Question

One gram of an alloy of aluminium and magnesium when treated with excess of dil. HCl forms magnesium chloride, aluminium chloride and hydrogen. The evolved hydrogen, collected over mercury at 0°C has a volume of 1.20 litres at 0.92 atm. pressure. Calculate the composition of the alloy. [H = 1, Mg = 24, Al = 27]

Answer 1

The ionic reaction equation for the reaction is :

1.) Mg(s) + 2H⁺ (aq) —> Mg²⁺(aq) + H₂(g)

Mole ratio is 1 : 2

2.) 2Al(s) + 6H⁺(aq) —> 2Al³⁺(aq) + 3H₂(g)

Mole ratio is 1 : 3

1 mole of H₂ = 22.4 litres at stp

1.20 / 22.4 = 0.053 moles.

Moles of Mg = 0.05 / 2 = 0.025 moles

Mass is :

0.025 × 24 = 0.6g

Moles of Al = 0.05 / 3 = 0.01667 moles.

Mass is :

0.01667 × 27 = 0.45 g

Composition of the alloy :

0.45 + 0.6 = 1.05g

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