(i)

Formula mass of a compound is the sum of the atomic masses of constituent atoms in a compound.

(ii)

(i)

Mole of a substance is the amount of substance which contains same number of chemical units/atoms, molecules, etc. as there are carbon atoms in 12 g of carbon-12 isotopes.

OR

Mole of a substance is the amount of substance which contains one Avogadro number of particles.

(ii)

Method I

Using the formula

Mass of magnesium = 18 g

Molar mass = 24

Mole of magnesium metal = $\frac{18}{24}$ = 0.75 mol

Number of atoms = Mole x Avogadro number

Avogadro number = 6.023 x 10²³

Number of atoms in 18 g of magnesium metal = 0.75 x 6.023 x 10²³

Number of atoms in 18 g of magnesium metal = 4.515 x 10²³ atoms

Method II

Using proportionality

1 mole of Mg contains 6.02 x 10²³ atoms

0.75 mole of Mg contains 0.75 x 6.02 x 10²³ atoms

0.75 mole of Mg contains 4.515 x 10²³ atoms

(i)

(ii)

Differences between an element and a compound

(i)

816   O, 817    O

They both have 8 protons.

816   O has 16 - 8 = 8 neutrons

817    O has 17 - 8 = 9 neutrons

(ii)

612   C, 614    C

They both have 6 protons.

612   C has 12 - 6 = 6 neutrons

614    C has 14 - 6 = 8 neutrons

(i)

Sublimation is the process whereby solid particles change directly into the gaseous state/phase (when they obtain heat).

(ii)

Substances that can sublime

1. Iodine
2. Naphthalene
3. Camphor
4. Dry ice
5. Solid carbon dioxide/carbon (IV) oxide
6. Ammonium chloride

(i)

Relative atomic mass is the average mass of the atoms of an element compared to 1/12 the mass of a carbon-12 atom.

(ii)

Molar mass of the compounds

(α) Na₂CO₃ = (2×23) + 12 + (3×16) = 106 g/mol
(β) CH₃COOH = 12 + (4×1) + 12 + (2×16) = 60 g/mol

(i)

Number of protons and neutrons

(α) ²³₁₁Na: 11 protons
¹⁹₉F: 9 protons
(β) ²³₁₁Na: 12 neutrons
¹⁹₉F: 10 neutrons

(ii)

Electron configuration of ions

(α) Sodium ion (Na⁺): 2, 8 (positive charge shown)
(β) Fluorine ion (F⁻): 2, 8 (negative charge shown)