Question

When 4.03 g of aluminum is reacted with 54.3 mL of a 1.43 M solution of HCl, the resulting gas was collected in a 0.540 liter vessel at 30.7°C. What is the pressure (in atm) of hydrogen gas inside the vessel.

Answer 1

Molar mass of Al = 26.98 g/mol

mass(Al)= 4.03 g

use:

number of mol of Al,

n = mass of Al/molar mass of Al

=(4.03 g)/(26.98 g/mol)

= 0.1494 mol

volume of HCl, V = 54.3 mL

= 5.43*10^-2 L

use:

number of mol in HCl,

n = Molarity * Volume

= 1.43*5.43*10^-2

= 7.765*10^-2 mol

Balanced chemical equation is:

2 Al + 6 HCl ---> 3 H2 + 2 AlCl3

2 mol of Al reacts with 6 mol of HCl

for 0.1494 mol of Al, 0.4481 mol of HCl is required

But we have 7.765*10^-2 mol of HCl

so, HCl is limiting reagent

we will use HCl in further calculation

According to balanced equation

mol of H2 formed = (3/6)* moles of HCl

= (3/6)*7.765*10^-2

= 3.882*10^-2 mol

Given:

V = 0.54 L

n = 3.882E-2 mol

T = 30.7 oC

= (30.7+273) K

= 303.7 K

use:

P * V = n*R*T

P * 0.54 L = 0.0388 mol* 0.08206 atm.L/mol.K * 303.7 K

P = 1.7916 atm

Answer: 1.79 atm