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JEE Main PYQs Mole Concept – Some Basic Concepts of Chemistry | NEET JEE Rankers

Mass of magnesium required to produce 220 mL of hydrogen gas at STP on reaction with excess of dilute HCl is

Given: Molar mass of Mg is 24 g mol⁻¹.

A. 0.24 mg
B. 235.7 g
C. 2.444 g
D. 236 mg

Step by Step Solution

Step 1: At STP, 1 mole of any gas occupies 22.4 L.

Step 2: Volume of hydrogen gas given = 220 mL = 0.220 L.

Step 3: Moles of H₂ produced = 0.220 / 22.4 = 0.00982 moles.

Step 4: Reaction involved:
Mg + 2HCl → MgCl₂ + H₂

Step 5: 1 mole of Mg produces 1 mole of H₂.
So, moles of Mg required = 0.00982 moles.

Step 6: Mass of Mg required = 0.00982 × 24 = 0.2357 g.

Step 7: 0.2357 g ≈ 236 mg.

✅ Final Answer: 236 mg