Question

Calcium hydride (CaH 2) reacts with water to form hydrogen gas:

CaH 2 (s) + 2H 2O (l) → Ca(OH) 2 (aq) + 2H 2 (g)

How many grams of CaH 2 are needed to generate 48.0 L of H 2 gas at a pressure of 0.888 atm and a temperature of 32 °C?

Answer 1

1st calculate mol of H2 formed

we have:

P = 0.888 atm

V = 48.0 L

T = 32.0 oC

= (32.0+273) K

= 305 K

find number of moles using:

P * V = n*R*T

0.888 atm * 48 L = n * 0.08206 atm.L/mol.K * 305 K

n = 1.703 mol

from reaction,

moles of CaH2 required = (1/2)*moles of H2

= (1/2)*1.703 mol

= 0.8515 mol

Molar mass of CaH2 = 1*MM(Ca) + 2*MM(H)

= 1*40.08 + 2*1.008

= 42.096 g/mol

we have below equation to be used:

mass of CaH2,

m = number of mol * molar mass

= 0.8515 mol * 42.096 g/mol

= 35.8 g

Answer: 35.8 g