Question

4.6 x 10²² molecules of a compound weigh 13.8g. If N_A = 6 x 10²³ calculate the molecular weight of this compound

Answer 1

The molecular weight of the compound can be calculated as.

• 1 mole contains an Avogadro number of molecules.N_A = 6 x 10²³ and it contains the molecular weight of the substance.

$\mathrm{No}.\mathrm{of}\mathrm{moles}=\frac{\mathrm{given}\mathrm{mass}}{\mathrm{gram}\mathrm{molecular}\mathrm{mass}}$

• The unknown number of moles in 4.6 x 10²² is

$$\begin{gathered} \mathrm{No}.\mathrm{of}\mathrm{moles}=\frac{\mathrm{no}.\mathrm{of}\mathrm{molecules}}{\mathrm{avagadro}\mathrm{number}} \\ =\frac{4.6\mathrm{x}{10}^{22}}{6\mathrm{x}{10}^{23}} \\ =0.076\mathrm{moles} \end{gathered}$$

• The molecular weight of this compound

$$\begin{gathered} \mathrm{Gram}\mathrm{molecular}\mathrm{mass}=\frac{\mathrm{given}\mathrm{mass}}{\mathrm{no}.\mathrm{of}\mathrm{moles}} \\ =\frac{13.8}{0.076} \\ =181.57\mathrm{g} \end{gathered}$$