How to Do the White Smoke Chemistry Demonstration

Reaction of hydrochloric acid and ammonia

The chemical reaction between hydrochloric acid and ammonia produces a white smoke.
The chemical reaction between hydrochloric acid and ammonia produces a white smoke consisting of ammonium chloride vapor. Walkerma, Wikipedia Commons

React a jar of liquid and an apparently empty jar to make smoke. The white smoke chemistry demonstration is easy to perform and visually appealing.

Difficulty: Easy

Time Required: Minutes

What You Need

Hydrochloric acid and ammonia are aqueous solutions. The concentrations of these chemicals is not critical, but you'll get more "smoke" with concentrated solutions because there will be more vapor. Ideally, go for solutions of the same concentration (again, not critical).

  • Ammonia (NH3)
  • Hydrochloric Acid (HCl)
  • 2 clean glass jars, both the same size, about 250 ml
  • Square of cardboard large enough to cover the mouth of the jar

Here's How

  1. Pour a small volume of hydrochloric acid into one of the jars. Swirl it around to coat the jar, and pour the excess back into its container. Place a square of cardboard over the jar to cover it.
  2. Fill the second jar with ammonia. Cover it with the square of cardboard, which will now be separating the contents of the two containers.
  3. Invert the jars, so the ammonia is on top and the apparently empty jar is on the bottom.
  4. Hold the jars together and pull the cardboard away. Both jars should immediately fill with a cloud or 'smoke' of tiny ammonium chloride crystals.

Tips

Wear gloves and safety goggles and perform the demonstration in a fume hood. Both ammonia and hydrochloric acid can give nasty chemical burns. The reaction is exothermic, so expect some heat to be produced. As always, observe safe lab procedure.

How It Works

Hydrochloric acid is a strong acid, while ammonia is a weak base. Both are water soluble gases that exist in the vapor phase above their solutions. When the solutions mix, the acid and base react to form ammonium chloride (a salt) and water in a classic neutralization reaction. In the vapor phase, the acid and base simply combine to form an ionic solid. The chemical equation is:

HCl + NH3 → NH4Cl

The ammonium chloride crystals are very fine, so the vapor looks like smoke. The crystals suspended in air are heavier than regular air, so the reacted vapor actually pours like smoke. Eventually, the tiny crystals settle onto the surface.