Question

Zinc metal reacts with hydrochloric acid according to the following balanced equation.
Zn(s) + 2HCl(aq) -> ZnCl2(aq) + H2(g)

the hydrogen gas is collected over water at a temperature of 20.0 degrees celsius and a total pressure of 775.2 mmHg. a total of 1.85 L of gas is collected. the vapor pressure of water at 20.0 degrees celsius is 17.55 mmHg. what is the mass of hydrogen gas (in grams) formed

Answer 1

Zn(s) + 2HCl(aq) -> ZnCl2(aq) + H2(g)

dry H2 gas pressure = total pressure of the gas - the vapor pressure of water at 20.0 degrees celsius

                             = 775.2 - 17.55

                              = 757.65 mm Hg

pressure of dry H2 gas in atm. = 0.997 atm.

according to PV = nRT ==> PV = (mass/mol.wt)*RT

   mass = P*V*mol.wt/RT

mass =( 0.997*1.85*2)/(0.0821*293)

mass = 0.153 gm.

mass of H2 gas = 0.153 gm.