Topic 4: States of Matter

Question 1

Definitions I:
(a) Ideal gas
(b) Giant ionic structure
(c) Simple molecular structure

Answer 1

Definitions I:
(a) Gas with zero particle volume and no intermolecular forces.
(b) 3D lattice of oppositely charged ions, e.g., NaCl.
(c) Discrete molecules held by weak intermolecular forces, e.g., I₂.

Question 2

Definitions II:
(a) Giant molecular structure
(b) Giant metallic structure
(c) Pressure (gas)

Answer 2

Definitions II:
(a) 3D network of atoms covalently bonded, e.g., diamond.
(b) Lattice of positive metal ions with delocalised electrons, e.g., Cu.
(c) Force exerted by gas molecule collisions on container walls.

Question 3

What causes gas pressure, and how does it differ in real vs. ideal gases? [3 Marks]

Answer 3

Collisions of molecules with walls cause pressure (1 mark)
Ideal: no forces, zero volume (1 mark)
Real: has forces, volume (1 mark)

Question 4

Calculate the volume of 2 mol CO₂ at 300 K and 100 kPa using pV = nRT. [2 Marks]

Answer 4

V = nRT/p, V = (2 × 8.31 × 300) / 100000 (1 mark)
V = 0.04986 m³ = 49.86 dm³ (1 mark)

Question 5

Describe the bonding and structure of:
(a) NaCl [1 Mark]
(b) I₂ [1 Mark]

Answer 5

(a) Ionic lattice, Na⁺ and Cl⁻ alternate (1 mark)
(b) Covalent I₂ molecules, weak van der Waals’ between (1 mark)

Question 6

What properties distinguish graphite from diamond? [3 Marks]

Answer 6

Graphite: layers, delocalised electrons, conducts (1 mark)
Diamond: tetrahedral, no free electrons, insulator (1 mark)
Different C-C bonding structures (1 mark)

Question 7

Why does MgO have a higher melting point than NaCl? [2 Marks]

Answer 7

Mg²⁺ and O²⁻, stronger ionic attraction (1 mark)
Na⁺ and Cl⁻, weaker lattice energy (1 mark)

Question 8

How does ice’s structure affect its density compared to water? [2 Marks]

Answer 8

Open H-bonded lattice in ice, less dense (1 mark)
Collapses in liquid, higher density (1 mark)

Question 8

What type of structure and bonding is in:
(a) SiO₂? [1 Mark]
(b) Cu? [1 Mark]

Answer 8

(a) Giant molecular, covalent network (1 mark)
(b) Giant metallic, delocalised electrons (1 mark)

Question 9

Calculate Mᵣ of a gas if 0.5 mol occupies 12 dm³ at 25°C and 100 kPa. [2 Marks]

Answer 9

nRT = pV, Mᵣ = mass/(pV/RT) (1 mark)
Mᵣ = 0.5 × 0.012 × 100000 / (8.31 × 298) = 24.2 (1 mark)

Question 10

Why does I₂ have a low melting point and no conductivity? [2 Marks]

Answer 10

Weak van der Waals’ between I₂ molecules (1 mark)
No free electrons or ions to conduct (1 mark)

Question 11

Predict the solubility of C₆₀ in water based on its structure. [2 Marks]

Answer 11

C₆₀ simple molecular, non-polar (1 mark)
Insoluble in polar water (1 mark)