By David Ward, Updated Aug 30, 2022

Overview

Nitrogen gas (N₂) is the most abundant gas in Earth’s atmosphere, yet isolating it in a laboratory setting requires careful handling of reagents and equipment. The following procedures demonstrate two proven, closed‑system methods that can be performed safely in a standard chemistry lab.

Required Equipment

• Erlenmeyer flask or bulb (1–250 mL)
• Stand and clamp to secure the flask
• Stopper with two 1 mm holes (or a standard stopper with tubing fittings)
• Glass tubing (1 mm diameter)
• Water‑cooled condenser (20–30 mm inner diameter)
• Cold water supply (room temperature to 15 °C)
• Closed collection vessel (glass or plastic)
• Heat source (Bunsen burner, hot plate, or oil bath)
• Reagents: ammonium chloride (NH₄Cl), sodium nitrate (NaNO₂), ammonia (NH₃)
• Optional: safety shield, fume hood, explosion vent

Procedure 1: Decomposition of Ammonium Nitrite (NH₄NO₂)

Ammonium nitrite is generated in situ from a 1:1 molar mixture of ammonium chloride and sodium nitrate. The reaction proceeds with the release of nitrogen gas and water vapor, while the condenser captures condensate and maintains a closed system.

Step 1 – Preparation

Weigh equimolar amounts of NH₄Cl and NaNO₂ (e.g., 5 g each for a 25 mL flask). Transfer the solids into the flask and add ~20 mL of deionized water. Stir until the mixture is fully dissolved.

Step 2 – Assembly

Insert the two‑hole stopper, attaching one end of the glass tubing to the stopper and the other end to the condenser. Connect the condenser to a continuous water supply and secure the condenser to a cooling bath. Attach the collection vessel to the condenser outlet.

Step 3 – Initiation

Turn on the water flow to the condenser and gently heat the flask using a Bunsen burner or hot plate set to low heat (≈70 °C). Gradually increase the temperature to 120 °C to drive the decomposition.

Step 4 – Collection

As nitrogen gas forms, it will rise through the condenser and be collected in the vessel. Monitor the pressure gauge (if installed) to ensure it remains below 2 atm. Once gas evolution ceases (typically 10–15 min), cease heating and allow the system to cool before disassembling.

Procedure 2: Reverse Haber Process (NH₃ → N₂ + H₂)

Ammonia can be thermally cracked to yield nitrogen and hydrogen gases. This method requires careful temperature control and handling of hydrogen, which is flammable.

Step 1 – Loading

Fill the flask with 20–30 mL of concentrated NH₃ solution or gaseous ammonia, ensuring all seals are tight.

Step 2 – Assembly

As before, attach the two‑hole stopper, glass tubing, condenser, and collection vessel. Verify that the condenser is well‑capped to prevent vapor escape.

Step 3 – Heating

Heat the flask gradually to 400–500 °C. Use a calibrated temperature controller to avoid sudden spikes. Maintain the temperature for 5–10 min, allowing the reaction to reach completion.

Step 4 – Safety Checks

Observe the collection vessel for hydrogen accumulation. If the vessel is pressurized beyond 1 atm, vent carefully or transfer the gas to a hydrogen‑safe container. Never expose the mixture to open flame.

Safety Considerations

• All experiments must be conducted inside a fume hood or well‑ventilated area.
• Use explosion‑proof apparatus and keep all materials away from ignition sources.
• Ammonium nitrite and ammonium nitrate are highly unstable; only the in‑situ generated mixture should be used.
• Hydrogen gas is flammable; collect it in a dedicated, grounded vessel and keep it away from heat.
• Wear appropriate PPE: goggles, lab coat, gloves, and a face shield if working with large quantities.
• Dispose of any residual ammonium salts according to local hazardous waste regulations.

TL;DR

Using a water‑cooled condenser keeps the system closed and controls pressure, while gradual heating enhances safety and yields pure nitrogen gas.

Conclusion

Both the decomposition of ammonium nitrite and the reverse Haber process provide reliable, reproducible routes to nitrogen gas when performed with proper safety precautions and equipment. Adhering to these protocols ensures experimental integrity and protects laboratory personnel.