Students should be able to recall a source for the nitrogen and a source…

The idea

The Haber process makes ammonia from nitrogen and hydrogen, so you must be able to name where each reactant comes from. Nitrogen is obtained from the air, which is about 78% nitrogen by volume; fractional distillation of liquid air separates it from oxygen and other gases. Hydrogen is usually obtained from natural gas (methane) by reaction with steam, though other sources exist. A useful memory hook is that nitrogen comes from the sky and hydrogen comes from fossil fuel. In an exam, a question may ask you to state one source for each gas, so learn one reliable source for nitrogen and one for hydrogen, and be ready to name the raw material rather than just the element.

What earns the marks

• Nitrogen is obtained from air, which is approximately 78% nitrogen by volume.
• Nitrogen can be separated from air by fractional distillation of liquid air.
• Hydrogen is commonly obtained from natural gas, which is mainly methane.
• Hydrogen can be produced by reacting methane with steam (steam reforming).
• The Haber process combines nitrogen and hydrogen to produce ammonia.
• A named raw material, such as air or natural gas, is a valid source in an exam answer.

Common mistakes and how to put them right

• Saying nitrogen comes from nitrogen fertiliser.

  Put it right: Nitrogen is obtained from air.

• Saying hydrogen comes from water with no named process.

  Put it right: Name natural gas or methane reacted with steam.

• Writing that nitrogen is made in the Haber process.

  Put it right: Nitrogen is a reactant obtained from air, while ammonia is the product.

Exam tips

• Learn one named source for each gas rather than several, so recall is quick and accurate.
• Use the phrase 'from air' for nitrogen and 'from natural gas' for hydrogen as a minimum secure answer.
• If asked to explain, link fractional distillation to separating nitrogen from liquid air, and steam reforming to producing hydrogen from methane.