4.7 Organic chemistry

What’s an organic compound?

A compound that contains at least one Carbon atom - typically bonded to hydrogen and sometimes oxygen.

What is crude oil?

Crude oil is a finite resource found in rocks.

How was crude oil formed?

It is the remains of ancient biomass consisting mainly of plankton that was buried under mud.

What is crude oil made up of?

Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons. Most of the hydrocarbons in crude oil are alkanes.

What is a hydrocarbon?

A molecule made up of carbon and hydrogen atoms only

What are most of the hydrocarbons in crude oil?

Alkanes

What is a homogolous series?

A group of organic compounds with the same functional group

What is meant by ‘functional group’

A functional group is a specific group of atoms in a molecule that is responsible for its chemical properties and reactivity characteristics

What is the general formula for the homogolous series of alkanes?

C_nH_2n+2

What are the first four members of the alkanes?

Methane, ethane, propane, butane

What are alkanes?

Alkanes are a type of hydrocarbon.

They are saturated hydrocarbons as they only have single covalent bonds.

What is the general formula for alkanes?

C_nH_2n+2

What is the process by which the many compounds of crude oil can be separated?

Fractional distillation

Why is crude oil separated?

To produce fractions of different hydrocarbons

Different hydrocarbons have different uses, so separating them allows them to be used for their specific uses.

Describe fractional distillation of crude oil

Purpose: to seperate crude oil into fractions based on boiling point

• Crude oil is heated until it vaporises (this breaks the intermolecular forces between hydrocarbons)

• The vapour enters the fractionating column which is cooler at the bottom and hotter at the top

• Long chain hydrocarbons with high boiling points condense nearer to the bottom where it is cooler

• Short chain hydrocarbons with low boiling points condense nearer to the top where it is hotter

• Different fractions are collected at different levels of the column

• Each fraction has hydrocarbons with similar chain lengths and boiling points

What do the different fractions of fractionally distillated crude oil contain?

Molecules with similar number of carbon atoms (chain length and boiling point).

This is because molecules with a larger amount of carbon atoms (longer chains) have lower boiling points so condense together at lower fractions, whereas molecules with a smaller number of carbon atoms (shorter chains) have higher boiling points so condense together at higher fractions.

What determines the properties of hydrocarbons?

• Size of the molecule (chain length)

• Types of bonds (whether its saturated or unsaturated)

Define feedstock

A raw material used in an industrial process to create a new product

What is the petrochemical industry?

The industry that uses fractions of crude oil to make useful chemicals and products.

Describe the uses of the fractions of crude oil

They can be processed to produce fuels and feedstock for the petrochemical industry.

Many of the fuels which we depend on are produced from crude oil:

• petrol

• diesel oil

• kerosene

• heavy fuel oil

• liquefied petroleum gases

Many useful materials which we depend on are produced by the petrochemical industry:

• solvents

• lubricants

• polymers

• detergents

Why is there a vast array of natural and synthetic carbon compounds?

Because it can form families of similar compounds.

This is possible because carbon can form chains and rings linked by covalent carbon-carbon bonds.

How does boiling point, viscosity and flammability change with increasing molecular size of hydrocarbons and why?

As the hydrogen carbon chain increases, and the molecule gets larger:

• boiling point increases

Bigger molecules have stronger intermolecular forces, so more energy (heat) is needed to seperate them

• viscosity increases

Longer molecules get tangled and flow less easily as they get stuck going past eachother, making them thicker

• flammability

less flammable, hider to ignite. This is because to burn, a fuel must be in a gaseous state, so as their boiling point is higher, they don’t evaporate into vapour as easy, so therefore don’t burn easily.

What is combustion in general?

An exothermic reaction where a fuel reacts with oxygen to release energy.

It can be complete (if there is enough oxygen) or incomplete (if there is limited oxygen).

Describe complete combustion of hydrocarbons

Combustion is the chemical reaction where a fuel reacts with oxygen to release energy.

Complete combustion occurs when there is enough oxygen.

Hydrocarbon + oxygen → carbon dioxide + water

A lot of energy is released (more than incomplete combustion) (as more bonds are formed (more carbon-oxygen bonds are formed as all the carbon forms carbon dioxide) which releases energy).

Features: clean flame, no soot

This is because in complete combustion there is enough oxygen for the hydrocarbon to react fully and all of the carbon to form carbon dioxide, therefore no solid carbon (soot) is formed, meaning that the flame is also clean.

