What mass of a divalent metal M (atomic mass = 40) would react with excess hydrochloric acid to liberate 224cm³ dry hydrogen gas measured at S.T.P?

JAMB Chemistry 2024 369 views
Source: JAMB · 2024

What mass of a divalent metal M (atomic mass = 40) would react with excess hydrochloric acid to liberate 224cm³ dry hydrogen gas measured at S.T.P?

  1. 8.0 g
  2. 4.0 g
  3. 0.8 g
  4. 0.4 g ✓
Explanation

A divalent metal reacts: M + 2HCl → MCl₂ + H₂. One mole of M gives one mole of H₂.

At S.T.P., one mole of gas is 22 400 cm³. Moles of H₂ = 224 ÷ 22 400 = 0.01 mol.

So moles of M = 0.01 mol. Mass = 0.01 × 40 = 0.4 g.

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