Activities | Chemistry and Biotechnology

Acid rain

Materials:

• Glass jar with lid;
• Matches;
• Phenolphthalein;
• Water;
• Sodium hydroxide (caustic soda solution) or ammonium hydroxide (ammonia solution).

Procedure :

1. Put water in the glass jar until approximately one-fifth of its height;

2. Add a few drops of phenolphthalein indicator;

3. Add a few drops of ammonia solution until the solution changes colour;

4. Light a match inside the jar and leave the match head burn away;

5. Quickly remove the match from the inside of the jar and close it;

6. Shake the jar;  

7. Observe what happens!

Explanation:

Sodium hydroxide and ammonium hydroxide are basic solutions and phenolphthalein is an acid-base indicator which turns pink in the presence of a base.  

Match boxes have on one edge a coarse striking surface that contains phosporus for lighting the matches. Contrary to what many think, matches do not contain phosphorus but the match head contains sulphur, an oxidizing agent, and glue. When we light the match, the oxidizing agent starts the burning of sulphur, which when combined with the oxygen in the air, produces sulphur dioxide.

As well as acid rain, sulphur dioxide dissolves in water, causing the medium to become acid. In acidic media the phenolphthalein is colourless.

Activity instructors: Isabel Silva, Sofia Duarte (Lab.EQ - Chemical Engineering Lab)