Conversions Between Mass and Number of Particles: Questions and Answer Key

Questions on Conversions Between Mass and Number of Particles

Converting between mass and the number of particles is a fundamental skill in chemistry because it links measurable quantities with atoms, molecules, and formula units. Developed by a Science Teacher and Education Specialist, this collection of questions combines scientific accuracy with practical classroom experience. The exercises are designed to help teachers, homeschool educators, and students build confidence in quantitative chemistry and prepare effectively for exams.

Conversions between mass and the number of particles involve the use of molar mass and Avogadro's number to relate macroscopic measurements to microscopic entities. By converting grams to moles and then moles to particles, chemists can determine the number of atoms, molecules, or ions present in a sample. This concept is essential for stoichiometry, chemical equations, and quantitative analysis.

 Multiple-Choice Questions: Conversions Between Mass and Number of Particles

    1. How many molecules are in 18.0 g of water (H₂O)?

A) 1.00 × 10²²

B) 6.02 × 10²³

C) 3.01 × 10²³

D) 1.20 × 10²⁴

E) 9.03 × 10²³

    2. How many atoms are in 12.0 g of carbon? (C = 12.0 g/mol)

A) 6.02 × 10²³

B) 3.01 × 10²³

C) 1.00 × 10²³

D) 2.00 × 10²³

E) 1.20 × 10²⁴

    3. What is the number of formula units in 58.5 g of NaCl? (NaCl = 58.5 g/mol)

A) 6.02 × 10²³

B) 1.20 × 10²⁴

C) 3.01 × 10²³

D) 5.02 × 10²²

E) 2.00 × 10²³

    4. How many oxygen atoms are in 36.0 g of water? (H₂O = 18.0 g/mol)

A) 6.02 × 10²³

B) 1.20 × 10²⁴

C) 2.41 × 10²⁴

D) 3.01 × 10²³

E) 2.00 × 10²³

    5. How many hydrogen atoms are in 18.0 g of water?

A) 6.02 × 10²³

B) 1.20 × 10²⁴

C) 2.41 × 10²⁴

D) 1.20 × 10²³

E) 4.00 × 10²³

    6. How many molecules are in 90.0 g of glucose (C₆H₁₂O₆, M = 180 g/mol)?

A) 3.01 × 10²³

B) 6.02 × 10²²

C) 1.20 × 10²⁴

D) 9.03 × 10²³

E) 2.00 × 10²³

    7. How many atoms are in 4.00 g of He? (He = 4.00 g/mol)

A) 2.00 × 10²³

B) 6.02 × 10²³

C) 4.00 × 10²³

D) 1.50 × 10²⁴

E) 8.00 × 10²³

    8. How many total atoms are in 1 molecule of H₂SO₄?

A) 4

B) 6

C) 7

D) 5

E) 2

    9. How many total atoms are in 98.0 g of H₂SO₄? (M = 98.0 g/mol)

A) 6.02 × 10²³

B) 3.01 × 10²⁴

C) 4.21 × 10²⁴

D) 7.00 × 10²³

E) 8.43 × 10²⁴

    10. How many formula units are in 100.0 g of CaCO₃? (M = 100.0 g/mol)

A) 6.02 × 10²³

B) 1.20 × 10²⁴

C) 3.01 × 10²³

D) 4.00 × 10²³

E) 8.00 × 10²²

    11. What is the number of atoms in 2.0 mol of copper? (Cu = 63.5 g/mol)

A) 6.02 × 10²³

B) 1.20 × 10²⁴

C) 3.00 × 10²³

D) 2.00 × 10²³

E) 9.03 × 10²³

    12. How many particles are in 0.50 mol of any substance?

A) 3.01 × 10²³

B) 1.00 × 10²³

C) 6.02 × 10²³

D) 1.20 × 10²⁴

E) 2.50 × 10²³

    13. How many oxygen atoms are in 1 mol of CO₂?

A) 1.00 × 10²³

B) 6.02 × 10²³

C) 1.20 × 10²⁴

D) 3.01 × 10²³

E) 2.00 × 10²⁴

    14. How many particles are in 4.00 g of H₂? (H₂ = 2.00 g/mol)

A) 6.02 × 10²³

B) 1.20 × 10²⁴

C) 3.01 × 10²³

D) 9.03 × 10²³

E) 2.00 × 10²³

    15. What is the number of water molecules in 9.0 g of water?

A) 3.01 × 10²³

