Questions on Mole Fraction
Mole Fraction – Multiple Choice Questions
1. What is the definition of mole fraction?
A) Volume of one gas divided by the total volume
B) Mass of solute divided by mass of solvent
C) Number of moles of a component divided by total moles of the mixture
D) Partial pressure divided by total volume
E) Number of molecules per volume
2. What is the symbol for mole fraction?
A) M
B) μ
C) χ
D) φ
E) α
3. What is the formula for mole fraction of gas A in a mixture?
A) χA = nA / nT
B) χA = PA / PT
C) χA = VA / VT
D) χA = mA / mT
E) χA = TA / TT
4. What is the sum of the mole fractions of all components in a mixture?
A) 0
B) 1
C) Depends on pressure
D) Equal to Avogadro’s number
E) 100
5. Which of the following values is not possible for a mole fraction?
A) 0.00
B) 0.25
C) 1.00
D) 1.25
E) 0.50
6. In a mixture of 2 mol of A and 3 mol of B, what is the mole fraction of A?
A) 0.25
B) 0.33
C) 0.40
D) 0.50
E) 0.60
7. If the mole fraction of a gas is 0.4, what is the mole percentage?
A) 60%
B) 40%
C) 0.4%
D) 4%
E) 20%
8. What is the mole fraction of component B in a two-component system if χA = 0.65?
A) 0.25
B) 0.35
C) 0.45
D) 0.85
E) 1.65
9. Mole fraction is a dimensionless quantity because:
A) It has no units
B) It cancels volume
C) It's based on temperature
D) It depends on pressure
E) It's always zero
10. In a gas mixture with 1 mol He, 2 mol N₂, and 3 mol O₂, what is χ(N₂)?
A) 0.25
B) 0.50
C) 0.33
D) 0.20
E) 0.40
11. Which of the following is true about mole fraction?
A) It depends on temperature
B) It depends on volume
C) It’s constant for a given composition
D) It’s always less than 0.5
E) It’s measured in grams
12. Mole fraction is used in calculating:
A) Total energy
B) Vapor pressure
C) Color of a gas
D) Freezing point only
E) Boiling point elevation only
13. In a solution with 0.5 mol solute and 9.5 mol solvent, what is the mole fraction of the solute?
A) 0.005
B) 0.050
C) 0.950
D) 0.500
E) 0.090
14. If the mole fraction of water in a solution is 0.7, what is the mole fraction of solute?
A) 0.1
B) 0.2
C) 0.3
D) 0.4
E) 0.7
15. Which condition does not affect mole fraction?
A) Number of moles
B) Temperature
C) Total moles of the mixture
D) Ratio of substances
E) Type of component
16. In a binary solution, χA = 0.30. What is χB?
A) 0.30
B) 0.70
C) 1.00
D) 0.50
E) 0.10
17. Which equation connects partial pressure to mole fraction?
A) PA = VA/VT
B) PA = χA × PT
C) PA = χA / PT
D) PA = PT / χA
E) PA = χA² × PT
18. Mole fraction is most commonly used in:
A) Kinetic energy calculations
B) Stoichiometric coefficients
C) Gas mixtures and solutions
D) Ionic equations
E) Thermochemical tables
19. In a gas mixture, χCO₂ = 0.2, χN₂ = 0.3, what is χO₂?
A) 0.3
B) 0.4
C) 0.5
D) 0.6
E) 0.2
20. What is the mole fraction of a solute in a dilute solution?
A) Close to 1
B) Greater than 1
C) Close to 0
D) Exactly 0.5
E) Cannot be determined
- Questions on Ideal Gas Law
- Questions on Molar Mass of a Gas
- Questions on Dalton’s Law of Partial Pressures
Answers with Explanations
1. C – Mole fraction is moles of a component / total moles.
2. C – The Greek letter χ (chi) denotes mole fraction.
3. A – χA = nA / nT is the standard formula.
4. B – The mole fractions add up to 1 in any mixture.
5. D – Mole fraction cannot exceed 1.00.
6. C – χA = 2 / (2 + 3) = 2/5 = 0.40.
7. B – 0.4 × 100 = 40%.
8. B – If χA = 0.65, then χB = 1 - 0.65 = 0.35.
9. A – Since it’s a ratio, mole fraction has no units.
10. C – χN₂ = 2 / (1 + 2 + 3) = 2/6 = 0.33.
11. C – Mole fraction depends only on composition, not conditions.
12. B – Used in vapor pressure calculations via Raoult’s Law.
13. B – χ = 0.5 / (0.5 + 9.5) = 0.5 / 10 = 0.050.
14. C – Solute mole fraction = 1 - 0.7 = 0.3.
15. B – Temperature does not affect mole fraction directly.
16. B – In binary: χA + χB = 1 → χB = 1 - 0.3 = 0.70.
17. B – PA = χA × PT comes from Dalton’s Law.
18. C – Common in gas mixtures and solutions.
19. B – χO₂ = 1 - 0.2 - 0.3 = 0.5.
20. C – In dilute solutions, mole fraction of solute is close to 0.
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