First of all we must remember that the food colouring and detergent have nothing to do with the ‘chemical change’ which is taking place. They simply add to the effect and make things easier to see!
What is bicarbonate of soda?
The proper chemical name is Sodium Hydrogen Carbonate
The chemical formula describing exactly what it contains is NaHCO3
The formula tells us that each individual particle (molecule or ‘formula unit’) of bicarbonate of soda contains
1 atom of Sodium Na
1 atom of Hydrogen H
1 atom of Carbon C
3 atoms of Oxygen O
All of these atoms are stuck together or ‘bonded’ and there are a number of ways we can make them split apart and change their appearance or change them for good into something different.
1. Add water
When water is added and the mixture is stirred the bicarbonate of soda starts to split apart and divide itself evenly in the water. We call this ‘dissolving’. The amount of solid bicarbonate of soda gets less and less until eventually we can’t see it any more. The bicarbonate of soda is still there but no longer as solid particles. It is completely and evenly spread out in the water. If the water was allowed to dry up or ‘evaporate’ we would get back all of the white solid bicarbonate of soda that we started with. Dissolving something doesn’t change it into something new although it does look like it may have. Dissolving can be reversed by taking away the water so it is not a permanent change. It is a reversible change.
If we heat solid bicarbonate of soda strongly enough it starts to produce carbon dioxide gas and water. These are lost into the air so the bicarbonate starts to loses mass. We could check this using some weighing scales. This is a permanent change and it can’t be reversed. The carbon dioxide and water have resulted from the breaking up or decomposition of the bicarbonate of soda molecules. Something new has been formed from the original material. The white solid left behind looks the same as the original sodium Hydrogen carbonate but in actual fact it is a new substance called sodium carbonate.
3. Adding an acid such as vinegar
When vinegar is added to bicarbonate of soda a vigorous ‘reaction’ takes place. The two substances together combine then rearrange to make 3 new substances which can’t be converted back into their original form. As with heating, the newly formed substances include carbon dioxide gas and water. In addition to this a new substance which is part ‘soda’ and part vinegar is made and it is called sodium acetate. The ‘acetate’ part of the name comes from the vinegar which has a proper chemical name of ‘acetic acid’.
When the acid and bicarbonate combine an irreversible change takes place. The final product is no longer an acid and the carbon dioxide which is produced as bubbles of gas is lost to the air. Again there is a weight loss as with heating and this is s sure sign of a permanent or irreversible change.