Question

7.Aluminum cans can be converted into alum [KAl(SO4)2 · 12 H2O] and hydrogen gas via a very simple procedure summarized by the overall equation given below. Alum is a useful agent in water-proofing and hydrogen gas is a very useful fuel. An aluminum soda pop can with a mass of 19.56 g reacted with an excess of potassium hydroxide. What is the volume at STP of the hydrogen gas produced?

Answer 1

When aluminium reacts with NaOH (aq.), evolution of hydrogen gas takes place according to the following equation.

Given mass of aluminium is 19.56 gm. Since the atomic mass of Aluminium is 27, therefore moles of Aluminium in 19.56 gm will be 19.56 / 27 = 0.724 moles.

From the equation, it is clear that,

1 mole of aluminium gives = 1.5 moles of H₂ gas

therefore 0.724 moles of aluminium will give = 1.5 x 0.724 moles of H₂.

As 1 mole of any gas at STP occupies 22.4 L volume (assuming ideal behaviour), 1.5 x 0.724 moles of H₂ gas will occupy 22.4 x 1.5 x 0.724 L (= 24.3264 L) at STP.