“Stoichiometry” MCQ with Answer Explanation.

41. How many grams of glucose (C₆H₁₂O₆) are needed to produce 4 moles of ethanol (C₂H₅OH)? (C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂)

A) 90 g
B) 180 g
C) 360 g
D) 720 g

Answer: C) 720 g

Explanation: From the reaction, 1 mole of glucose produces 2 moles of ethanol. Thus, 4 moles of ethanol require 2 moles of glucose. Mass = 2 moles × 180 g/mol = 360 g.

42. What is the percentage composition of hydrogen in water (H₂O)?

A) 33%
B) 11%
C) 22%
D) 67%

Answer: A) 11%

Explanation: The molar mass of H₂O is 18 g/mol. The mass of H is 2 g, so the percentage is (2/18) × 100 = 11.11%.

43. If 0.5 moles of H₂ react with excess O₂, how many moles of water (H₂O) will be produced? (2H₂ + O₂ → 2H₂O)

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

Answer: B) 0.5 moles

Explanation: From the balanced equation, 2 moles of H₂ produce 2 moles of H₂O, so 0.5 moles of H₂ will produce 0.5 moles of H₂O.

44. What is the molar mass of potassium nitrate (KNO₃)?

A) 85 g/mol
B) 120 g/mol
C) 146 g/mol
D) 196 g/mol

Answer: C) 101 g/mol

Explanation: Molar mass = (39) + (14) + (3 × 16) = 39 + 14 + 48 = 101 g/mol.

45. In the reaction 2Na + Cl₂ → 2NaCl, how many moles of NaCl are formed from 3 moles of Na?

A) 1.5 moles
B) 2 moles
C) 3 moles
D) 4.5 moles

Answer: B) 3 moles

Explanation: The reaction shows that 2 moles of Na produce 2 moles of NaCl, so 3 moles of Na produce 3 moles of NaCl.

46. How many grams of oxygen are needed to react with 2 moles of hydrogen? (2H₂ + O₂ → 2H₂O; Molar mass of O₂ = 32 g/mol)

A) 16 g
B) 32 g
C) 48 g
D) 64 g

Answer: B) 32 g

Explanation: The balanced equation indicates that 2 moles of H₂ react with 1 mole of O₂, so for 2 moles of H₂, you need 1 mole of O₂, which equals 32 g.

47. If 10 g of NaCl is dissolved in water, how many moles of NaCl are present? (Molar mass of NaCl = 58.5 g/mol)

A) 0.17 moles
B) 0.25 moles
C) 0.5 moles
D) 1 mole

Answer: B) 0.17 moles

Explanation: Moles = mass / molar mass = 10 g / 58.5 g/mol ≈ 0.171 moles.

48. What is the volume of 4 moles of gas at STP? (1 mole = 22.4 L)

A) 44.8 L
B) 67.2 L
C) 89.6 L
D) 100 L

Answer: C) 89.6 L

Explanation: Volume = moles × volume per mole = 4 moles × 22.4 L/mole = 89.6 L.

49. How many grams of Na₂SO₄ can be produced from the reaction of 2 moles of Na with excess sulfuric acid? (2Na + H₂SO₄ → Na₂SO₄ + H₂)

A) 74 g
B) 142 g
C) 196 g
D) 252 g

Answer: B) 142 g

Explanation: The balanced equation shows that 2 moles of Na produce 1 mole of Na₂SO₄. The molar mass of Na₂SO₄ is 142 g/mol, so mass = 1 × 142 g = 142 g.

50. If 4 moles of CO₂ are produced, how many moles of glucose are needed? (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O)

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

Answer: B) 2 moles

Explanation: 1 mole of glucose produces 6 moles of CO₂, so to produce 4 moles of CO₂, you need (4/6) = 0.67 moles of glucose.