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
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.
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