Determine the mass (in grams) of magnesium

Question

Determine the mass (in grams) of magnesium metal required to produce 40.0 mL of H2 with a

temperature of 26.9 oC and an atmospheric pressure of 745 mmHg. Be sure to take into

account water vapour using equation (3). Equation (3) n_H2= (P_atom - P_H2O)V_b/ RT

Answer 1

Mg + 2HCl => MgCl₂ + H₂

The balanced equation will be used to determine the grams of Mg used once we determine the moles of H₂ generated under the stated conditions. First take the atmospheric P of 745 mmHg and subtract the P_vapor of H₂O, 26.739 mmHg.

745 mmHg - 26.739 mmHg = 718.261 mmHg, then convert to atm, 718.261 mmHg x 1 atm/760 mmHg = 0.945 atm

Now use the ideal gas law equation to solve for moles of H₂.

(0.945 atm)(0.0400 L) = n (0.08206 Latm/Kmol)(299.9 K)

n = 0.00154 mol H₂

Convert mol H₂ to mol Mg to g Mg.

0.00154 mol H₂ x 1 mol Mg/1 mol H₂ x 24.31 g Mg/1 mol Mg = 0.0374 g Mg