BST 121-3 General Chemistry – Bachelor of Biosystems Technology
Faculty of Technological Studies Uva Wellassa University
BST 121-3
Experiment 5
Determination of the Relative Atomic Mass of Magnesium Using the Molar Volume of
Hydrogen Gas
Prelab Questions
1. Write the ideal gas law
2. Calculate the number of moles of hydrogen gas contained in a 20.00 cm-3 volume at 1
atm pressure and 27 oC temperature. (Universal gas constant is 8.314 J mol-1 K-1 or
0.0821 atm. dm-3 mol-1 K-1)
3. Balance the following equation and calculate how many HCl moles are required to react
with 1g of magnesium
Mg(s) + HCl (aq) MgCl2 (aq) + H2 (g)
4. Calculate how many moles of H2 are produced by reacting 1g of Mg with excess HCl
1. Theory
In this experiment, a known amount of magnesium is reacted with dilute hydrochloric acid to
produce hydrogen gas. Produced hydrogen gas is collected by the downward displacement of
water as shown in the following diagram. If you know the collected volume of the gas, pressure,
and temperature, the number of moles of Hydrogen gas produced can be calculated using the
ideal gas law.
PV = nRT (Ideal Gas Law)
Then using the balanced equation and stoichiometry between the Hydrogen gas and Mg, it is
possible to find the relative atomic mass of the Mg metal.
2. Procedure:
1) Prepare the apparatus as shown in the figure. The neck of the round bottom flask should
tighten up with a cork so that no air enters from the outside and no leakage of air is
produced inside
Experiment 5
1
Faculty of Technological Studies Uva Wellassa University
BST 121-3
Experiment 5
Determination of the Relative Atomic Mass of Magnesium Using the Molar Volume of
Hydrogen Gas
Prelab Questions
1. Write the ideal gas law
2. Calculate the number of moles of hydrogen gas contained in a 20.00 cm-3 volume at 1
atm pressure and 27 oC temperature. (Universal gas constant is 8.314 J mol-1 K-1 or
0.0821 atm. dm-3 mol-1 K-1)
3. Balance the following equation and calculate how many HCl moles are required to react
with 1g of magnesium
Mg(s) + HCl (aq) MgCl2 (aq) + H2 (g)
4. Calculate how many moles of H2 are produced by reacting 1g of Mg with excess HCl
1. Theory
In this experiment, a known amount of magnesium is reacted with dilute hydrochloric acid to
produce hydrogen gas. Produced hydrogen gas is collected by the downward displacement of
water as shown in the following diagram. If you know the collected volume of the gas, pressure,
and temperature, the number of moles of Hydrogen gas produced can be calculated using the
ideal gas law.
PV = nRT (Ideal Gas Law)
Then using the balanced equation and stoichiometry between the Hydrogen gas and Mg, it is
possible to find the relative atomic mass of the Mg metal.
2. Procedure:
1) Prepare the apparatus as shown in the figure. The neck of the round bottom flask should
tighten up with a cork so that no air enters from the outside and no leakage of air is
produced inside
Experiment 5
1
