Organic Chemistry

Question 1

What is a hydrocarbon

Answer 1

A compound made of only carbon and hydrogen atoms.

Question 2

What are alkanes

Answer 2

• Saturated hydrocarbons (only single bonds).
• General formula: CₙH₂ₙ₊₂.
• Example: Methane (CH₄), Ethane (C₂H₆).

Question 3

What are alkenes

Answer 3

• Unsaturated hydrocarbons (contain at least one double bond).
• General formula: CₙH₂ₙ.
• Example: Ethene (C₂H₄), Propene (C₃H₆).

Question 4

What is crude oil

Answer 4

A mixture of hydrocarbons, mainly alkanes, formed from ancient biomass over millions of years.

Question 5

Why is Bitumen Not Used as a Fuel

Answer 5

• High boiling point
• Low volatility
• High viscosity

Question 6

How is crude oil separated

Answer 6

Fractional distillation heats crude oil to evaporate the hydrocarbons. The vapour is fed into a fractioning column which is coolest at the top and hottest at the bottom. This results in a temperature gradient in the column. Vapour moves up the Column and starts to cool down. When it cools down it condenses and turns into a liquid. Different fractions condense at different levels in the column depending on their boiling points. If a fraction has a low boiling point it will condense toward the top of the column. If it has a high boiling point it will condense toward the bottom of the column.

Question 7

What are the fractions of crude oil used for

Answer 7

• Refinery gases → LPG (bottled gas).
• Petrol → Car fuel.
• Kerosene → Aircraft fuel.
• Diesel → Fuel for cars and trucks.
• Bitumen → Roads and roofing.

Question 8

What is cracking

Answer 8

• Catalytic cracking → Uses a hot catalyst at high temperature.
• Steam cracking → Uses high temperature and steam to break hydrocarbons.

Question 9

What is combustion

Answer 9

Burning fuels to release energy.
• Complete combustion (plenty of oxygen):
Hydrocarbon + O₂ → CO₂ + H₂O
• Incomplete combustion (limited oxygen):
Hydrocarbon + O₂ → CO + H₂O (Produces toxic carbon monoxide).

Question 10

How do alkenes react with bromine water

Answer 10

Alkenes decolourise bromine water from orange → colourless (test for alkenes).

Question 11

What are alcohols

Answer 11

• Contain -OH (hydroxyl) group.
• General formula: CₙH₂ₙ₊₁OH.• Example: Ethanol (C₂H₅OH).
• Used in drinks, fuels, and solvents.

Question 12

What are polymers

Answer 12

• Long-chain molecules made from monomers.
• Addition polymerisation → Alkenes join together.
• Example: Poly(ethene) from ethene.

Question 13

Which hydrocarbon molecule can be cracked to produce octane (C₈H₁₈)

Answer 13

Dodecane (C₁₂H₂₆)

Question 14

What are two conditions used for cracking

Answer 14

1. High Temperature (typically 450–900°C)
2. Catalyst or Steam
   • Catalytic Cracking: Uses a hot catalyst (e.g., zeolite) to speed up the reaction.
   • Steam Cracking: Uses high temperature + steam to break hydrocarbons.

Question 16

Ethane vs. Ethene

Answer 16

Structure & Bonding:
• Ethane (C₂H₆): Single C-C bond, each carbon forms 4 single bonds.
• Ethene (C₂H₄): Double C=C bond, each carbon forms 2 single bonds.

Reactions:
• Ethane: Undergoes substitution reactions (e.g., reacts with bromine in UV light).
• Ethene: Undergoes addition reactions (e.g., decolorizes bromine water, reacts with hydrogen or steam).