Describe incomplete combustion of hydrocarbons

Combustion is the chemical reaction where a fuel reacts with oxygen to release energy.

Incomplete combustion occurs when there is limited oxygen.

Hydrocarbon + oxygen → carbon monoxide + carbon (soot) + water

Less energy is released compared to complete combustion, as less bonds are formed (which releases energy) as not all the carbon forms carbon-oxygen bonds.

Features: smoky flame, soot
In incomplete combustion there is limited oxygen, so not all of the carbon atoms form carbon dioxide; some form carbon monoxide and some remain as carbon (soot). Soot causes a smoky flame.

Write a word equation and a balanced equation for complete combustion of a hydrocarbon

Hydrocarbon + oxygen → carbon dioxide + water

How can hydrocarbons be made into more useful molecules?

By breaking them down (cracking them) into smaller molecules

Describe the two methods of breaking hydrocarbons down into smaller molecules

Steam cracking:

• The hydrocarbon is vaporised and mixed with steam at very high temperatures

• This causes thermal decomposition to occur, so it is broken down into smaller molcules

Catalytic cracking:

• Vaporised and passed over a very hot catalyst

• This weakens the hydrocarbons’ bonds and allows them to break down into smaller molecules

What are the products of cracking?

Alkanes and alkenes

What are alkenes?

Alkenes are a type of hydrocarbon.
They are unsaturated hydrocarbons as they have at least one carbon-carbon double bond.

Why are alkene molecules described to be unsaturated?

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

What is the general formula for alkenes

C_nH_2n

What is more reactive alkanes or alkenes and why?

Alkenes are more reactive.

This is because the carbon-carbon double bond is weaker, so it breaks and allows it to react more easily.

How to test if a substance is an alkene or alkane?

Add the substance to bromine water (which is orange).

If an alkene is present, the bromine will go from orange to colourless as the carbon-carbon double bond reacts with bromine.

If alkane is present the bromine water will remain orange as no reaction occurs as they are less reactive (as they don’t have this C-C double bond).

What are the uses of smaller hydrocarbons from cracking and why?

Used as fuels

This is because they have lower boiling points, so vaporise more easily to mix with oxygen (for combustion) and make combustion more efficient as this also makes them more flammable.

Give uses of alkenes

• Make polymers

• Chemical feedstock to make other chemicals

Give examples to explain the usefulness of cracking

• Make alkenes for chemical feedstock and polymers

• Making more efficient fuels and petrol

What are the first four molecules of the homogolous series of alkenes?

Ethene, propene, butene and pentene

Cannot be methene as methene only has one carbon atom and an alkene needs at least two carbon atoms to form a carbon-carbon bond.

What is the functional group of alkenes?

C=C

Generally, what determines the reactions of organic compounds?

Functional groups

How do alkenes react with oxygen?

They react with oxygen in the same way as other hydrocarbons, but they tend to burn in air with smoky flames due to incomplete combustion.

In air they combust incompletely as they have a higher proportion of carbon to hydrogen than alkanes and therefore require a very large amount of oxygen that is not supplied in air.

Complete:

alkene + oxygen → carbon dioxide + water

Incomplete:

alkene + oxygen → carbon monoxide + carbon + water

Do alkenes combust completely or incompletely in air and why?

Incompletely.

They need very large amounts of oxygen to combust completely as they have a higher proportion of carbon to hydrogen compared to alkanes. There is not enough oxygen in air for this.

What substances do alkenes react with?

• Oxygen

• Hydrogen

• Water

• Halogens

How do alkenes react with hydrogen?

Alkene + H₂ → Alkane

They have to be reacted in the presence of a catalyst and moderately high temperature.

They react to form alkanes

How do alkenes react with water?

They can react with steam to form alcohol

This requires a catalyst and high temperature

Alkene + H₂O → Alcohol

(As alcohol’s functional group is OH)

How do alkenes react with halogens?

They can react with halogens to form a dihaloalkane (two alkane atoms, two carbon atoms and four hydrogen atoms).

This doesn’t require high temperature or a catalyst.

Eg. bromine water (orange to colourless when reacted with an alkene)

Draw fully displayed structural formulae of propene (alkene) and the products of its addition reaction with hydrogen

Draw fully displayed structural formulae of ethene (alkene) and the products of its addition reaction with water

Draw fully displayed structural formulae of ethene (alkene) and the products of its addition reaction with a halogen

What is the functional group for alcohols?

