Question

Calculate the number of atoms in 6.00 g of calcium.

Answer 1

The number of atoms in one mole of calcium equals the Avogadro's number $N_A$ : 6.022·10²³ mol^-1. The number of the moles of calcium $n$ is its mass $m$ divided by its molar mass $M = 40.08\text{ g/mol}$ :

$n = \frac{m}{M} = \frac{6.00\text{ g}}{40.08 \text{ g/mol}} = 0.1497$ mol.

Therefore, the number of atoms of calcium is:

$N = n·N_A = 0.1497·6.022·10^{23} = 9.01·10^{22}$ .

Answer: the number of atoms in 6.00 g of calcium is 9.01·10²².