White Smoke Demonstration (Ammonium Chloride Synthesis)


White smoke produced by hydrochloric acid and ammonia
Ammonia and hydrochloric acid react to produce a white smoke of ammonium chloride. (Walkerma)

The white smoke demonstration is a simple, visually appealing chemistry project. Pour a clear liquid into a seemingly empty and watch clouds of white vapor appear. It makes a nice science magic trick and is a great introduction to a discussion of acid-base and synthesis reactions.

Materials

This is a simple reaction that only requires two chemicals:

  • Ammonia (NH3)
  • Hydrochloric acid (HCl)
  • 2 clean glass jars, about 250 mL
  • Piece of cardboard large enough to cover the jar mouth

The concentrations of the ammonia and hydrochloric acid aren’t critical, but more “smoke” results from concentrated solutions. The reaction is 1:1, so ideally aim for the same concentration for both solutions. Household ammonia and muriatic acid work, if you don’t have access to lab chemicals.

Procedure

  1. Pour a small volume of hydrochloric acid into one of the jars. Swirl it to coat the inside of the jar and return the excess to its container. Cover the jar with the piece of cardboard.
  2. Pour ammonia into the second jar. Cover it with cardboard.
  3. Invert the jar of ammonia and place it over the “empty” jar coated with HCl.
  4. When you remove the cardboard, both jars fill with smoke consisting of tiny ammonium chloride crystals.

If this cardboard method seems too complicated, simply remove the cover from the HCl-coated glass and pour a small amount of ammonia. Another way to do the white smoke demonstration is to puff ammonia vapor toward a container of hydrochloric acid.

The reaction between ammonia and hydrochloric acid produces white smoke. (Petrovskyz)

Safety

Perform this demonstration in a fume hood. Wear gloves and safety goggles. Hydrochloric acid is a strong acid, but both chemicals can cause chemical burns. The chemical reaction is exothermic, so expect heat production.

How the White Smoke Demonstration Works

Both hydrochloric acid and ammonia are water-soluble gases that exist in the vapor phase above their solutions. The reaction is a neutralization reaction between a strong acid (hydrochloric acid) and a weak base (ammonia) to produce water and a salt (ammonium chloride).

HCl + NH3 → NH4Cl

The ammonium chloride crystals are tiny, so they form smoke. (Wood smoke is a suspension of solid particles in air.) Because the crystals are heavier than air, the vapor pours like regular smoke. Eventually, the crystals settle out of air and coat the surface. The chemical reaction occurs naturally in volcanic regions and forms ammonium chloride deposits near fumaroles.

References

  • Bischof, Gustav; Paul, Benjamin H.; Drummond, J. (1854). Elements of Chemical and Physical Geology. 1. London, England: The Cavendish Society.
  • Rowley, Steven P. (2011). General Chemistry I Laboratory Manual (2nd ed.). Kendall Hunt. ISBN 978-0-7575-8942-3.
  • Wiberg, Egon; Wiberg, Nils (2001). Inorganic Chemistry (illustrated ed.). Academic Press. p. 614. ISBN 978-0-12-352651-9.

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