Question

4. What mass of magnesium metal reacts with sulfuric acid to produce 225 ml of hydrogen gas at STP? Mg (s) + H2SO4 (aq) -> MgSO4 (aq) + H2 (g)

Answer 1

1st calculate mol of H2 produced

Given:

P = 1.0 atm

V = 225.0 mL

= (225.0/1000) L

= 0.225 L

T = 273.0 K

find number of moles using:

P * V = n*R*T

1 atm * 0.225 L = n * 0.08206 atm.L/mol.K * 273 K

n = 1.004*10^-2 mol

From reaction,

Mol of Mg reacted = mol of H2 produced

= 1.004*10^-2 mol

Molar mass of Mg = 24.31 g/mol

use:

mass of Mg,

m = number of mol * molar mass

= 1.004*10^-2 mol * 24.31 g/mol

= 0.2441 g

Answer: 0.244 g