6C_2H_6C3H8C_3H_8C4H10C_4H_{10}C5H12C_5H_{12}
Molar mass (g/mol)1630445872
a
Deduce the molar mass of hexane, C6H14C_6H_{14}, without a periodic table, showing your reasoning. [1]
b
Explain why each successive alkane in this series has a molar mass exactly 14 g/mol greater than the previous one. [1]

Solutions

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