“Stoichiometry” MCQ with Answer Explanation.

31. How many grams of potassium (K) are needed to react with 1 mole of Cl₂ to produce potassium chloride (KCl)? (Molar mass of K = 39 g/mol)

A) 39 g
B) 78 g
C) 117 g
D) 156 g

Answer: A) 39 g

Explanation: The reaction is 2K + Cl₂ → 2KCl, indicating that 1 mole of Cl₂ requires 1 mole of K. Thus, 39 g of K is needed.

32. 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: A) 0.17 moles

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

33. In the reaction 2H₂ + O₂ → 2H₂O, what is the mole ratio of H₂ to H₂O?

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

Answer: B) 2:1

Explanation: The balanced equation indicates that 2 moles of H₂ produce 2 moles of H₂O, giving a ratio of 2:2, which simplifies to 1:1.

34. If 5 moles of CH₄ are burned in oxygen, how many moles of CO₂ are produced? (CH₄ + 2O₂ → CO₂ + 2H₂O)

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

Answer: A) 5 moles

Explanation: The reaction shows that 1 mole of CH₄ produces 1 mole of CO₂, so 5 moles of CH₄ yield 5 moles of CO₂.

35. What is the mass of 2 moles of ethylene glycol (C₂H₆O₂)? (Molar mass of C₂H₆O₂ = 62 g/mol)

A) 62 g
B) 124 g
C) 186 g
D) 248 g

Answer: B) 124 g

Explanation: Mass = moles × molar mass = 2 moles × 62 g/mol = 124 g.

36. How many moles of O₂ are needed to react with 4 moles of NH₃ in the reaction: 4NH₃ + 5O₂ → 4NO + 6H₂O?

A) 4 moles
B) 5 moles
C) 6 moles
D) 10 moles

Answer: B) 5 moles

Explanation: According to the balanced equation, 4 moles of NH₃ react with 5 moles of O₂.

37. In the reaction 2K + Cl₂ → 2KCl, how many grams of chlorine are needed to react with 3 moles of K? (Molar mass of Cl₂ = 71 g/mol)

A) 71 g
B) 106 g
C) 142 g
D) 213 g

Answer: B) 106 g

Explanation: The balanced equation shows that 2 moles of K require 1 mole of Cl₂. Therefore, 3 moles of K require 3 × (1/2) = 1.5 moles of Cl₂, which equals 1.5 × 71 g/mol = 106.5 g.

38. What is the mass of 4 moles of sulfur (S)? (Molar mass of S = 32 g/mol)

A) 64 g
B) 128 g
C) 96 g
D) 112 g

Answer: C) 128 g

Explanation: Mass = moles × molar mass = 4 moles × 32 g/mol = 128 g.

39. If 8 moles of Ca(OH)₂ are used in a reaction, how many moles of water are produced? (Ca(OH)₂ + CO₂ → CaCO₃ + H₂O)

A) 2 moles
B) 4 moles
C) 8 moles
D) 16 moles

Answer: C) 8 moles

Explanation: The balanced equation shows that 1 mole of Ca(OH)₂ produces 1 mole of H₂O, so 8 moles of Ca(OH)₂ yield 8 moles of H₂O.

40. In the reaction 2C₆H₁₂ + 17O₂ → 12CO₂ + 12H₂O, how many grams of CO₂ are produced from 2 moles of C₆H₁₂? (Molar mass of CO₂ = 44 g/mol)

A) 528 g
B) 352 g
C) 264 g
D) 220 g

Answer: A) 528 g

Explanation: 2 moles of C₆H₁₂ produce 12 moles of CO₂. Mass = 12 moles × 44 g/mol = 528 g.