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.