Question

The density of copper is $9\times 10^{3}kg/m^3$ and its atomic mass is $63.5u$ . Each copper atom provides one free electron. Estimate the number of free electrons per cubic metre in copper,

• A. $10^{19}$
• B. $10^{23}$
• C. $10^{25}$
• D. $10^{29}$

Answer 1

Answer: (D)

Density of copper,
$\rho =9\times 10^{3}kg/m^3$
$=9\times 10^{6}g/m^3$
Avogadro number, $N_A=6.023\times 10^{23}$
Mass of $1$ mole of copper atom, $M=63.5g$
Thus, number of free electrons per volume is
$n=\frac{N_A}{M}\rho =\frac{6.023\times 10^{23}}{63.5}\times 9\times 10^6$
$=8.5\times 10^{28}{m}^{-3}$