Question

How many atoms are in 115 g of calcium?

Answer 1

First find the number of moles of calcium we have,

No. of moles = Given mass / Molar mass

Mass of calcium given = 115 g

Molar mass of calcium = 40 g

So,

No. of moles of calcium = 115 / 40 = 2.875 mol

As we know,

No. of atoms in 1 mole of any element = 6.022 * 10²³   (Avogadro number)

Thus, No. of atoms in 1 mole of calcium = 6.022 * 10²³

No. of atoms in 2.875 moles of calcium = 2.875 * (6.022 * 10²³) = 1.731 * 10²⁴

Thus, 115 g of calcium has 1.731 * 10²⁴ atoms .