Apentix/AP Chemistry/Unit 4: Chemical Reactions/Question
AP Chemistrymediummcq1 pt

A 0.500 g sample of a metal M reacts with excess HCl to produce 245 mL of H2 gas at STP. If the reaction is M + 2HCl yields MCl2 + H2, what is the approximate molar mass of M?

A.24.4 g/mol
B.45.6 g/mol
C.12.2 g/mol
D.91.2 g/mol

Explanation

Core Concept

At STP, 245 mL H2 = 0.245/22.4 = 0.01094 mol H2. From the equation, mol M = mol H2 = 0.01094. Molar mass = 0.500/0.01094 = approx 45.7 g/mol.

Correct Answer

B45.6 g/mol

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