Question

calculate the number of atom in each of the following (1) 52 moles of Ar (2) 52 u of He (3) 52 g of He.

Answer 1

(i) 1 mole of Ar = 6.022 × 1023 atoms of Ar

52 mol of Ar = 52 × 6.022 × 1023 atoms of Ar

= 3.131 × 1025 atoms of Ar



(ii) Atomic mass of He = 4amu

Or

4amu is the mass of He atoms = 1

Therefore 52 amu is the mass of He atoms= ¼*52 = 13 atoms of He



(iii) Gram atomic mass of He = 4g

Or

4g of He contains = 6.022x 1023 atoms

Therefore 52 g of He contains = 6.022x 1023 /4 * 52 = 7.83 x 1024 atoms