Alkanes

Question 1

How does structure affect boiling point? - Alkanes

Answer 1

The boiling point of an alkane is influenced by the strength of its intermolecular induced dipole-dipole forces, which vary based on the length of the carbon chain and the extent of branching.

Question 2

General formula of alkanes?

Answer 2

CₙH₂ₙ₊₂

Question 3

Why do alkanes have low reactivity?

Answer 3

Strong C–C and C–H bonds.

Question 4

What are alkanes?

Answer 4

Saturated hydrocarbons containing only single C–C and C–H bonds. General formula: CₙH₂ₙ₊₂.

Question 5

What does “saturated” mean?

Answer 5

Contains the maximum number of hydrogen atoms; no double or triple bonds.

Question 6

What are cycloalkanes?

Answer 6

Alkanes with carbon atoms forming a ring. General formula: CₙH₂ₙ. Saturated.

Question 7

Example of a cycloalkane?

Answer 7

Cyclohexane, C₆H₁₂.

Question 8

What is the bonding in alkanes?

Answer 8

Single covalent bonds (sigma bonds) between carbon and hydrogen.

Question 9

Shape around carbon atom in alkanes?

Answer 9

Tetrahedral

Question 10

Bond angle in alkanes?

Answer 10

Approximately 109.5°

Question 11

Why tetrahedral? - Alkane

Answer 11

Four bonding electron pairs repel equally

Question 12

How does chain length affect boiling point?

Answer 12

Longer chains → more electrons → stronger induced dipole–dipole (London) forces → higher BP

Question 13

How does branching affect boiling point?

Answer 13

More branching → less efficient packing → weaker London forces → lower BP

Question 14

Compare butane and methylpropane BPs.

Answer 14

Butane (straight chain) has higher BP than methylpropane (branched)

Question 15

Purpose of fractional distillation?

Answer 15

Separates hydrocarbons based on boiling points.

Question 16

What are the steps in fractional distillation?

Answer 16

1. The mixture is vaporised and fed into the fractionating column
2. Vapours rise, cool and condense
3. Products are siphoned off for different uses

Question 17

Properties down the column - Fractional Distillation

Answer 17

Boiling point ↑, viscosity ↑, flammability ↓