Question

What is the mass of carbon dioxide which contains the same number of molecules as are contained in $40\, g$ of oxygen?

• A. $40\,g$
• B. $55\,g$
• C. $32\,g$
• D. $44\,g$

Answer 1

Answer: (B)

Molar mass of $O_{2} = 32\, g\, mol^{-1}$
$ 32\, g\,$ of $ \,O_{2} = 6.023 \times 10^{23}$ molecules
$40 \,g$ of $O_{2}=\frac{ 6.023\times10^{23} \times40}{32} $
$ = 7.529\times10^{23} $ molecules
Mass of $6.023\times10^{23}$ molecules of $CO_{2} = 44\,g$
Mass of $7.529 \times 10^{23} $ molecules of $CO_{2}$
$ = \frac{44\times7.529\times10^{23}}{6.023\times10^{23}} = 55g$