Preparing and Testing Hydrogen Gas

Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★★☆ Some safety precautions required to perform safely

Categories: Elements and Periodic Table, Gases

Alternative titles: Laboratory Preparation of Hydrogen

Summary

Hydrogen gas is produced when zinc reacts with hydrochloric acid. The gas is collected over water and tested with a lit splint, which produces a distinctive ‘pop’ sound, confirming the presence of hydrogen.

Procedure

Place about 2.5 g of zinc (or magnesium ribbon) into a conical flask with a side arm.
Connect a thistle funnel and delivery tube to the flask, ensuring the delivery tube leads into a basin of water.
Invert three water-filled gas jars (or test tubes) in the water basin, ready to collect the gas.
Pour 50 cm³ of 1 M hydrochloric acid through the thistle funnel into the flask.
After ~5 seconds, place a gas jar over the end of the delivery tube and allow hydrogen to displace the water until the jar is full. Keep the jar inverted in water to retain the gas.
Collect three jars of hydrogen in this way.
Test one jar by bringing a lit wooden splint to the mouth of the jar — a squeaky pop confirms hydrogen.

Links

Making and testing hydrogen - WTN Chemistry Clips:

Preparation of Hydrogen gas in the Laboratory | Zinc metal and Dilute acid reaction - ThomasTKtungnung:

📄 Making hydrogen gas - BBC Bitesize: https://www.bbc.co.uk/bitesize/guides/z6qq47h/revision/3

Variations

Use magnesium ribbon instead of zinc to compare reaction speed.
Try collecting hydrogen using a gas syringe instead of water displacement.
Collect using an inverted test tube - the hydrogen rises to fill it.
Compare the pop sound from pure hydrogen vs. hydrogen mixed with air.

Safety Precautions

Wear goggles and gloves - hydrochloric acid is corrosive.
Collect gas carefully; avoid leaks, as hydrogen is highly flammable.
Do not ignite gas directly from the delivery tube.
Use small quantities of acid and metal to prevent vigorous reactions.

Questions to Consider

What is the balanced chemical equation for this reaction? (Zn + 2HCl → ZnCl₂ + H₂)
Why must the gas be collected upside down? (Hydrogen is lighter than air and would escape otherwise.)
What does the squeaky pop test show? (It confirms the presence of hydrogen, which burns with a small explosion.)
Why is hydrogen considered a potential fuel? (It produces only water when burned, making it a clean energy source.)