“Stoichiometry” MCQ with Answer Explanation.

61. How many grams of aluminum (Al) are needed to produce 4 moles of aluminum oxide (Al₂O₃)? (Molar mass of Al = 27 g/mol)

A) 54 g
B) 108 g
C) 216 g
D) 324 g

Answer: B) 216 g

Explanation: The reaction is 4Al + 3O₂ → 2Al₂O₃. To produce 4 moles of Al₂O₃, you need 8 moles of Al. Mass = 8 moles × 27 g/mol = 216 g.

62. In the reaction 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O, how many moles of CO₂ are produced from 2 moles of C₄H₁₀?

A) 4 moles
B) 8 moles
C) 10 moles
D) 12 moles

Answer: B) 8 moles

Explanation: The reaction indicates that 2 moles of C₄H₁₀ produce 8 moles of CO₂.

63. If 10 g of NaOH is dissolved in water, how many moles of NaOH are present? (Molar mass of NaOH = 40 g/mol)

A) 0.25 moles
B) 0.5 moles
C) 0.75 moles
D) 1 mole

Answer: B) 0.25 moles

Explanation: Moles = mass / molar mass = 10 g / 40 g/mol = 0.25 moles.

64. How many moles of H₂ are produced when 2 moles of Mg react with 2 moles of HCl? (Mg + 2HCl → MgCl₂ + H₂)

A) 1 mole
B) 2 moles
C) 3 moles
D) 4 moles

Answer: B) 2 moles

Explanation: The balanced equation indicates that 1 mole of Mg produces 1 mole of H₂, so 2 moles of Mg produce 2 moles of H₂.

65. What is the molar mass of sodium sulfate (Na₂SO₄)?

A) 126 g/mol
B) 142 g/mol
C) 150 g/mol
D) 178 g/mol

Answer: A) 142 g/mol

Explanation: Molar mass = (2×23) + (32) + (4×16) = 46 + 32 + 64 = 142 g/mol.

66. If 5 moles of CO₂ are produced, how many moles of glucose are needed? (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O)

A) 2.5 moles
B) 5 moles
C) 7.5 moles
D) 10 moles

Answer: B) 5 moles

Explanation: The balanced equation indicates that 1 mole of glucose produces 6 moles of CO₂, so to produce 5 moles of CO₂, you need (5/6) moles of glucose, which is approximately 0.83 moles.

67. In the reaction 2K + Cl₂ → 2KCl, how many grams of KCl are produced from 4 moles of K? (Molar mass of KCl = 74.5 g/mol)

A) 149 g
B) 298 g
C) 372 g
D) 448 g

Answer: B) 298 g

Explanation: 4 moles of K produce 4 moles of KCl. Mass = 4 moles × 74.5 g/mol = 298 g.

68. What is the volume of 3 moles of gas at STP? (1 mole = 22.4 L)

A) 22.4 L
B) 44.8 L
C) 67.2 L
D) 72.8 L

Answer: C) 67.2 L

Explanation: Volume = moles × volume per mole = 3 moles × 22.4 L/mole = 67.2 L.

69. How many grams of K₂SO₄ can be produced from the reaction of 2 moles of K with excess sulfuric acid? (K + H₂SO₄ → K₂SO₄ + H₂)

A) 94 g
B) 196 g
C) 228 g
D) 312 g

Answer: B) 196 g

Explanation: The balanced equation shows that 2 moles of K produce 1 mole of K₂SO₄. The molar mass of K₂SO₄ is 174 g/mol, so mass = 1 × 174 g = 174 g.

70. If 0.5 moles of Ca(OH)₂ are used, how many moles of water are produced? (Ca(OH)₂ + CO₂ → CaCO₃ + H₂O)

A) 0.5 moles
B) 1 mole
C) 2 moles
D) 3 moles

Answer: A) 0.5 moles

Explanation: The balanced equation shows that 1 mole of Ca(OH)₂ produces 1 mole of H₂O, so 0.5 moles of Ca(OH)₂ will yield 0.5 moles of H₂O.