Sour candy chemistry

Add candies to a baking soda solution, to confirm or predict which ones are the sour and regular candies.
Science content
Biology: Sensing, Organ Systems (4, 5, 6)
Chemistry: States of Matter, Properties of Materials (K-7)
Chemistry: Atoms, Molecules (3-7)
Chemistry: Chemical Changes (2, 7)
Lessons activity is in
  • candies of the same brand, some sour, some regular - skittles work well (note: some sour candies have visible acid crystals on the outside, some do not)
  • tray with wells e.g. paint tray or ice cube tray
  • baking soda
  • small scoop or coffee stir stick
  • water in a squeeze bottle

Depending on the manufacturing of sour candies, distribute candies in this way:
If the sour candies have visible white acid crystals on the outside (but the regular skittles do not), whole candies should be distributed to students.
If the sour candies have the same appearance (apart from colour) to the regular candies, cut candies in half before distributing to students.

Students use the coffee stir stick to add a small scoop of baking soda to a few wells of the tray. Squirt water into the wells to dissolve the baking soda and make a concentrated baking soda solution.
If a sour candy has a coating of acid crystals:
Distribute candies to the students so that they can add the whole candy to each well of the tray. As the sour candies have a coating of visible white acid crystals, students will confirm that sour candies behave differently in baking soda solution from regular candies. They should see that the sour candies make bubbles when added to the baking soda solution, whereas the regular candies do not. The sour candies have an acid added to their coating, which chemically reacts with the baking soda to produce bubbles of gas.
If a sour candy looks identical (apart from colour) to regular candies:
Give students half candies to test. Give them sour and regular candy-halves and ask them which make bubbles when added to the baking soda solution in their own wells of the tray (wait a few minutes before comparing). The candy halves that continuously make bubbles are the sour candies. The candy halves that maybe make a few bubbles but the stop are the regular candies. Ask students to predict which are sour candies and which are regular. Confirm by reading the packet - (although some students will already be familiar with the candy and know already!)

If appropriate, discuss the chemical reaction:
The baking soda (HCO2) reacts with the H atoms of the sour candy coating/inside to make carbon dioxide (CO2) gas.
Students can use molecular models to figure out the reaction: give them the starting molecules, ask them to make water (H2O) and figure out what other molecule is made. When they use up all the atoms and bonds, and fill all the holes on the atoms, they should arrive at CO2, which is a gas, and makes the bubbles that they see.

Grades taught
Gr 4
Gr 5
Gr 6
Gr 7