The Determination of the Molar Volume of a Gas
SAMPLE DATA TABLE
*Mass of Mg (g)
Volume of flask (mL)
Maximum pressure (atm)
Initial pressure (atm)
Pressure change, ∆
Vapor pressure of water (atm)
22.1 mm Hg
= 0.02777 atm
Answer to PRE-LAB QUESTION
A reaction of 0.028 g of magnesium with excess hydrochloric acid generated 31.0 mL of gas.
The gas was collected by water displacement in a 22 °C water bath.
The barometric pressure that day was
746 mm Hg.
Use Dalton’s law and the vapor pressure of water at 22 °C (the table value is 19.8 mm Hg)
to calculate the partial pressure of hydrogen gas collected.
(b) Use the combined law to calculate the “corrected” volume of hydrogen gas collected at STP.
What is the theoretical number of moles of hydrogen that can be produced from
0.028 g of Mg?
(d) Divide the corrected volume of hydrogen by the theoretical number of moles of hydrogen to
calculate the molar volume (L/mol) of hydrogen at STP.
Adapted from Advanced Chemistry with Vernier & Laboratory Experiments for Advanced Placement Chemistry by Sally Ann Vonderbrink, Ph. D.