Higher Chemistry UNIT 2

• product of crude oil
• crude oil is fractionally distilled to separate fractions
• petrol is made by reforming the naptha fraction
• blend of hydrocarbons containing between 5 and 10 carbon atoms in their chains
• blend depends on temperature
• in summer, petrol contains fewer volatile hydrocarbons
• in winter, petrol contains more volatile hydrocarbons

• intake
• compression
• combustion
• exhaust
• when burnt, petrol produces waste gases
• under certain conditions the fuel can auto ignite- called knocking
• knocking reduces engine performance
• octane number of a fuel is its ability to resist knocking
• three ways to increase burning efficiency of petrol-
• 1- use alkanes with higher degree of branching
• 2- use aromatic hydro carbons
• 3- use cycloalkanes

• reforming alters the arrangement of atoms in molecules without necessarily changing the number of carbon atoms per molecule

•  reduce harmful exhaust emissions
• they do not use up a finite resource- naptha- which is obtained from crude oil

biofuels are fuels which come from plant or animal matter

Ethanol

• is made from sugar cane and is fermented to produce ethanol
• is renewable
• burns efficently and produces less carbon monoxide than petrol

Biogas

• mainly made up of 50-80% methane. Rest is carbon dioxide
• made form fermentation of plant and animal matter inder anaerobic conditions Bacteria act on waste materials to form biogas

its main synthesis route is by passing synthesis gas over a heated catalyst

Advantages

• burns completely- producing less soot and carbon monoxide
• less volatile than petrol

Disadvantages

• produces half the energy of petrol
• toxic
• methanol absorbs water

• can be produced by electrolysis of water
• or produced when hydrocarbons react with steam
• reduces build up of carbon dioxide in the air

Disadvantages

• hydrogen storage- is heavy in liquid or compressed form
• liquefying hydrogen is expensive
• extremely flammable

• Cn H2n + 2
• carbon to carbon single bonds
• name must end in -ane

• CnH2n
• functional group is the C=C
• name must end in -ene

• CnH2n-2
• functional group is the carbon to carbon triple bond
• name must end in -yne

• contains a hydroxyl functional group -OH
• names end in -ol

Primary Alcohol- wil have the -OH group at the end of the molecule

Secondary Alcohol- will have the -OH group in the middle of the molecule

Tertiary Alcohol- will have the -OH group in the middle of the molecule directly opposite a branch

they contain the carbonyl functional group C=O

Aldehydes

• also known as alkanals
• name will end in -al
• carbonyl always found at the end of the molecule

Ketones

• are also known as alkanones
• names end in -one
• carbonyl group will be found in the middle of the molecule

• also known as alkanoic acids
• names end in -oic acid
• have  carboxyl functional group ( COOH)
• carboxyl group at the end of the chain

• can be identified by their ester link
• are formed by the condensation reaction between an alkanoic acid and alcohol
• all ester's end in -oate
• first part of name comes from the alcohol, second part comes from the alkanoic acid.
• esters can be broken down in a hydrolysis reaction

• simplest aromatic hydrocarbon is benzene
• has formula C6H6 and has a cyclic structural formula
• each carbon atom has 4 outer electrons. 1 is spare from each carbon atom and these form an electron cloud. They are delocalised.
• These delocalised electrons make the ring very stable.
• a benzene ring where one of the hydrogen atoms has been substituted by another group is known as the phenyl group ( C6H5)

most complete form of oxidation is combustion

oxidation results in an increase in the oxygen to hydrogen ratio

Primary alcohols- are oxidised first to aldehydes and then to carboxylic acids

Secondary alcohols- are oxidised to ketones

Tertiary alcohols- can't be oxidised

Aldehydes and ketones can be returned back to their corresponding alcohols using the reducing agent, lithium aluminium hydride.

Reduction results in an increase in the oxygen to hydrogen ratio