more dates coming soon!

Fizzy Sherbet

Are you having a spoon full of sugar and still not getting enough of a thrill? Never fear! This clever science trick will have you dancing on the roof tops.

Australian Curriculum links

  • Science > Science Inquiry Skills > Foundation > ACSIS011
  • Science > Science as a Human Endeavour > Foundation > ACSHE013
  • Science > Chemical Sciences > Year 2 > ACSSU031
  • Science > Chemical Sciences > Year 6 > ACSSU095
  • Science > Chemical Sciences > Year 8 > ACSSU225
  • Science > Chemical Sciences > Year 9 > ACSSU179

You'll need

  • Icing sugar
  • Sodium bicarbonate (baking soda)
  • Powdered citric acid (from the health food section in your supermarket)
  • Plastic cup or patty pans
  • Teaspoon
  • Tablespoon

Try this

  1. Add one tablespoon of icing sugar, one teaspoon of bicarbonate of soda and one teaspoon of citric acid to the plastic cup.
  2. Stir thoroughly.
  3. Take a small amount of the mixture using a clean teaspoon and put it in your mouth.
  4. Feel what's happening on your tongue.
  5. Repeat steps three and four.

Further investigation

Try adding different amounts of each ingredient to see if you can make the mixture more or less fizzy. Be careful not to add too much citric acid, or your sherbet will taste very sour.

You could also try adding your sherbet to different sweet recipes (like cookies, cakes or ice cream). See if you can keep it from fizzing until the sherbet is in your mouth!

What's happening?

The fizzing on your tongue is caused by a chemical reaction between the citric acid and the sodium bicarbonate. When the citric acid and sodium bicarbonate touch your saliva, they react together to make bubbles that fizz and pop in your mouth. The icing sugar makes the mixture taste nice.

This reaction is similar to the more common reaction between vinegar and sodium bicarbonate. When an acid (like vinegar or citric acid) is mixed with a carbonate (like sodium bicarbonate), they react to form carbon dioxide gas, water and a salt. The carbon dioxide produced in this reaction is what makes the bubbles on your tongue.

Reactions between citric acid and sodium bicarbonate take a very, very long time if both chemicals are in the form of a solid powder. If they are dissolved in water, however, the reaction will go significantly faster. That is why no bubbles of carbon dioxide are formed until you wet the chemicals with your saliva. Household vinegar has a lot of water in it already, so reactions with vinegar and sodium bicarbonate happen very quickly and don't require additional water.

We can write the acid/carbonate reaction as a chemical equation:
Acid + Carbonate --› Carbon Dioxide + Water + Salt

For vinegar and sodium bicarbonate, the chemical equation is:
Vinegar + Sodium Bicarbonate --› Carbon Dioxide + Water + Sodium Acetate
CH3COOH + NaHCO3 --› CO2 + H2O + CH3COONa

For citric acid and sodium bicarbonate, the chemical reaction reads:
Citric Acid + Sodium Bicarbonate --› Carbon Dioxide + Water + Sodium Citrate
C6H8O7 + 3NaHCO3 --› 3CO2 + 3H2O + C6H5O7Na3

Real world links

The break down of citric acid into carbon dioxide is happening right now inside your body (whether you've just had some sherbet or not). It is part of a very important biological process called the tricarboxylic acid cycle (TCA cycle) or the Krebs cycle, which is vital for helping turn the fuel in our bodies into energy.