Ammonia Fountain

Purpose:

To demonstrate the solubility of a gas and the effect of a gas pressure difference.

Materials:

• 1-hole rubber stopper to fit Erlenmeyer flask
• 1L boiling/round-bottom flask
• 2-hole rubber stopper to fit boiling/round-bottom flask
• 500mL Erlenmeyer flask
• Large plastic syringe
• Long U-shaped glass tube
• Long rubber hose
• Long straight glass tube
• Ring clamp
• Ring stand
• Short straight glass tube
• 600mL beaker

Reagents:

• Ammonium chloride (NH₄Cl_(s))
• Sodium hydroxide (NaOH_(s))
• Phenolphthalein indicator

Hazards and PPE:

• Ammonium chloride is a toxin and irritant. Handle with care.
• Sodium hydroxide is corrosive and toxic. Handle with care.
• Wear approved safety goggles and gloves.

Protocol:

Preparation

1. Demo setup should be as shown:
   1. 
2. Fill 600mL beaker with 500mL DI H₂O and add 3 drops phenolphthalein indicator.
3. Fill large syringe with DI H₂O.
4. Place long and u-shaped glass tubes into 2-hole rubber stopper as shown.
5. Attach rubber hose to u-shaped glass tube. Connect the other end of the hose to the short glass tube that’s in a 1-hole stopper.
6. Invert the round-bottom flask and insert the 2-hole stopper assembly suspended high enough that long glass tube is not in the beaker as shown.
7. Measure 16g NaOH_(s) and 20g NH₄Cl_(s) in separate weigh boats.
8. Right before demo is performed: In the fume hood, add both solids to the Erlenmeyer flask.
9. Add 20mL DI H₂O to Erlenmeyer flask and immediately stopper flask with the 1-hole rubber stopper.
10. Swirl the Erlenmeyer flask to aid in the reaction, causing ammonia gas to fill the RBF.
11. After ~20 seconds, disconnect hose from the Erlenmeyer’s glass tube and connect to syringe filled with DI H₂O. Immediately move entire setup to demonstration bench.

Demonstration

1. Lower round bottom flask so that long glass tube is submerged as far as possible into beaker of water and phenolphthalein.
2. To initiate the fountain, use the syringe to inject a small amount of water into the round-bottom flask.
3. Water will rise into the tube and will spray into the round-bottom flask as a pink fountain.

Additional Notes:

• Lecture bottles of ammonia gas are difficult to obtain, but can be substituted for the gas generator used here if you have on available.
• Ammonia is flammable and may form explosive mixtures with air. It is harmful if inhaled and can displace oxygen to cause rapid suffocation. Only use it in a fume hood. Ammonia causes severe skin burns and eye damage and is very toxic to aquatic life - never let it go down the drain.

Disposal:

• Solution should be neutralized before being washed down the sink with excess water.

Citations:

1. This demo was adapted by me for the demo library of the Chemistry department at the University of Illinois at Urbana-Champaign.