Gas Stoichiometry with Magnesium

Calculating molar volume by reacting Mg with HCl

Gas Laws Intermediate (High School) 40 min ~$8.00

Objective

Determine the molar volume of hydrogen gas at room conditions by reacting a known mass of magnesium ribbon with excess hydrochloric acid.

Background

When magnesium reacts with HCl, hydrogen gas is produced: Mg + 2HCl → MgCl₂ + H₂. By measuring the mass of Mg used and the volume of H₂ collected, the molar volume at room conditions can be calculated and compared with the theoretical value at STP (22.4 L/mol).

Safety Warnings

  • HCl is corrosive
  • Hydrogen is flammable — no flames
  • Handle glassware carefully

Required PPE

goggles gloves lab_coat

Materials

  • Magnesium ribbon (0.1 g)
    Accurately weighed
  • Hydrochloric acid (HCl) (30 mL)
    2M, excess
  • Distilled water (500 mL)

Equipment

Eudiometer tube or graduated cylinder (50 mL) Pneumatic trough Copper wire cage Rubber stopper Analytical balance Thermometer Barometer

Procedure

1

Weigh a 3-4 cm strip of magnesium ribbon accurately. Record mass to 0.001 g.

3 min
2

Roll the Mg ribbon and secure it in a copper wire cage attached to a rubber stopper.

3 min
3

Fill the eudiometer tube with 2M HCl. Insert the stopper+Mg assembly, inverting the tube into the trough.

5 min Handle acid carefully
4

Allow the reaction to complete. All the Mg should dissolve, producing H₂ gas that collects at the top.

10 min No flames nearby
5

Equalize water levels inside and outside the tube. Read the gas volume at the meniscus.

3 min
6

Record room temperature and atmospheric pressure.

2 min
7

Correct for water vapor pressure. Calculate moles of H₂ from Mg mass. Determine molar volume.

8 min

Expected Results

0.1 g Mg = 0.00411 mol, producing 0.00411 mol H₂. At room conditions (~25°C, 1 atm), volume should be about 100 mL. Calculated molar volume at STP should be approximately 22.4 L/mol (±5%).

Cleanup

Neutralize remaining HCl with NaHCO₃. Dispose down the drain. Rinse all equipment.

Details

Category
Gas Laws
Difficulty
Intermediate (High School)
Duration
40 min
Est. Cost
$8.00
Steps
7
Materials
3

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Frequently Asked Questions

What is the objective of Gas Stoichiometry with Magnesium?
Determine the molar volume of hydrogen gas at room conditions by reacting a known mass of magnesium ribbon with excess hydrochloric acid.
How difficult is Gas Stoichiometry with Magnesium?
This experiment is rated as Intermediate (High School). It takes approximately 40 minutes to complete.
What safety precautions are needed for Gas Stoichiometry with Magnesium?
Key safety precautions include: HCl is corrosive; Hydrogen is flammable — no flames; Handle glassware carefully.
What materials are needed for Gas Stoichiometry with Magnesium?
The main materials required are: Magnesium ribbon, Hydrochloric acid (HCl), Distilled water.
What results should I expect from Gas Stoichiometry with Magnesium?
0.1 g Mg = 0.00411 mol, producing 0.00411 mol H₂. At room conditions (~25°C, 1 atm), volume should be about 100 mL. Calculated molar volume at STP should be approximately 22.4 L/mol (±5%).