OH

What are the first four members of the homogolous series of alcohols?

Methanol, ethanol, propanol, butanol

Draw ethanol

Describe what happens when an alcohol reacts with sodium (with an example)

alcohol + sodium → alkoxide + hydrogen

eg. ethanol + sodium → sodium ethoxide + hydrogen

As hydrogen is produced bubbles of the gas are given off

The alkoxide remaining is a colourless solution.

Describe what happens when an alcohol is burned in air

When an alcohol is burned in air, this is a complete combustion reaction (as it has enough oxygen from the air).

alcohol + oxygen → carbon dioxide + water

Does alcohol react with water? What happens

Alcohols do not react with water and instead dissolve in water to create a colourless, neutral solution (pH of 7)

What’s an oxidising agent?

In terms of oxygen: provides oxygen to a substance in a chemical reaction

In terms of electrons: causes a substance to lose electrons by gaining the electrons that the substances loses

Describe what happens when an alcohol reacts with an oxidising agent (with an example)

Alcohols are oxidised to produce carboxylic acids and water

alcohol + oxygen → carboxylic acid + water

Give the main uses of the first four alcohols

Methanol:

• solvent, fuel, chemical feedstock

Ethanol:

• solvent, fuel, alcoholic drinks

Propanol:

• solvent, antiseptic in hand sanitiser

Butanol:

• Solvent, fuel, chemical feedstock

How are aqueous solutions of alcohol produced? give the formula

When sugar solutions are fermented using yeast

sugar → ethanol + carbon dioxide

Described the conditions required for the fermentation of sugar (using yeast) to produce ethanol

• Anaerobic conditions (no oxygen)

• Temperature between 25 and 40 degrees (as not to denature enzymes

• Must have a sugar source (sugars dissolved in water and mixed with the yeast)

• Time (the reaction is very slow)

What is the functional group for carboxylic acids?

COOH

What are the first four members of the homogolous series of carboxylic acids?

Methanoic acid, ethanoic acid, propanoic acid, butanoic acid

Give the formula for ethanoic acid

CH₃COOH

What happens when carboxylic acids react with carbonates?

carboxylic acid + carbonate → salt + carbon dioxide + water

ethanoic acid + sodium carbonate → sodium ethanoate + carbon dioxide + water

Fizzing and bubbling as carbon dioxide is released

What happens when carboxylic acids dissolve in water?

Carboxylic acids are partially ionised in water (as they are weak acids) forming weakly acidic solutions.

Are carboxylic acids strong or weak acids?

Weak

What happens when carboxylic acids react with alcohols?

Esterification

carboxylic acid + alcohol → ester + water

ethanoic acid + ethanol → ethyl ethanoate + water

They need an acid catalyst to react

What are esters?

Compounds formed from when carboxylic acids react with alcohols; they have fruity smells and are used in perfumes and flavourings.

What are carboxylic acids?

They are weak organic acid compounds that contain the COOH functional group

Give the name of an ester

Ethyl ethanoate

Define polymerisation and what are the two types?

Polymerisation is a process where small simple molecules (monomers) join together repeatedly to form long chain molecules (polymers)

• addition polymers

• condensation polymers

What type of polymerisation do alkanes and alkenes undergo?

Addition polymerisation

Describe addition polymerisation

A reaction where many small unsaturated molecules (molecules that have at least one double covalent bond) (monomers) join together to form very large molecules (polymers)

The molecules are all of the same type

Must have a carbon-carbon double covalent bond in the monomer

No other molecules are produced

In addition polymers the repeating unit has the same atoms as the monomer because no other molecule is formed in the reaction

How to draw the displayed formula of a monomer vs polymer

Monomer: draw it, put brackets around it and an n in front of it

Polymer: draw it, put bracktes around it, have bonds coming outside of the brackets, have an n behind it

Describe condensation polymerisation

A reaction where monomers with two functional groups react together to repeatedly join and form long chain polymers and a small molecule (usually water) is released.

For every new bond between molecules, a small molecule is lost

What do amino acids react to produce?

A polypeptide

What is DNA and what does it do?

Deoxyribonucleic acid is a large molecule (polymer) that encodes genetic instructions for the development and functioning of living organisms and viruses

Describe the structure of DNA

DNA molecules are made up of two polymer chains made from four different monomers called nucleotides, in the form of a double helix.

Name naturally occuring polymers important for life

• DNA (nucleotides)

• proteins (amino acids)

• starch (sugars)

• cellulose (sugars)