Question

Aluminum reacts with excess hydrochloric acid to form aqueous aluminum chloride and 30.6 mL of hydrogen gas over water at 27°C and 751 mmHg. How many grams of aluminum reacted? The partial pressure of water at 27°C is 26.8 mmHg.

Answer 1

Let; We have given;

The volume of Hydrogen gas = 30.6mL =0.0306L

Temperature = 27^oC = 27 +273.15 = 300.15K

As, Hydrogen gas is over water;

Total Pressure = Vapour pressure of Water + Pressure of H₂ gas

751 mmHg = 26.8 mmHg + Pressure of H₂ gas

The pressure of H₂ gas = 751 mmHg -26.8 mmHg

= 724.2 mmHg

= 724.2 mmHg x (1 atm/ 760 mmHg) =0.9528 atm

Now; Using Ideal gas equation, to calculate the number of moles of H₂ gas as;

PV = nRT

n = PV/RT

= (0.9528 atm x 0.0306L)/(0.08206 L.atm/mol.K x 300.15K)

= 0.001184 moles of H₂ gas

Now, The balanced reaction between Al and HCl will be as;

2Al_(s) + 6HCl(_aq) 2AlCl₃(aq) + 3H₂(g)

Now, From the balanced reaction; We will calculate the number of moles of Aluminium from the number of moles of Hydrogen gas, by using the mole to mole ratio as;

0.001184 moles of H₂ gas x( 2 moles of Al/ 3 moles of H₂ gas) = 0.000789 moles of Al

Now; Converting these moles of Aluminium to Grams of Aluminium by using the molar mass as;

0.000789 moles of Al x ( 26.98 g/ 1mole) = 0.02129 g of Aluminium

So, 0.0213 g of Aluminium reacted.