Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 11.4 — Alkanes
• Topic 11.1 — Formulae, functional groups and terminology
(a)
1. They all share the same general formula of $C_{n}H_{2n+2}$.
2. Successive members differ by a $-CH_{2}-$ unit in their molecular formulas.
(b)(i) The boiling point increases as carbon chain length increases. (Due to stronger intermolecular attractive forces between larger molecules).
(b)(ii)
Property: Density (viscosity or volatility are also acceptable).
Description: Density increases as the carbon chain length increases. (If viscosity is chosen, it increases. If volatility is chosen, it decreases).
(c) Alkanes are described as saturated because all carbon-carbon bonds are single bonds, meaning no further atoms can be added to the molecule.
(d)(i) Ultraviolet (UV) light. (The energy from UV light is required to initiate the reaction by breaking the $Cl-Cl$ bond into free radicals).
(d)(ii)
Product 1 structural formula: $CH_{3}CH_{2}CH_{2}Cl$
Product 1 name: 1-chloropropane
Product 2 structural formula: $CH_{3}CHClCH_{3}$
Product 2 name: 2-chloropropane
Explanation: The chlorine atom can substitute a hydrogen on one of the end carbons (forming 1-chloropropane) or the middle carbon (forming 2-chloropropane).
(d)(iii) Structural isomers are compounds that have the same molecular formula but possess different structural formulae (their atoms are arranged and bonded in a different sequence).
