AQA A-Level Chemistry Paper 3, 2023: Question 28

1 mark · Easy difficulty · Multiple Choice

Mole Fraction in Combustion This question assesses understanding of mole fractions in a chemical mixture, specifically calculating the mole fraction of butane (C₄H₁₀) in a mixture with oxygen (O₂) required for complete combustion based on the stoichiometry of the reaction.

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Question

AQA A-Level Chemistry Paper 3, 2023: Question 28
Question text

28 The equation for the complete combustion of butane is

C4H10 + 6 O2 → 4CO2 + 5H2O

What is the mole fraction of butane in a mixture of butane and oxygen with the

minimum amount of oxygen needed for complete combustion?

[1 mark]

A 0.133

B 0.153

C 0.167

D 0.200

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 3, 2023: Question 28

28 A 1 (AO2) 0.133

How to answer it

Mole Fraction of Butane

Question:

The equation for the complete combustion of butane is:

C4H10 + 61/2 O2 → 4 CO2 + 5 H2O

What is the mole fraction of butane in a mixture of butane and oxygen with the minimum amount of oxygen needed for complete combustion?

  • A: 0.133
  • B: 0.153
  • C: 0.167
  • D: 0.200

Correct Answer: A

The correct mole fraction of butane is 0.133 .

Explanation:

  1. The stoichiometry of the combustion reaction indicates that 1 mole of butane reacts with 6.5 moles of oxygen.
  2. The total number of moles in the mixture is:
    1 + 6.5 = 7.5 moles
  3. The mole fraction of butane is:
    (Moles of butane) / (Total moles)
    = 1 / 7.5 = 0.133

Teacher Tip: Always ensure the mole ratio is correctly determined from the balanced chemical equation. Miscalculating the ratio can lead to errors in the mole fraction.

Topics

Physical Chemistry · 3.1.2 Amount of Substance

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.