Question

(i) Define mole. What are the two things that a mole represents?
​(ii) What weight of each element is present 1.5 moles of sodium sulphite, Na₂SO₃? (Atomic masses: Na = 23u; S = 32 u; O = 16 u.)

Answer 1

(i) A mole is a unit of measurement used to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon 12.
A mole represents:
a) One mole of any substance contains 6.022$\times$10²³ particles. This means that one-mole atom, molecule or ions of any substance contain 6.022$\times$10²³ atoms.
b) One mole of a substance is that quantity in number having a mass equal to its atomic or molecular mass in grams.

(ii)
For 1 mole of sodium sulphite, Na₂SO₃
The atomic mass of sodium, Na = 23 g
for 2 atoms of sodium, the atomic mass of sodium = 2×23 g
= 46 g
The atomic mass of sulphur, S = 32 g
The atomic mass of oxygen, O = 16 g
for 3 atoms of oxygen, the atomic mass of oxygen = 3×16 g
​ = 48 g
For 1.5 mole of sodium sulphite, Na₂SO₃, the weight of each element is,
For sodium, weight = 1.5×46 g
= 69 g
For sulphur, weight = 1.5×32 g
= 48 g
For oxygen, weight = 1.5×48 g
= 72 g