Ammonia and hydrochloric acid

Carlos Corrêa, at the Faculdade de Ciências, Universidade do Porto, Portugal, sent in this photo capturing the acid-base reaction between ammonia and hydrochloric acid. Inside the bottle it is the vapours of the acid and the base that react. The product is ammonium chloride, which is a solid and appears as white smoke. Have your students write out the chemical reaction — don’t forget to include the states of matter — and have them find the heat of reaction. Another challenge would be to have your students explain the pathway of the smoke — the fine particles of NH₄Cl — as it appears to float out of the bottle, and then begins to track downwards. A lot of chemistry is captured in this simple photo.