Question

The hydrogen gas produced by reaction between magnesium metal and hydrochloric acid is collected via water displacement. The gas in the collection flask has a volume of 0.0450 L at 25.0oC. If the atmospheric pressure is 755 torr, how many moles of hydrogen gas were collected. The vapor pressure of water at 25oC is 23.8 torr

Answer 1

pressure of hydrogen gas = 755 - 23.8 = 731.2 torr = 0.9621 atm

Use ideal gas equation for calculation of mole of gas

Ideal gas equation

PV = nRT             where, P = atm pressure = 0.9621 atm,

V = volume in Liter = 0.0450 L

n = number of mole = ?

R = 0.08205L atm mol^-1 K^-1 =Proportionality constant = gas constant,

T = Temperature in K = 25⁰C = 273.15+ 25 = 298.15 K

We can write ideal gas equation

n = PV/RT

Substitute the value

n = (0.9621 X 0.0450)/(0.08205 X 298.15) = 0.00176978 mole

0.00176978 mole of hydrogen gas were collected.