organic chemistry

What is a hydrocarbon?

- A compound which contains hydrogen and carbon atoms ONLY

What does the molecular formula show?

- Exact number of atoms of each element present in a compound

What does the empirical formula show?

- Simplest ratio of atoms of each element present in a compound

What does the general formula show?

- Relationship between the number of atoms of each element within a molecule

What does the structural formula show?

- How the atoms in a compound are joined together

What does the displayed formula show?

- A drawing of the bonds within a compound

What is a functional group?

- An atom or group of atoms which determine the chemical properties of a compound

What is a homologous series?

- Group of compounds with same chemical properties because they have same functional group

- e.g. alcohols (-OH), alkenes (C=C)

What do members of the same homologous series have in common?

- Same chemical properties

- Trend in physical properties

- Same functional group

- Same general formula

What does isomerism mean?

- Compounds with same molecular formula but different displayed/structural formula

What is crude oil made up of?

- Mixture of hydrocarbons

What is a fraction?

- Group of substances with similar boiling points

How is crude oil separated into its various fractions?

- Fractional distillation

- Crude oil is heated

- Crude oil boils and vaporises

- Vapour passed into bottom of fractionating column

- Column hottest at the bottom - longest chain fractions condense here e.g. bitumen

- Column coolest at the top - shortest chain fractions condense here e.g. refinery gases

What are the main uses of the following fractions:

- Refinery gases (mixture of methane ethane, propane) - bottled gas

- Gasoline - fuel for cars

- Kerosene - fuel for planes

- Diesel - fuel for buses, lorries

- Fuel oil - fuel for ships

- Bitumen - road surfacing

What does viscosity mean?

- How readily a liquid flows

- e.g. honey - very viscous

- e.g. water - not very viscous

What does volatile mean?

- Evaporates readily

Compare the colour of bitumen and refinery gases

Bitumen = Dark

Refinery = Light

Compare the viscosity of bitumen and refinery gases

Bitumen = Very viscous

Refinery = Not viscous

Compare the boiling point of bitumen and refinery gases

Bitumen = High

Refinery gases = Low

What is a fuel?

- Substance which releases energy when burnt

What is complete combustion?

- Burning in plentiful oxygen

- Produces carbon dioxide and water

What is incomplete combustion?

- Burning in insufficient oxygen

- Produces carbon monoxide and water

- e.g. ethane + oxygen → carbon monoxide + carbon + water

Why is incomplete combustion a problem?

- Carbon monoxide is made - poisonous gas

- Combines irreversibly with haemoglobin

- Less oxygen transported in blood

How are oxides of nitrogen formed?

- High temperatures in car engines

- Cause nitrogen to react with oxygen

- Forms nitrogen oxides

- e.g. nitrogen oxide (NO), nitrogen dioxide (NO2)

Which sulfur oxides are formed by burning sulfur impurities found in crude oil?

- Sulfur dioxide (SO2)

- Sulfur trioxide (SO3)

How is acid rain formed?

- Nitrogen oxides from car engines dissolve in rain water → nitric acid

- Sulfur impurities in crude oil → sulfur dioxide → dissolve in rain water → sulfuric acid

What environmental issues does acid rain (H2SO4) cause?

- Plants die

- Fish die

- Limestone buildings corrode

What is cracking?

- The breaking down of long alkane chains

- Into smaller chain alkanes and alkenes

What reaction conditions are needed for cracking?

- 600-700°C

- Alumina or silica catalyst

Explain why cracking is important

- Produces shorter chain molecules

- Shorter molecules more useful as fuels

- Used to make petrol/diesel for vehicles

- Crude oil richer in long chain molecules

- Alkenes also produced by cracking

- Used to make alcohols / polymers / plastics

What is the general formulae of an alkane?

- CnH2n+2

Why are alkanes classified as ‘saturated’ hydrocarbons?

- All carbons form 4 single bonds

- No C=C double bonds

Describe the reaction of alkanes with halogens

- Substitution reaction

- UV radiation required

Give the equation for the reaction of methane with bromine

- Methane + bromine → bromomethane + hydrogen bromide

- CH4 + Br2 → CH3Br + HBr

What is the functional group of the alkenes?

C=C

What is the general formulae of an alkene?

- CnH2n

What does the ‘1’ in but-1-ene mean?

- Double bond attached to the first carbon in the chain

Why are alkenes classified as ‘unsaturated’ hydrocarbons?

- Contain C=C double bonds

What is the test for an unsaturated compound (an alkene)?

- Add compound to bromine water

- Orange colour turns colourless

- This is an addition reaction

- Dibromoalkane formed as product

Give the equation for the reaction of ethene with bromine water

- Ethene + bromine → dibromoethane

- C2H4 + Br2 → C2H4Br2

Describe how to use bromine water to distinguish between an alkane and an alkene

- Add bromine water to each compound

- If bromine water turns colourless → compound is an alkene

Why don’t alkanes turn bromine water colourless?

- Alkanes have no double bond (they’re saturated)

Define monomer

A small molecule that joins together to form a polymer

Define polymer

A long chain formed from many small molecules joined together

What is an addition polymer?

- A polymer made from the joining up of many monomers

How are addition polymers formed?

- One bond in the double bond break

- Monomers join together

- Form a long chain containing only single bonds

Give a use for common addition polymers

- Poly(ethene) - plastic bags

- Poly(propene) - plastic water pipes

- Poly(chloroethene) - window frames (PVC)

- Poly(tetrafluorine) - non-stick pan coating

What does biodegradable mean?

Can be broken down using microorganisms

What are the difficulties with the disposal of addition polymers?

- Inert (unreactive)

- Means they do not-biodegrade

- When burned give off toxic gases