Question

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

Answer 1

Answer:

mole is amount of substance that contains the same number of particles as there are atoms in exactly 12 gram of carbon 12

Answer 2

Mass of Sodium Sulphite is 189

Explanation:

A mole represents two things:

1. It represents a definite amount of the substance i.e. an amount of substance equal to its gram atomic mass or gram molecular mass.

2. It represents a definite number ($6.022 \times 10^2^3$) of atoms, molecules or ions of a substance

Mole: The 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 (e.g., atoms, molecules, ions, electrons) as there are atoms in 12 grams of pure carbon-12 (12C), the isotope of carbon with atomic weight 12.

• b.) Sodium sulphite $(Na_2SO_3)$

No.of moles= $\frac {mass}{molar\ mass}$

1.5 = $\frac {mass}{126}$

Mass = $126 \times 1.5$ = 189 answer this will be total mass

Now to calculate mass of each element u can simply apply mole concept here

• For $Na_2$

No.of moles = $\frac {mass}{molar\ mass}$

1.5 = $\frac {mass}{46}$

Mass = $46 \times 1.5$

= 69

• For sulphur

1.5= $\frac {mass}{32}$

Mass =48

• For $O_3$

1.5 = $\frac {mass}{48}$

Mass= 72