Assume that each atom in a copper wire contributes one free electron. Estimate the number of free electrons in a copper wire having a mass of 6.4 g (take the atomic weight of copper to be 64 g mol^–1).

Given:
Atomic weight of copper = 64 g mol^-1
Mass of copper wire : m = 6.4 g
Formula used:
We know that,
Number of moles in 64 g of copper = 1
Thus, number of moles in 6.4 g of copper = 0.1
Also,
Number of atoms in one mole=N_A
Here, N_A is the Avogadro Number : N_A = 6.023× 10²³ atoms
∴No.of atoms in 0.1 mole of copper=0.1× 6.023× 10²³
∴No.of atoms in 0.1 mole of copper=0.1× 6.023× 10²²
It is given that each atom contributes one free electron,
Therefore in 0.1 mole of copper will contribute
Hence, there will be free electron in 6.4 g of copper.