This easy to undertake and safe experiment allows students to observe many of the features of chemical reactions as well as the three physical states of matter. This experiment clearly distinguishes a chemical change from physical change.

See the topics Chemical reactions and Physical change or chemical change? for more information.

The materials

1. Baking soda - Chemical name, sodium bicarbonate with formula NaHCO₃.
   
   
   
2. Vinegar - A dilute solution of acetic acid in water. Acetic acid is also known as ethanoic acid, with the formula CH₃COOH.
   
   
   
3. A beaker or jar.

The chemical reaction
When baking soda is mixed with vinegar, something new is formed. The mixture quickly foams up with carbon dioxide gas. If enough vinegar is used, all of the baking soda can be made to react and disappear into the vinegar solution.

The reaction is:
Sodium bicarbonate and acetic acid reacts to carbon dioxide, water and sodium acetate.

NaHCO₃ + CH₃COOH CO₂ + H₂O + Na CH₃COO

The physical changes

The solid baking soda was placed in liquid vinegar producing carbon dioxide gas, which is evident because of the formation of bubbles in the foaming mixture. Eventually all of the solid dissolved and reacted producing a new liquid solution.

During the reaction, a solid and liquid have been chemically reacted to form a gas and a liquid. This experiment can also be used to explain foams, as liquids or solids containing gas bubbles.

Safety and disposal
Although both reactants are household chemicals and foodstuffs, caution should be taken not to get splashes in the eyes and clothes should be protected. The products of the reaction are relatively safe (Remember - no chemicals should be touched) and can be disposed of by washing down the sink with plenty of water.