Question

Using the fact air is 20% O2 and 80% N2, and assuming that a standard balloon can withstand a pressure of about 1.1 atm before it bursts, show why helium and not CO2 makes good balloons.

Answer 1

The heavier molecules than air sinks in air. Lighter molecules than air floats in air.

It can be explain by using the concept of molecular weight and density of the molecules.

Calculate Molecular weight

He: 4

CO2: 12+16*2= 44

O2: 16*2=32 about 20% of air

N2: 14*2=28 about 80% of air

Air molecular weigh: O2 * 0.20 + N2 * 0.80 = 32 * 0.20 + 28 * 0.80 = 28.8

From above date its clear that CO2 is heavier than air, so it will sink in air. Helium is lighter than air so it float and makes good balloons.

We can also explain with the densities of the molecules.

The density of air: 1.3 kg/cubic meter,

                helium: 0.18 kg/cubic meter

               carbon dioxide 1.8 kg/cubic meter (at 25 degree centigrade and atmospheric pressure)