Questions on Molar Mass: Practice Problems and Answer Key

Questions on Molar Mass

Molar mass is one of the most important quantitative concepts in chemistry because it provides the foundation for stoichiometry, chemical equations, and molecular analysis. Developed by a Science Teacher and Education Specialist, this collection of questions combines academic expertise with practical classroom applications. Designed for teachers, homeschool educators, and students preparing for chemistry examinations, these exercises help strengthen problem-solving skills and deepen understanding of matter at the molecular level.

What is Molar mass? The mass of one mole of a substance and is typically expressed in grams per mole (g/mol). It is determined by adding the atomic masses of all the atoms present in a chemical formula. Understanding molar mass is essential for converting between mass, moles, and the number of particles, making it a fundamental concept in stoichiometry and quantitative chemistry.

Multiple-Choice Questions: Molar Mass

1. What is the molar mass of water (H₂O)?

A) 10.0 g/mol

B) 16.0 g/mol

C) 18.0 g/mol

D) 20.0 g/mol

E) 12.0 g/mol

2. Which compound has a molar mass closest to 44.0 g/mol?

A) CH₄

B) CO₂

C) H₂O

D) NH₃

E) O₂

3. What is the molar mass of NaCl? (Na = 23, Cl = 35.5)

A) 58.5 g/mol

B) 60.0 g/mol

C) 55.0 g/mol

D) 50.5 g/mol

E) 57.0 g/mol

4. What is the molar mass of glucose (C₆H₁₂O₆)?

A) 160 g/mol

B) 180 g/mol

C) 200 g/mol

D) 210 g/mol

E) 120 g/mol

5. Which of the following has the lowest molar mass?

A) CO₂

B) CH₄

C) NH₃

D) H₂O

E) H₂

6. What is the molar mass of sulfuric acid (H₂SO₄)?

A) 94 g/mol

B) 96 g/mol

C) 98 g/mol

D) 100 g/mol

E) 102 g/mol

7. What is the molar mass of calcium carbonate (CaCO₃)? (Ca = 40, C = 12, O = 16)

A) 100 g/mol

B) 92 g/mol

C) 88 g/mol

D) 106 g/mol

E) 98 g/mol

8. Which compound has a molar mass of approximately 34 g/mol?

A) H₂O₂

B) NH₃

C) H₂S

D) CH₄

E) O₂

9. What is the molar mass of methane (CH₄)?

A) 12 g/mol

B) 14 g/mol

C) 16 g/mol

D) 18 g/mol

E) 20 g/mol

10. What is the molar mass of aluminum sulfate, Al₂(SO₄)₃? (Al = 27, S = 32, O = 16)

A) 294 g/mol

B) 314 g/mol

C) 342 g/mol

D) 366 g/mol

E) 278 g/mol

11. What is the molar mass of ethanol (C₂H₅OH)?

A) 42 g/mol

B) 46 g/mol

C) 50 g/mol

D) 52 g/mol

E) 48 g/mol

12. Which compound has a molar mass of about 28 g/mol?

A) CO

B) N₂

C) NO

D) O₂

E) All of the above

13. What is the molar mass of nitrogen gas (N₂)?

A) 14.0 g/mol

B) 15.0 g/mol

C) 16.0 g/mol

D) 28.0 g/mol

E) 30.0 g/mol

14. What is the molar mass of potassium hydroxide (KOH)? (K = 39, O = 16, H = 1)

A) 54 g/mol

B) 56 g/mol

C) 57 g/mol

D) 59 g/mol

E) 60 g/mol

15. What is the molar mass of magnesium nitrate, Mg(NO₃)₂? (Mg = 24, N = 14, O = 16)

A) 112 g/mol

B) 128 g/mol

C) 148 g/mol

D) 96 g/mol

E) 116 g/mol

16. What is the molar mass of acetic acid (CH₃COOH)?

A) 60 g/mol

B) 62 g/mol

C) 64 g/mol

D) 58 g/mol

E) 66 g/mol

17. Which of the following compounds has the highest molar mass?

A) H₂SO₄

B) HNO₃

C) H₃PO₄

D) HCl

E) HF

18. What is the molar mass of phosphoric acid (H₃PO₄)? (H = 1, P = 31, O = 16)

A) 96 g/mol

B) 98 g/mol

C) 100 g/mol

D) 102 g/mol

E) 104 g/mol

19. What is the molar mass of barium chloride (BaCl₂)? (Ba = 137, Cl = 35.5)

A) 202 g/mol

B) 208 g/mol

C) 210 g/mol

D) 207 g/mol

E) 215 g/mol

20. What is the molar mass of sodium carbonate (Na₂CO₃)? (Na = 23, C = 12, O = 16)

A) 100 g/mol

B) 105 g/mol

C) 110 g/mol

D) 98 g/mol

E) 108 g/mol

Answers with Explanations

1. C) 18.0 g/mol → H₂O = (2×1) + 16 = 18

2. B) CO₂ → C = 12, O₂ = 32 → total = 44

3. A) 58.5 g/mol → 23 (Na) + 35.5 (Cl) = 58.5

4. B) 180 g/mol → C₆H₁₂O₆ = (6×12) + (12×1) + (6×16) = 180

5. E) H₂ → 2×1 = 2 g/mol

6. C) 98 g/mol → H₂SO₄ = (2×1) + 32 + (4×16) = 98

7. A) 100 g/mol → 40 (Ca) + 12 (C) + 48 (O) = 100

8. A) H₂O₂ → (2×1) + (2×16) = 34

9. C) 16 g/mol → C = 12, H₄ = 4 → total = 16

10. C) 342 g/mol → (2×27) + (3×(32 + (4×16))) = 342

11. B) 46 g/mol → C₂H₆O = (2×12) + (6×1) + 16 = 46

12. E) All of the above → CO (12+16=28), N₂ (14×2=28), NO (14+16=30 close)

13. D) 28.0 g/mol → N = 14 × 2 = 28

14. B) 56 g/mol → K = 39, O = 16, H = 1 → total = 56

15. A) 148 g/mol → 24 + 2×(14 + (3×16)) = 148

16. A) 60 g/mol → CH₃COOH = (2×12) + (4×1) + (2×16) = 60

17. A) H₂SO₄ → Highest mass = 98 g/mol

18. A) 96 g/mol → H₃PO₄ = (3×1) + 31 + (4×16) = 96

19. A) 202 g/mol → 137 + (2×35.5) = 202

20. A) 106 g/mol → (2×23) + 12 + (3×16) = 106

Questions on Molar Mass: Practice Problems and Answer Key

Practical Classroom Applications

Teachers can use this topic in several ways:

Molar mass worksheets for guided and independent practice.
Stoichiometry review activities connecting mass and mole relationships.
Chemical formula exercises involving compounds and elements.
Group problem-solving sessions to develop quantitative reasoning skills.
Preparation for chemistry exams and standardized tests.
Laboratory activities involving measurements and calculations.
Real-world examples related to pharmaceuticals, materials science, and environmental chemistry.
Integration with mole conversions and chemical equations to reinforce fundamental chemistry concepts.

Explaining how molar mass calculations are applied in pharmaceutical development, industrial chemistry, environmental analysis, and laboratory research. Highlighting these applications helps readers recognize the importance of molar mass in scientific and technological fields.

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Ronaldo Silva: Professor and Specialist in Science Education from University Federal FLuminense/RJ, with over 25 years of teaching experience..

Questions on Molar Mass: Practice Problems and Answer Key