Home / iGCSE Chemistry 0620 Extended – 11.1 Formulae, functional groups and terminology- Exam Style Questions Paper 4

iGCSE Chemistry 0620 Extended - 11.1 Formulae, functional groups and terminology- Exam Style Questions Paper 4- New Syllabus

iGCSE Chemistry Theory (Extended) Paper 4 - All Chapters

Question

This question is about the homologous series of alkanes.
Three general characteristics of alkanes are:
  • they are generally unreactive because they do not have a functional group
  • they show trends in their physical properties, such as melting points and boiling points
  • they have similar chemical properties.
(a) Describe two other general characteristics of the homologous series of alkanes.
(b)(i) State the trend in the boiling points of the alkanes as the carbon chain length increases.
(b)(ii) Name one other physical property of alkanes that shows a trend, other than melting points and boiling points. Describe this trend as the carbon chain length of alkanes increases.
(c) State why alkanes are described as saturated.
(d) Propane has the structural formula $CH_{3}CH_{2}CH_{3}$. When propane undergoes a monosubstitution reaction with chlorine at room temperature, two organic products can be formed.
(i) State one condition needed for this substitution reaction to take place.
(ii) Give the structural formula and state the name of each organic product formed.
(iii) The two products formed are structural isomers of each other. Define the term structural isomers.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• Topic 11.4 — Alkanes
• Topic 11.1 — Formulae, functional groups and terminology

▶️ Answer/Explanation

(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).

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