Zinc metal reacts with HCl as follows: Zn + 2 HCl ⇒ ZnCl2 + H2 What mass of zinc metal is needed to produce 600.0 mL of hydrogen gas collected over water at 30.0°C and at 775 mmHg?

it is required a mass of Zn equal to m = 1.608 gr of Zn

Explanation:

Assuming that the hydrogen behaves as an ideal gas (in reality it has positive deviations from the gas law, but we can neglect the small correction), then

P*V=n*R*T

n = P*V / (R*T)

where

P = absolute pressure = 775 mmHg = 1.02 atm

T = absolute temperature = 30°C+273 = 303 K

V = volume = 600 mL = 0.6 L

R = ideal gas constant = 0.082 atm*L / (mol*K)

n = number of moles of H₂ gas

replacing values

n = P*V / (R*T) = 1.02 atm*0.6 L / (0.082 atm*L / (mol*K) * 303 K) = 0.0246 moles of H₂

from the reaction

Zn + 2 HCl ⇒ ZnCl2 + H2

since 1 mole of H2 requires 1 mole of Zn to react, then

m = nz * M

where

nz = number of moles of zinc = number of moles of H₂ gas = 0.0246 moles

M = molecular weight of zinc = 65.38 gr/mol

m = mass of zinc required

therefore

m = 0.0246 moles * 65.38 gr/mol = 1.608 gr of Zn

m = 1.608 gr of Zn