“Stoichiometry” MCQ with Answer Explanation.

11. What is the molar mass of carbon dioxide (CO₂)?

A) 44 g/mol
B) 22 g/mol
C) 30 g/mol
D) 18 g/mol

Answer: A) 44 g/mol

Explanation: Molar mass = C (12 g/mol) + O (16 g/mol) × 2 = 12 + 32 = 44 g/mol.

12. How many moles of O₂ are needed to completely react with 4 moles of C₃H₈ in the reaction C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O?

A) 5 moles
B) 10 moles
C) 15 moles
D) 20 moles

Answer: B) 10 moles

Explanation: The reaction shows that 1 mole of C₃H₈ reacts with 5 moles of O₂. Thus, 4 moles of C₃H₈ require 4 × 5 = 20 moles of O₂.

13. What is the empirical formula of a compound with a molecular formula C₆H₁₂O₆?

A) C₃H₆O₃
B) C₆H₁₂O₆
C) C₂H₄O₂
D) CH₂O

Answer: D) CH₂O

Explanation: The empirical formula is obtained by dividing the subscripts by their greatest common divisor (GCD), which is 6 in this case.

14. If 2 moles of sodium react with chlorine gas to produce sodium chloride, how many grams of sodium chloride can be produced? (Molar mass of NaCl = 58.5 g/mol)

A) 58.5 g
B) 117 g
C) 175.5 g
D) 235 g

Answer: B) 117 g

Explanation: 2 moles of Na produce 2 moles of NaCl. Mass of NaCl = 2 moles × 58.5 g/mol = 117 g.

15. In the reaction 4Fe + 3O₂ → 2Fe₂O₃, what is the mole ratio of Fe to O₂?

A) 4:3
B) 2:3
C) 3:4
D) 2:1

Answer: A) 4:3

Explanation: The balanced equation shows that 4 moles of Fe react with 3 moles of O₂, giving a ratio of 4:3.

16. How many grams of aluminum are required to produce 54 grams of aluminum oxide (Al₂O₃)? (Molar mass of Al = 27 g/mol, Al₂O₃ = 102 g/mol)

A) 27 g
B) 54 g
C) 81 g
D) 108 g

Answer: C) 81 g

Explanation: From the reaction 4Al + 3O₂ → 2Al₂O₃, 2 moles of Al₂O₃ require 4 moles of Al. Therefore, 54 g Al₂O₃ (0.529 moles) require 0.529 × 4 = 2.116 moles of Al, which equals 2.116 × 27 g/mol = 57 g.

17. If you have 6 moles of CaCO₃, how many moles of CO₂ are produced when it decomposes? (CaCO₃ → CaO + CO₂)

A) 3 moles
B) 6 moles
C) 9 moles
D) 12 moles

Answer: B) 6 moles

Explanation: The decomposition of 1 mole of CaCO₃ produces 1 mole of CO₂. Thus, 6 moles produce 6 moles of CO₂.

18. What is the mass of 3 moles of potassium bromide (KBr)? (Molar mass of KBr = 119 g/mol)

A) 297 g
B) 357 g
C) 357 g
D) 437 g

Answer: A) 357 g

Explanation: Mass = moles × molar mass = 3 moles × 119 g/mol = 357 g.

19. In the balanced equation N₂ + 3H₂ → 2NH₃, how many grams of nitrogen are needed to produce 68 g of ammonia (NH₃)? (Molar mass of NH₃ = 17 g/mol)

A) 14 g
B) 28 g
C) 42 g
D) 56 g

Answer: B) 28 g

Explanation: 68 g of NH₃ equals 4 moles (68 g / 17 g/mol). From the equation, 1 mole of N₂ produces 2 moles of NH₃, thus 2 moles of N₂ are needed, which is 2 × 28 g = 28 g.

20. What volume of 0.2 M NaOH is needed to completely neutralize 0.5 moles of H₂SO₄?

A) 250 mL
B) 500 mL
C) 750 mL
D) 1000 mL

Answer: C) 750 mL

Explanation: The reaction is H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O. To neutralize 0.5 moles of H₂SO₄, 1 mole of NaOH is required. Thus, 0.5 moles H₂SO₄ require 1 mole of NaOH, and volume = 1 mole / 0.2 M = 5 L = 750 mL.