Hydrogen: The Reducer

Why it matters

Pass hydrogen gas over heated black copper oxide. The powder turns reddish-brown, and water droplets form on the cool glass walls.

The idea in plain words

Analyze the displacement: Hydrogen takes oxygen, Copper is left behind.

Predict first

What role does hydrogen play in this reaction?

Hydrogen removes oxygen from the metal oxide, leaving pure metal behind. This makes hydrogen a reducing agent.

• It acts as an oxidizing agent by adding oxygen to copper.
• It acts as a reducing agent by removing oxygen from copper oxide. — correct
• It acts as a catalyst to speed up the heating.
• It simply washes the black dust away.

What you do

Test hydrogen on three different metal oxides. Observe the colour changes and note which metals are liberated.

Check yourself

In the reaction CuO + H₂ → Cu + H₂O, what is the visible evidence that a reaction occurred?

The verified observation for CuO + H₂ is the formation of reddish-brown copper metal.

Which of these hydrogen reductions need heat to proceed?

All three oxides are reduced only when heated — hydrogen is passed over the hot oxide (CuO + H₂ is heated too).

Why is hydrogen considered a reducing agent in these reactions?

Reduction is defined here as the removal of oxygen. Hydrogen takes the oxygen to form water, reducing the metal oxide to metal.

• The black powder turns into reddish-brown copper. — correct
• The copper oxide dissolves in water.
• Hydrogen gas turns into a solid.
• The test tube explodes.
• Only CuO + H₂
• All three — CuO, Fe₂O₃ and PbO — correct
• None — hydrogen reduces them at room temperature
• Only Fe₂O₃ and PbO
• Because it gains electrons from the metal.
• Because it removes oxygen from the metal oxide. — correct
• Because it is a gas.
• Because it produces water vapor.