How to Make Nitrous Oxide (Laughing Gas)

The procedure is safe if you follow the directions carefully

Nitrous oxide molecule
Laguna Design / Getty Images

You can easily make nitrous oxide, or laughing gas, in the lab or at home. However, there are reasons why you might want to forgo the preparation unless you have chem lab experience.

What Is Nitrous Oxide?

Nitrous oxide (N2O), also known as laughing gas, is a colorless, sweet-smelling, sweet-tasting gas that is used in dentistry and surgery because inhaling the gas produces analgesic and anesthetic effects. The gas is also used to improve the engine output of automotive vehicles and as an oxidizer in rocketry. Nitrous oxide got the name "laughing gas" because inhaling it produces euphoria.

How to Make It

English chemist Joseph Priestley first synthesized nitrous oxide in 1772 by collecting the gas produced from sprinkling nitric acid over iron filings. Nitrous oxide usually is produced by using the method developed by another English chemist, Humphry Davy, of gently heating ammonium nitrate to decompose it into nitrous oxide and water vapor:

NH4NO3 (s) → 2 H2O (g) + N2O (g)

The key here is gently heating the ammonium nitrate to between 170 degrees C and 240 degrees C because higher temperatures might cause the ammonium nitrate to detonate. People have been doing this without incident for more than 150 years, so the procedure is safe as long as you take care.

Next, cool the hot gases to condense the water. The best way to do this is by using a pneumatic trough, which involves a tube leading from the ammonium nitrate container that bubbles the gases up through water into a collection jar. You want the rate of gas production to be a bubble or two per second. The pneumatic trough removes the water from the reaction as well as smoke from impurities in the ammonium nitrate.

The gas in the collection jar is your nitrous oxide, plus lesser amounts of other nitrogen oxides, including nitric oxide and nitrogen monoxide. Nitric oxide eventually is oxidized to nitrous oxide upon exposure to oxygen, although acid and base treatments are used to remove impurities for commercial-scale production.

When your container is full of gas, discontinue heating the ammonium nitrate and disconnect the tubing so that water will not flow up into your collection container. Cover the container so that you can turn it upright without losing the gas. If you don't have a lid for the container, a flat sheet of glass or plastic will work fine.

Safety Precautions

How to keep the preparation safe:

  • Higher purity ammonium nitrate is more stable than ammonium nitrate that contains impurities, so safety improves if you begin with high-quality starting material.
  • Don't exceed 240 degrees C, or you'll risk explosive decomposition of the ammonium nitrate.
  • If you're using a direct heat source such as a thermostat-controlled burner, don't decompose the last bit of ammonium nitrate because it is more likely to overheat.
  • Nitrous oxide is a safe lab gas, but overexposure via inhalation may result in asphyxiation, in much the same way as overexposure to helium gas presents a risk.