Questions about Mole Ratios
Mole Ratios – Multiple-Choice Questions
1. What is a mole ratio in chemistry?
A) A comparison of grams of substances
B) A ratio of moles between two elements in the periodic table
C) A ratio of moles between any two substances in a balanced chemical equation
D) The atomic mass ratio of isotopes
E) A comparison of temperature and pressure
2. In the reaction 2H₂ + O₂ → 2H₂O, what is the mole ratio of H₂ to O₂?
A) 1:1
B) 1:2
C) 2:1
D) 2:2
E) 1:3
3. In the equation 2Al + 3Cl₂ → 2AlCl₃, what is the mole ratio of Al to AlCl₃?
A) 2:1
B) 1:2
C) 2:3
D) 3:2
E) 1:1
4. From the equation 4Fe + 3O₂ → 2Fe₂O₃, the mole ratio of Fe to O₂ is:
A) 2:3
B) 4:3
C) 3:4
D) 1:1
E) 1:2
5. What is the mole ratio of reactants in the equation N₂ + 3H₂ → 2NH₃?
A) 3:1
B) 1:3
C) 1:2
D) 2:3
E) 2:1
6. In a balanced chemical equation, the coefficients represent:
A) Masses of the substances
B) Charges of the ions
C) Number of molecules
D) Mole ratios
E) Volumes of solids
7. Which mole ratio comes from this reaction: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O?
A) O₂ to CO₂ = 5:3
B) H₂O to CO₂ = 3:4
C) C₃H₈ to O₂ = 3:5
D) CO₂ to H₂O = 4:3
E) O₂ to C₃H₈ = 1:5
8. Which ratio shows the number of moles of CO₂ produced per mole of C₄H₁₀ burned in C₄H₁₀ + 13/2O₂ → 4CO₂ + 5H₂O?
A) 1:1
B) 1:2
C) 1:4
D) 1:5
E) 4:1
9. In the reaction 2Na + Cl₂ → 2NaCl, the mole ratio of Na to NaCl is:
A) 2:1
B) 1:2
C) 1:1
D) 2:2
E) 1:3
10. What is the mole ratio of O₂ to CO₂ in this reaction: CH₄ + 2O₂ → CO₂ + 2H₂O?
A) 1:1
B) 2:1
C) 1:2
D) 2:2
E) 1:3
11. In the reaction 2KClO₃ → 2KCl + 3O₂, the mole ratio of KClO₃ to O₂ is:
A) 2:2
B) 3:2
C) 2:3
D) 1:1
E) 3:3
12. Mole ratios are used to convert between:
A) Molecules and atoms
B) Moles of one substance to moles of another
C) Mass and volume
D) Grams and liters
E) Temperature and volume
13. In a balanced equation, a 1:3 mole ratio means:
A) One mole of the product reacts with three moles of solvent
B) One mole of a substance reacts with three moles of another
C) Three grams react with one gram
D) The compound contains 3 atoms
E) Three molecules are in one mole
14. Which expression is an example of a correct mole ratio?
A) 2 mol H₂/3 mol O₂
B) 2 g H₂/3 mol O₂
C) 3 mol O₂/2 g H₂
D) 2 mol H₂O/1 atm
E) 2 mol H/1 mol O
15. From the reaction: 2H₂ + O₂ → 2H₂O, how many moles of water are made from 5 moles of O₂?
A) 5
B) 10
C) 2.5
D) 1
E) 7
16. In the reaction: 2Mg + O₂ → 2MgO, what is the mole ratio of Mg to MgO?
A) 1:2
B) 2:1
C) 2:2
D) 1:1
E) 1:3
17. Which is NOT a valid mole ratio from the reaction: 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O?
A) 2 mol C₂H₆ / 7 mol O₂
B) 4 mol CO₂ / 6 mol H₂O
C) 2 mol C₂H₆ / 4 mol CO₂
D) 7 mol O₂ / 6 mol H₂O
E) 6 mol O₂ / 4 mol CO₂
18. If 6 moles of Cl₂ react with 2Al, what is the mole ratio of Cl₂ to Al in the reaction 2Al + 3Cl₂ → 2AlCl₃?
A) 3:2
B) 2:3
C) 6:2
D) 1:1
E) 2:6
19. In the equation: 2H₂O → 2H₂ + O₂, the mole ratio of H₂ to O₂ is:
A) 1:1
B) 2:2
C) 2:1
D) 1:2
E) 3:2
20. What is the purpose of using mole ratios in chemistry?
A) To identify physical states of substances
B) To balance charges in a compound
C) To convert between different chemicals in a reaction
D) To calculate temperature
E) To determine the density of gases
Answers with Explanations
1. C – Mole ratios are from balanced chemical equations and relate two substances.
2. C – Coefficients show H₂:O₂ is 2:1.
3. E – 2 mol Al makes 2 mol AlCl₃ → ratio = 1:1.
4. B – Fe:O₂ = 4:3 in the balanced reaction.
5. B – N₂:H₂ = 1:3 in the equation.
6. D – Coefficients give the mole ratios.
7. A – 5 mol O₂ → 3 mol CO₂ = 5:3.
8. C – 1 mol C₄H₁₀ → 4 mol CO₂ = 1:4.
9. C – 2 mol Na → 2 mol NaCl = 1:1.
10. B – 2 mol O₂ → 1 mol CO₂ = 2:1.
11. C – 2 mol KClO₃ → 3 mol O₂ = 2:3.
12. B – This is the primary function of mole ratios.
13. B – This is the correct interpretation.
14. A – This is a valid mole-to-mole comparison.
15. B – 1 mol O₂ → 2 mol H₂O, so 5 mol → 10 mol H₂O.
16. D – Mg:MgO = 2:2 = 1:1.
17. E – 6 mol O₂ is not part of the balanced equation; the rest are valid.
18. A – The original reaction has Cl₂:Al = 3:2, which matches.
19. C – 2 mol H₂ and 1 mol O₂ = 2:1.
20. C – Mole ratios allow conversions between reactants and products.
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