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Veeni thermally decomposed 90 g of potassium chlorate of 60% purity. The total gas produced was allowed to react with hydrogen that was prepared by passing steam over hot magnesium metal. Calculate the amount of magnesium required to produce just sufficient hydrogen for completion of the reaction.

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Given KCIO3 = 90 gm (60% purity)

Oxygen gas will be produced on decomposition of KCIO3.

2 moles of KCIO3 gives 3 moles O2 

∴ 0.44 moles of KCIO3 will give = 3/2 x 0.44 moles of O2 = 0.66 moles of O2 

When O2 reacts with H2 , it gives H2O.

O2 + 2H2 → 2H2O

One mole of oxygen require 2 moles of H2.

∴ 0.66 mole O2 required = 0.66 × 2 = 1.32 mole of H2 required

For the production of H2 gas steam is passed over hot Mg metal.

1 mole of H2 will be obtained from 24 gm Mg.

∴ 1.32 mole of H2 will require = 24 × 1.32 gm = 31. 68 gm Mg.

∴ 31.68 gm Mg metal is required.

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