Question

estimate the number of molecules in 3.00m^3 of air by assuming that it has a density of 1.21kg/m^3 and that is entirely composed of nitrogen molecules

Answer 1

Total volume of the gas=3.0$m^3$

Density of the molecule =$1.21 kg/m^3$

we know that the atomic weight of the nitrogen molecule=$28.014 gm/mol$

We know that,

mass = density x volume

$m= 3\times 1.21 kg$

$m=3.63kg$

Hence the number moles=$\dfrac{3.63\times 1000}{28.014}=129$ .578

We know that the avagadro number (number of molecules per mole)=$6.023\times 10^{23}$

Hence the number of nitrogen molecules $=129.578\times 6.023\times 10^{23}=780.45\times 10^{23}$ molecules.