Question

Bell metal contains 80% copper. The mass of Bell metal which contains $1.5\times {10}^{20}$ atoms of copper is ($\mathrm{Cu}=64$)

Answer 1

• Eighty percent of the bell metal is copper-
  80 gm of copper is found in 100 gm of bell metal. Copper's molecular weight is 64 gm/mol.

$$\begin{gathered} Moles\mathit{}of\mathit{}\mathrm{Cu}=\frac{1.5\times {10}^{20}}{6.023\times {10}^{23}} \\ =0.25\times {10}^{-3} \end{gathered}$$

100 g of bell metal is included in 80 g of copper.

$$\begin{gathered} Mass\mathit{}of\mathit{}copper=64\times 0.25\times {10}^{-3}\mathrm{g} \\ 64\times 0.25\times {10}^{-3}\mathrm{g}\mathrm{of}\mathrm{Cu}contains=\frac{64\times 0.25\times {10}^3}{80}\times 100 \\ =20\mathrm{mg} \end{gathered}$$

Hence, The mass of Bell metal which contains $1.5\times {10}^{20}$ atoms of copper is 20 mg.