Organic Chemistry - Hydrocarbons and Crude oil

Hydrocarbon

Hydrocarbons are compounds that are made up of carbon and hydrogen only.

Alkanes

• saturated hydrocarbons

• this means no more hydrogen atoms can be added

• all carbon-carbon bonds are single covalent bonds

Rules for carbon and hydrogen bonding

• Carbon - Max 4 covalent bonds (can be double)

• Hydrogen - Max 1 covalent bond

General formula of an alkane

C_nH_2n+2

Homologus series

• Group of organic compounds that have similar chemical properties

• Due to them all having the same functional group

Properties of Hydrocarbons

→boiling point
→volatility
→viscosity
→flammability

What are properties of hydrocarbons dependent on?

• the size of the molecule

Boiling point

temperature at which a liquid evaporates to form a gas

Viscosity

• measure of a liquid's resistance to flow

Flammability

• how easily something will ignite

Viscosity

Measure of liquids resistance to flow

Small vs Long Hydrocarbons

Long

• High BP

• High Viscosity

• Less Volatile

• Less flamable - smoky flame

Short

• Low BP

• Flow more easily

• More volatile

• More flammable

Complete combustion of hydrocarbons

• hydrocarbon+oxygen —> carbon dioxide +water vapour (+ energy)

• plentiful supply of oxygen

• carbon and hydrogen in fuel oxidised completely

Prefixes for carbon and n0. correlation

• Meth - 1

• Eth - 2

• Prop - 3

• But - 4

• Pent - 5

• Hex - 6

Draw Alkanes Table

DRAW

Types of Formula

• Displayed

• Gernal

• Molecular

• Structural

Why are longer hydrocarbons less flammable?

• There are strong intermolecular forces between the molecules, which require more energy to overcome.

• This makes them less volatile, meaning they evaporate less easily and produce fewer flammable vapours to mix with the air.

Incomplete combustion

→ limited supply of oxygen
→ carbon monoxide and/or carbon (soot) also produced

How to test for products of complete combustion of a hydrocarbon

→ Carbon dioxide turns limewater cloudy
→ Water turns blue cobalt chloride paper pink

Crude oil

→ finite resource

—> Non renewable
→ mixture of many different carbon compounds

How was crude oil formed?

→ remains of small sea animals and plankton
→ buried in mud, layers of rock
→ subject to high pressure, temperature and absence of oxygen
→ crude oil formed under the rock due to chemically changing the organic remains

Fractional distillation process

→ heated crude oil is vaporised into a gas and enters a tall fractionating column, which is hot at the bottom and gets cooler at the top
→ vapours rise through the column
→ when hydrocarbons vapour reaches a temperature lower than their boiling point they condense into a liquid

→ liquids are led out of the column at different heights and collected in separate fractions

What are fractions of crude oil used for

→ fuels
→ feedstocks (raw materials, e.g. chemicals and plastics) by making new compounds
→ lubricants
→ construction materials (bitumen for asphalt and tar)

In terms of boiling point from lowest to highest list products of fractionating

LPG
Petrol
Kerosene
Diesel
Heavy Fuel
Bitumen

Cracking

• Process by which you break down longer hydrocarbon chains into smaller more useful hydrocarbons

• Thermal Decomposition Reaction

Why crack hydrocarbons?

→ some heavier fractions from fractional distillation of crude oil are not in high demand
→ these hydrocarbons are made up of large molecules that are difficult to vaporise and difficult to burn
→ this means that they are poor fuels
→ so are broken down into smaller, more useful hydrocarbons via cracking

Two types of cracking

→ catalytic cracking
→ thermal cracking

Catalytic cracking

→ heat fraction to form a vapour
→ pass vapour over a zeolite catalyst/ hot powdered aluminium oxide at 500 degrees

Steam cracking

→ heat fraction to form a vapour
→ mix vapour with steam at high temperature (800-900 degrees)

Product of Cracking

• Alkanes + Alkenes