RPAL Mole Ratios 2 — Questions and Answers
Question 1: How is a mole ratio used as a conversion factor?
- It is placed as a fraction (desired moles / given moles) and multiplied by the known quantity (Correct answer)
- It is added to the known quantity of moles
- It is subtracted from the molecular weight
- It is divided by Avogadro's number
Correct answer: It is placed as a fraction (desired moles / given moles) and multiplied by the known quantity
A mole ratio serves as a conversion factor: multiply moles of known substance by (moles desired / moles given) from the balanced equation.
Question 2: For 2SO₂ + O₂ → 2SO₃, how many moles of SO₃ are produced from 3 mol SO₂?
- 3 mol SO₃ (Correct answer)
- 6 mol SO₃
- 1.5 mol SO₃
- 2 mol SO₃
Correct answer: 3 mol SO₃
The SO₂:SO₃ ratio is 2:2 (1:1), so 3 mol SO₂ produces 3 mol SO₃.
Question 3: For CH₄ + 2O₂ → CO₂ + 2H₂O, how many moles of H₂O are produced from 5 mol CH₄?
- 10 mol Hâ‚‚O (Correct answer)
- 5 mol Hâ‚‚O
- 2.5 mol Hâ‚‚O
- 15 mol Hâ‚‚O
Correct answer: 10 mol Hâ‚‚O
The CH₄:H₂O ratio is 1:2, so 5 mol CH₄ produces 5 × 2 = 10 mol H₂O.
Question 4: What is the mole ratio of O₂ to H₂O in the reaction 2H₂ + O₂ → 2H₂O?
- 1:2 (Correct answer)
- 2:1
- 1:1
- 2:2
Correct answer: 1:2
The coefficients give 1 mol Oâ‚‚ per 2 mol Hâ‚‚O, so the ratio Oâ‚‚:Hâ‚‚O = 1:2.
Question 5: In 2KClO₃ → 2KCl + 3O₂, how many moles of O₂ are produced from 4 mol KClO₃?
- 6 mol Oâ‚‚ (Correct answer)
- 4 mol Oâ‚‚
- 8 mol Oâ‚‚
- 3 mol Oâ‚‚
Correct answer: 6 mol Oâ‚‚
The KClO₃:O₂ ratio is 2:3, so 4 mol KClO₃ produces 4 × (3/2) = 6 mol O₂.
Question 6: A mole ratio can be written as either A/B or B/A. Which form do you use?
- The form that cancels the unit you want to eliminate and gives the unit you want (Correct answer)
- Always A/B regardless of context
- Always B/A regardless of context
- The form that gives the largest numerical answer
Correct answer: The form that cancels the unit you want to eliminate and gives the unit you want
Choose the form of the mole ratio that cancels the given unit and produces the desired unit in dimensional analysis.
RPAL Mole Ratios 2
How is a mole ratio used as a conversion factor?