Question

10 litres of oxygen and 10 litres of ${\mathrm{CO}}_2$ at the same temperature and pressure have _________ masses.

Answer 1

According to Avogadro's law, under the same conditions of temperature and pressure, equal volumes of all gases contain the same number of molecules.

Example to illustrate Avogadro's law :

If 10 L of ${\mathrm{O}}_2$at S.T.P contains n molecules of ${\mathrm{O}}_2$ then :

10 L of ${\mathrm{CO}}_2$ at S.T.P will also contain n molecules of ${\mathrm{CO}}_2$

Molar mass of ${\mathrm{CO}}_2$ = (Mass of $\mathrm{C}+2\times$Mass of $\mathrm{O}$) = $(12+2\times 16)=44g$

Molar mass of ${\mathrm{O}}_2$ = ( $2\times$Mass of $\mathrm{O}$)= $16\times 2=32g$

Mass of n molecules of ${\mathrm{O}}_2$$=44\times n$

Mass of n molecules of ${\mathrm{CO}}_2$$=32\times n$

10 litres of oxygen and 10 litres of ${\mathrm{CO}}_2$ at the same temperature and pressure have unequal masses.