What’s in the air?

We had seen earlier that CO2 displaces air in a glass and the candle goes off. Let us see,  what happens when candle burns in air. We will do a very simple experiment. For this we need  a tall glass, a big and deep dish, some water and a mid-size candle.

Put  candle at middle of, the dish and fill the dish with water. Now light the candle and cover the flame with the glass. Now the candle burns isolated from the air outside.

After sometime, we see the candle flame goes out and some water rises inside the glass. Mark the amount of air inside the glass with a marker pen. Use a measuring cup to find ratio of air that got consumed.


1. Why did the candle go out?
2. How much air was consumed?

A Gas like water – CO2

When you open a bottle of coke, bubbles come out of the water. The gas that comes out is Carbon-di-oxide CO2. CO2 can be produced by adding some acid to lime stone, or some acid to soda/soda-bi-carb. When we burn coal or oil, then also we get Carbon-di-oxide. For our experiment, we shall use soda.

Take a spoon or two of soda in a large bottle and add some vinegar to it. Immediately lot of bobble will come out. Keep the bottle upright and in a place where there is not much wind. CO2 is heavier than air and will stay nicely in the bottle.

To check property of CO2, take two small candles light them in a glass. Now take the bottle of CO2 and tilt it like you will pour water in the glass. You will notice, the candle will extinguish as you pour CO2 in the glass.

CO2 being heavier than oxygen, displaces air/oxygen inside the glass and candle stops burning. This property is used in the fire extinguisher to stop simple fire. Also remember that same thing like candle can happen to you, if you sleep in a room without ventilator or any window.

Now let us do a test to find property of CO2. Pour some clear lime water in a test tube and then add CO2 in the test tube. Now close top of the tube with your thumb and shake the test tube. Lime water will turn turbid. This is second test. Add some Muriatic acid in the turbid lime water and it will again become clear.