C7: organic chemistry

How is crude oil formed?

• Crude oil is finite and found in rocks.

• Plankton dies, sinks to bottom of ocean and is covered in sediment

• Then compressed / compounded over millions of years and plankton turns into crude oil

What does crude oil consist of?

A mixture of hydrocarbons (hydrocarbons are molecules made of hydrogen and carbon ONLY)

What is an alkane?

• A type of hydrocarbon

• General formula C_nH_2n+2

• Single bonded and saturated

What is an alkene?

• A type of hydrocarbon

• General formula C_nH_2n

• Double covalent bond between carbon atoms and unsaturated

• Useful as they’re used to make polymers and other useful chemicals

What are the prefixes for the first 4 alkanes?

• Meth - 1 carbon atom

• Eth - 2 carbon atoms

• Prop - 3 carbon atoms

• But - 4 carbon atoms

What are the properties of hydrocarbons?

• As the size of hydrocarbons increase, the viscosity (how thick it is) increases

• As the size of hydrocarbons increase, flammability decreases

• As the size of hydrocarbons increase, boiling point increases

How can hydrocarbons be used as fuels? Also give equations.

• Hydrocarbon fuels release energy during combustion (the carbon + hydrogen are oxidised)

• Complete combustion equation: fuel + oxygen —> carbon dioxide + water

How are the hydrocarbons in crude oil separated by fractional distillation?

• Crude oil heated to vapour then put into the fractionating column (hot at bottom, cool at top)

• Hydrocarbon vapour rises + condenses when it reaches its boiling point

• The liquid fractions are then removed

• Unless they’re short chain hydrocarbons, in which case they have such low boiling points that they never condense and are removed as gases

What are the functions of important crude oil fractions?

• Petrol and diesel - car fuel

• Kerosene - plane fuel

• Heavy fuel oil - ship fuel

• Liquified petroleum gas - camping stoves

What is meant by cracking?

The process of breaking long chain alkanes into small chain alkanes and alkenes which are more useful (used for fuels etc).

What are the two types of cracking?

• Catalytic cracking - high temperature (500^oC) and catalyst used (to speed up reaction)

• Steam cracking - high temperature and steam (800^oC)

How can we test for alkenes?

They’re more reactive than alkanes. If we shake an alkene with bromine water (which is orange), the bromine water turns colourless.

How would you balance this cracking equation: C₄₀H₈₂ —> C_{_}H_{_} + C₇H₁₄

They would total to the reactant on the right, so it would be C₃₃H₆₈

Why are alkenes unsaturated molecules?

They contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms.

What is a functional group?

The part of the molecule that determines how it reacts (e.g. for alkenes it’s C=C).

Explain incomplete combustion in terms of alkenes

• Combusting an alkene follows the usual formula but also produces unburnt carbon particles due to incomplete combustion

• Alkenes burn in air with a smoky flame

How do alkenes react with hydrogen (hydrogenation)?

• Requires a temperature of around 150^oC and needs a nickel catalyst

• C=C converted to a C-C

• The two added hydrogen atoms add across the double bond

• Turns it into an alkane

How do alkenes react with water (hydration)?

• The water must be in the form of steam

• Temperature 300^oC and pressure around 70 atmospheres

• Phosphoric acid used as a catalyst

• Reversible reaction

How do alkenes react with halogens?

• C=C converted to a C-C

• The two added halogen atoms add across the double bond

What are carboxylic acids?

• Homologous series (all have the same functional group) of acids

• All have suffix ‘anoic’ and same prefixes as hydrocarbons

• General formula C_nH_2n+1COOH (always leave COOH on its own at the end - it’s the functional group)

What happens when you dissolve carboxylic acids in water?

• In water, they are weak acids so partially ionise

• Carboxylic acids have a higher pH than a strong acid

How do carboxylic acids react with carbonates?

acid + carbonate —> salt + carbon dioxide + water

How do carboxylic acids react with alcohols?

carboxylic acid + alcohol <—> ester + water

• Sulphuric acid required as a catalyst

• Reversible reaction

• If using ethanoic acid and ethanol, ethyl ethanoate (ester) is made

What are alcohols?

• Homologous series with functional group -OH

• All have suffix ‘anol’ and same prefixes as hydrocarbons

What are the main uses for alcohols?

• Fuels

• Solvents

• Alcoholic drinks

Give the formulas for the first 4 alcohols

• Methanol - CH₃OH

• Ethanol - CH₃CH₂OH

• Propanol - CH₃CH₂CH₂OH

• Butanol - CH₃CH₂CH₂CH₂OH

How is ethanol created?

• Hydration of ethene

• Fermentation of glucose (using yeast) —> ethanol (aqueous solution so needs to be purified with distillation) + carbon dioxide

  • Temperature must be around 30^oC (low so not a lot of energy required) and the reaction must take place in anaerobic conditions

  • Sugar for this reaction comes from plants (renewable)

How do alcohols react with sodium?

Sodium methoxide / ethoxide / propoxide / butoxide + hydrogen is produced

How do alcohols react with an oxidising agent?

• They produce a carboxylic acid (with same suffix) + water

• e.g. methanol —> methanoic acid + water

What happens when you add alcohols to water?

• Alcohols are soluble in water and form neutral solutions

• As the number of carbon atoms increases, the solubility decreases

What is produced when you combust an alcohol?

Carbon dioxide + water

What are the two different types of polymers?

• Addition polymers

• Condensation polymers

Explain addition polymers

• The monomers are alkenes

• For example, if it’s ethene, you produce poly(ethene)

  • The monomer contains C=C but the polymer has C-C

How would you display a repeating unit for an addition polymer?

Take two carbon atoms in the chain and add the hydrogen atoms. Then put them in brackets and add a small n to the right (represents a large number of repeating units). See below.

Explain condensation polymers

• Starts with two different monomers (which each have two of the same functional group)

• To form the polymer, react the monomers together

• Small molecules such as water are lost

• Thousands of monomers can join to make a polymer (which would then be called a polyester)

How would you display a repeating unit for a condensation polymer?

Take two adjacent monomer units in the chain. Then put them in brackets and add a small n to the right (represents a large number of repeating units). See below.

What is the structure of an amino acid?

• Has two different functional groups - amine group (H₂N) and carboxylic acid group (COOH)

How do amino acids form polypeptides and proteins?

• Two amino acid molecules can react to form as condensation polymer and water

• If the amino acids reacted together are the same, the polymer is called a polypeptide

• If the amino acids reacted together are different, the polymer is called a protein

What is the structure of DNA?

• DNA consists of two polymer chains (made from monomers called nucleotides) which wrap around eachother to form a double helix

• There are four different nucleotide monomers - G, A, T, and C

What polymers can we find in living organisms?

• Proteins —> polymers of amino acids

• Starch —> polymer of glucose

• Cellulose —> polymer of glucose