organic chemistry

Hydrocarbon

Compounds that contain only carbon and hydrogen

Homologous series

A series of compounds which have the same general formula, differ by CH2 in molecular formulae from neighbouring compounds, show a gradual variation in physical properties, and have similar chemical properties

Saturated

Only contain single bonds

Why do alkanes have low melting and boiling points?

Weak intermolecular forces between molecules needs breaking so little energy required. As molecule get bigger the forces get stronger (more electrons) and melting:boiling point increases

Complete combustion of alkanes

Hydrocarbon + oxygen → carbon dioxide + water

Incomplete combustion of alkanes

Hydrocarbon + oxygen → water (soot and CO also formed)

Alkanes

CnH2n+2

Alkenes

CnH2n

Unsaturated

Contain cwrbon-carbon double bonds (C=C)

Isomers

Same molecular formula but different arrangements of atoms

Bromine reaction with alkene

Bromine water turns orange to colourless

Bromine reaction with alkane

Bromine water remains orange (no reaction)

Water reaction with alkene (hydration)

Alkene + water (steam) → alcohol

What makes a fuel good?

It burns easily, produces little ash/smoke, produces a lot of energy when burnt, is easy to store and transport

Fossil fuels example

Coal, natural gas, crude oil

Crude oil- separated by fractional distillation

• Mixture of hydrocarbons

• Collects in porous rocks underneath non porous rocks

• Pumped up from the ground and taken by pipe or tankers to oil refineries

• Includes chains eg butane and rings eg cyclohexane

• A finite source

• Used as fuels and feedstock for petrochemical industry

Fractional distillation- separation according to boiling point

• Separates crude oil into simpler more useful mixture

• Crude oil is heated strongly

• Vapour rise and condense when cool enough and then piped away

As chains get longer…

Boiling point increases so the fractions become more viscous less volatile and are harder to ignite and burn with sootier flame

Cracking

Breaks down larger less useful long chain hydrocarbons into smaller more useful alkanes (fuels) and alkenes (making polymers)

Incomplete combustion (shown by yellow flame in Bunsen burner) happen in…

• Car engines where petrol burns producing CO and spot

• Poorly ventilated rooms with coal or gas producing CO

• Faulty gas appliances if air inlet is blocked

Carbon monoxide

Tasteless, odourless, colourless toxic gas. Breathing it can cause drowsiness, coma, then death. Combines with haemoglobin in blood and stops it from carrying oxygen to cells. It poisoning advances blood transfusion is the only cure