Question

When aluminum is placed in concentrated hydrochloric acid, hydrogen gas is produced.

Answer 1

Answer : The mass of aluminium (Al) is 0.413 g

Solution : Given,

Volume of $H_{2}(g)$ at STP = 513 ml = 0.513 L           ( 1 L = 1000 ml )

Molar mass of aluminium = 26.98 g/mole

First we have to calculate the moles of $H_{2}(g)$.

At STP,    

1 mole occupies 22.4 L volume

now, 0.513 L gives $\frac{1mole\times0.513L}{22.4L}$ moles of $H_{2}(g)$

The moles of $H_{2}(g)$ = 0.0229 moles

The Net balanced chemical reaction is,

$2Al(s)+6HCl(aq)\rightarrow 2AlCl_3(aq)+3H_2(g)$

From the balanced chemical reaction, we conclude that

2 moles of Aluminium (Al) produces 3 moles of hydrogen gas

Now the number of moles of aluminium required in 0.0229 moles of hydrogen gas = $\frac{2moles\times 0.0229moles}{3moles}$ = 0.0153 moles

Now we have to calculate the mass of aluminium.

Mass of aluminium = number of moles × Molar mass = 0.0153 moles × 26.98 g/mole = 0.413 g

The mass of aluminium required is 0.413 g.