Chemistry through activities
Yasmin Jayathirtha
The first lesson in the chemistry class is to define what chemistry is! Students when asked what chemistry is, say; ‘reactions’ ‘acids’,’stuff in the lab’ and for some the ultimate bad word ‘chemicals’. We need to point out that we are all made up of ‘chemicals’ and the subject is the study of changes that substances undergo – as when you eat a banana and it becomes you. We also need to point out that some changes give rise to new substances and some do not – chemical and physical changes. There should be demonstrable experiments for students to decide whether a change is physical or chemical. The easiest is:
1. to heat
2. add to water
3. leave out in air.
We will try all three.
Some equipment that will be good to have are, a few hard glass test tubes, a boiling tube, a test tube holder and an alcohol thermometer (-10°–110° C). Most other equipment can be improvised.
To heat:
Heat in separate test tubes the following chemicals. The table shows what will be observed.
| Chemical | On heating | On cooling |
|---|---|---|
| iodine crystals/td> | Purple vapour | Vapour condenses on cooling |
| *Matches with heads off | Oil and vapour formed, wood chars | No further change |
| *Wax | Melts | Solidifies |
| *Zinc oxide | White powder turns yellow | Turns white again |
| Lead monoxide | Yellow powder turns orange | Turns yellow again |
| *Red lead Pb3O4 | Turns yellow and brown | No further change |
| Hydrated copper sulfate | Turns white, vapour given off, condenses | No change. If water from the top falls back turns blue |
| Copper carbonate | Green powder turns black | No further change |
To add to water:
| Chemical | On adding | after evaporation |
|---|---|---|
| *Sugar/td> | Dissolves | Sugar crystallises out |
| *Salt | Dissolves | Salt crystallises out |
| *Hydrated copper sulfate | Dissolves to give blue solution | Blue crystals |
| Small piece of sodium metal | Fizzes about and disappears | White solid |
| *Copper sulfate white | Dissolves to give blue solution | Blue crystals |
| Piece of magnesium ribbon | Bubbles form on surface. Disappears after about a week | White solid |
| *Baking powder | Fizzes and disappears | White solid |
To leave out in air:
| Chemical | On exposure to air |
|---|---|
| *An iron nail | Rusts |
| *Copper wire (remove insulation) | Gets a black coating |
| Sodium hydroxide pellets | Absorbs water and forms a solution |
| *Copper sulfate (white) | Absorbs water and turns blue |
| Sodium metal | Dulls and gets a white/yellow coating |
| *Cut piece of apple/brinjal | Turns brown |
For those who do not have lab facilities, Iodine, lead monoxide, copper carbonate, sodium metal, magnesium ribbon and sodium hydroxide will be hard to get. They can be purchased from chemical supply stores, of course, but the expense may not be worth it. Iodine is very expensive and definitely not worth it, the others are more affordable and will last a long time so you will have to decide. A fairly clear picture can be got from using the substances marked with an asterisk*. Copper sulfate can be bought in hardware stores, zinc oxide from pharmacies and red lead is sindhoor. The reasons for buying them from these sources rather than chemical supply stores are: a) you can buy smaller quantities and b) they are likely to be cheaper. We can purify them and that will also be a learning experience.
As you can see from the pictures, spoons make perfectly adequate spatulas! Make sure that chemicals are not spilt near food if you are using the gas stove for heating.
Always wash hands thoroughly.
The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.
