Question

Assume that each of copper atom has one free electron and there is $1\, mg$ of copper. Given that atomic weight of copper $=63.5$ and Avogadro number $=6.02 \times 10^{23} .$ What is the charge possessed by these free electrons?

• A. 1.52 C
• B. 1.76 C
• C. 4.76 C
• D. 1.25 C

Answer 1

Answer: (A)

Number of atom in $1 g$ of copper,
$n=\frac{\text { Avogadro number }}{\text { atomic weight }}=\frac{6.02 \times 10^{23}}{63.5}=9.48 \times 10^{21}$
Therefore, number of atoms i.,e, number of free electrons in $1 mg$ of copper,
$n'=9.48 \times 10^{21} \times 10^{-3}=9.48 \times 10^{18}$
Charge possessed by these free electrons,
$q=n' e=9.48 \times 10^{18} \times 1.6 \times 10^{-19}=1.517 C$