Question

The hydrogen gas from the reaction: Zn(s) +2HCl(aq)->ZnCl2(aq)+H2(g) is bubbled through water for collection. 250mL of Hydrogen gas is collected at 25o Celsius. The total pressure is 1.032 atm. Calculate the partial pressure of the hydrogen gas and the mass of Zinc required to produce that gas. (The vapor pressure of water is 23.76 torr at 25oCelsius).

Answer 1

1)

Partial pressure of H2 = Total pressure - p(H2O)

= 1.032 atm - 23.76 torr

= 1.032 atm - 23.76/760 atm

= 1.032 atm - 0.0313 atm

= 1.001 atm

Answer: 1.001 atm

2)

1st calculate the mol of H2 formed

Given:

P = 1.001 atm

V = 250.0 mL

= (250.0/1000) L

= 0.25 L

T = 25.0 oC

= (25.0+273) K

= 298 K

find number of moles using:

P * V = n*R*T

1.001 atm * 0.25 L = n * 0.08206 atm.L/mol.K * 298 K

n = 1.023*10^-2 mol

Now from reaction,

number of mol of Zn = number of mol of H2 formed

= 1.023*10^-2 mol

Molar mass of Zn = 65.38 g/mol

use:

mass of Zn,

m = number of mol * molar mass

= 1.023*10^-2 mol * 65.38 g/mol

= 0.6688 g

Answer: 0.6688 g