Calculate the number of moles present in: (i) 3.011 x 1023 number of oxygen atoms. (ii) 60 g of calcium [Given that atomic mass of Ca = 40 u, Avogadro No. = 6.022 × 1023]

(i) 1 mole of oxygen contains 6.022 x 10²³ atoms

  ∴ 6.022 x 10²³ atoms of oxygen = 1 mol

1 atom of oxygen = 1 / 6.022 × 10²³ mol

 ∴ 3.01 1 x 10²³ atoms of oxygen = (1 × 3.011 × 10²³) / (6.022 × 10²³) mol

                                                        = 0.5 mol

(ii) Atomic mass of Ca = 40 u

40g of calcium = 1 mol

60g of calcium = 60/40 mol

= 1.5 mol