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How to Make Nitrous Oxide or Laughing Gas

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How to Make Nitrous Oxide or Laughing Gas
Nitrous oxide is prepared by decomposing ammonium nitrate to produce nitrous oxide and water vapor.

Nitrous oxide is prepared by decomposing ammonium nitrate to produce nitrous oxide and water vapor. Note that is critical to keep the temperature below 240 Celsius.

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

What Is Nitrous Oxide or Laughing Gas?

Nitrous oxide (N2O) is also known as laughing gas. It is a colorless sweet-smelling and 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 produce the engine output of automotive vehicles and as an oxidizer in rocketry. Nitrous oxide gets the name "laughing gas" because inhaling it produces euphoria.

How to Make Nitrous Oxide or Laughing Gas

Joseph Priestley first synthesized nitrous oxide in 1772 by collecting the gas produced from sprinkling nitric acid over iron filings, however, nitrous oxide usually is produced using Humphry Davy's method 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°C and 240°C, because higher temperatures may cause the ammonium nitrate to detonate. People have been doing this without incident for over 150 years, so the procedure is safe as long as you take care.

Next, the hot gases are cooled to condense the water. The best way to do this is 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 or laughing gas, plus lesser amounts of other nitrogen oxides, including nitric oxide or 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 of nitrous oxide. 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 works fine.

Safety Precautions

  • Higher purity ammonium nitrate is more stable than ammonium nitrate that contains impurities, so safety improves if you start with high quality starting material.

  • Don't exceed 240°C or you'll risk explosive decomposition of the ammonium nitrate.

  • If you are using a direct heat source, such as a thermostat controlled burner, don't decompose the last bit of ammonium nitrate since 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.

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