B) 6.02 × 10²²

C) 2.00 × 10²³

D) 1.20 × 10²⁴

E) 9.03 × 10²³

    16. What is the total number of atoms in 1 mol of CH₄?

A) 2

B) 5

C) 6.02 × 10²³

D) 3

E) 10

    17. How many molecules are in 0.25 mol of CO₂?

A) 1.50 × 10²³

B) 2.00 × 10²³

C) 6.02 × 10²²

D) 3.01 × 10²³

E) 1.20 × 10²³

    18. How many atoms are in 0.25 mol of CO₂?

A) 3.01 × 10²³

B) 4.00 × 10²³

C) 1.50 × 10²³

D) 2.00 × 10²³

E) 2.25 × 10²³

    19. How many atoms are in 28.0 g of nitrogen gas (N₂)? (M = 28.0 g/mol)

A) 6.02 × 10²³

B) 1.20 × 10²⁴

C) 3.01 × 10²³

D) 2.00 × 10²³

E) 4.00 × 10²³

    20. How many Cl⁻ ions are in 2 mol of CaCl₂?

A) 1.00 × 10²⁴

B) 6.02 × 10²³

C) 2.00 × 10²⁴

D) 1.20 × 10²⁴

E) 3.01 × 10²³

  Answers with Explanations

    1. B) 6.02×10²³ — 18.0 g H₂O is 1 mol; 1 mol = Avogadro’s number of molecules

    2. A) 6.02×10²³ — 12.0 g C = 1 mol = Avogadro’s number of atoms

    3. A) 6.02×10²³ — 58.5 g NaCl = 1 mol = 6.02×10²³ formula units

    4. B) 1.20×10²⁴ — 36.0 g = 2 mol H₂O → 2 mol × 1 O atom/mol = 2 mol O atoms = 1.20×10²⁴

    5. C) 2.41×10²⁴ — 2 mol H₂O = 4 mol H → 4 × 6.02×10²³ = 2.41×10²⁴

    6. A) 3.01×10²³ — 90.0 g = 0.5 mol → 0.5 × 6.02×10²³

    7. B) 6.02×10²³ — 4.00 g He = 1 mol = Avogadro’s number

    8. C) 7 atoms — H₂ (2) + S (1) + O₄ (4) = 7

    9. B) 3.01×10²⁴ — 1 mol H₂SO₄ = 7 atoms → 6.02×10²³ × 7 = 4.21×10²⁴

    10. A) 6.02×10²³ — 100.0 g = 1 mol = Avogadro’s number

    11. B) 1.20×10²⁴ — 2 mol × 6.02×10²³

    12. A) 3.01×10²³ — 0.5 × 6.02×10²³

    13. C) 1.20×10²⁴ — 1 mol CO₂ = 2 mol O atoms = 2 × 6.02×10²³

    14. B) 1.20×10²⁴ — 4.00 g H₂ = 2 mol → 2 × 6.02×10²³

    15. A) 3.01×10²³ — 9.0 g H₂O = 0.5 mol → 0.5 × 6.02×10²³

    16. B) 5 atoms — CH₄ = 1 C + 4 H = 5 atoms

    17. A) 1.50×10²³ — 0.25 mol × 6.02×10²³

    18. B) 4.00×10²³ — 0.25 mol CO₂ = 0.25 mol C + 0.50 mol O → 0.75 mol atoms = 4.52×10²³

    19. B) 1.20×10²⁴ — 28.0 g N₂ = 1 mol N₂ = 2 mol N atoms → 1.20×10²⁴

    20. C) 2.00×10²⁴ — 2 mol CaCl₂ = 4 mol Cl⁻ → 4 × 6.02×10²³ = 2.41×10²⁴

• Questions on Conversions Between Moles and Gas Volume
• Questions on Molar Mass
• Questions on Gas Density

Practical Classroom Applications

Teachers can apply this topic through:

Mass and particle conversion worksheets for guided practice.

Stoichiometry review lessons connecting moles, mass, and particles.

Activities involving Avogadro's number to visualize extremely large quantities.

Group problem-solving exercises that develop quantitative reasoning skills.

Preparation for chemistry tests and standardized examinations.

Laboratory calculations related to reactants and products in chemical reactions.

Real-world applications involving pharmaceuticals, nanotechnology, and materials science.

Interactive classroom activities using dimensional analysis and conversion factors.

Discussing how conversions between mass and particles are used in chemical manufacturing, medicine, environmental analysis, and scientific research. Showing these practical applications helps students understand the importance of the mole concept and quantitative chemistry in everyday life and industry.

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