1. calculate the no. of aluminium ions present in 0.051 gms of aluminium oxide( at.mass =27 unit).

2. calculate the mass of 1 mole of nitrogen.

3.10 moles of sodium sulphite. calculate the mass.

a.

Mass of 1 mole Al₂O₃ = 102 g.

102 g Al₂O₃ = 1 mol

0.051 g Al₂O₃ = (1/102 ) x 0.051 =  5 x 10^-4 mol.

Number of Al₂O₃ molecules  in  5 x 10^-4 mole = (6.032 x 10²³)x( 5 x 10^-4) = 3.0115 x 10²⁰

Number of aluminum ions per molecule = 2.

Number of aluminum ions in mole Al₂O₃ =3.0115 x 10²⁰ x 2 =6.023 x 10²⁰

b^.

Mass of 1 mole of nitrogen(N₂) = molar molecular mass of nitrogen = 14 g

C.

Mass of 10 mole of sodium sulphide = 10 x molecular mass of sodium sulphite

= 10 x 126 = 1260 g