Question

What is the mass of a piece of magnesium wire that produces 39.30 mL of hydrogen gas collected over water at 23.0 degrees Celsius and at a pressure of 752 torr?

Answer 1

volume = 39.30 mL = 0.0393 L

pressure = 752 torr = 0.990 atm

temperature = 23 + 273 = 296 K

from ideal gas law :

P V = n R T

0.990 x 0.0393 = n x 0.0821 x 296

n = 1.60 x 10^-3

moles of H2 = 1.60 x 10^-3

Mg + 2 HCl ---------------> MgCl2 + H2

moles of Mg = moles of H2

moles of Mg = 1.60 x 10^-3

molar mass of Mg = 24

mass of Mg = 1.60 x 10^-3 x 24

                   = 0.0384 g

mass of Mg = 0.0384 g