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Question 1

Alkanes

Answer 1

The simplest type of hydrocarbons are called alkanes. Alkanes are a homologous series of compounds made up of chains of carbon atoms surrounded by hydrogen atoms.
In alkanes, carbon atoms form four bonds and hydrogen atoms only form one bond. There are no carbon-carbon double bonds so all the atoms have formed bonds with as many other atoms as they can saturated. - this means they’re
Different alkanes have chains of different lengths. The first four alkanes are methane, ethane, propane and butane. Methane has just one carbon atom and four hydrogen atoms, so its chemical formula is CH4. The green lines in this structure represent covalent bonds.
Ethane (C₂H6) has a chain of two carbon atoms, propane (C3H8) has three carbon atoms and butane (C₄H10) has four carbon atoms.

Question 2

General formula of alkanes

Answer 2

Alkanes all have the general formula CnH2n+2. In this formula, n is the number of carbon atoms. So if an alkane has n carbon atoms, it will always have 2n + 2 hydrogen atoms.

Question 3

Alkenes

Answer 3

Alkenes are a homologous series of hydrocarbons. They’re more reactive than alkanes. All alkenes contain the functional group C=C, a double covalent bond between two of the carbon atoms in their chain
Alkenes are known as unsaturated because they contain a C=C double bond. This can open up to become a single bond, allowing the two carbon atoms to bond with other atoms.
The first three alkenes are ethene (with two carbon atoms), propene (three carbon atoms) and butene (four carbon atoms)

Question 4

General formula of alkenes

Answer 4

All alkenes have the general formula C₂H₂n - they have twice as many hydrogens as carbons. You can use this general formula to recognise alkenes.
If a molecule only has hydrogen and carbon atoms in it, and there are twice as many hydrogens as carbons, then it must be an alkene. You can also recognise alkenes from a displayed formula by looking out for the carbon-carbon double bond.

Question 5

The addition of bromine

Answer 5

All alkenes can react with bromine in addition reactions. The double bond will open up, leaving a single bond, and each of the carbon atoms involved in the double bond will form a single bond with a bromine atom.

Question 6

Test for alkenes

Answer 6

The addition of bromine to alkenes can be used to distinguish alkenes from alkanes. When orange bromine water is added to alkanes and they are shaken together, no reaction will happen and it’ll stay bright orange. If it’s added to alkenes and shaken, the addition reaction above occurs and the bromine water is decolourised bromine is added across the double bond.

Question 7

Complete combustion of hydrocarbons

Answer 7

If you burn hydrocarbons, the carbon and hydrogen react with oxygen from the air to form carbon dioxide and water. The carbon and hydrogen are said to be oxidised. Energy is also released.
When there’s plenty of oxygen, all the carbon atoms are completely oxidised this is called complete combustion. This is the equation for the complete combustion of a hydrocarbon:
hydrocarbon + oxygen -> carbon dioxide + water

Question 8

What are Polymers?

Answer 8

Polymers are substances with high relative molecular mass made by joining up lots of small repeating units called monomers.

Question 9

How to make polymers using alkenes

Answer 9

Alkenes can form polymers by addition polymerisation. This is when lots of small alkene molecules open up their double bonds and join together to form long-chain molecules. The alkene molecules are the monomers and the long-chain molecule is the polymer.

Question 10

Naming polymer

Answer 10

The name of the polymer comes from the type of monomer it’s made from you just stick the word ‘poly’ in front of it and put the monomer name in brackets. So propene becomes poly(propene).
To get the formula of the polymer, you just put the formula of the monomer in brackets and put a little ‘n’ after it. So C3H6 becomes (C3H6n)

Question 11

Properties of polymers

Answer 11

• Poly(tetrafluoroethene) (PTFE)
• poly(chloroethene) (PVC)
• poly(ethene)
• poly(propene)
• are addition polymers. Each polymer has its own set of properties.

Question 12

Poly(ethene)

Answer 12

• Properties -flexible, electrical insulator, cheap
• Uses - plastic bags, bottles, wire insulation

Question 13

Poly(propene)

Answer 13

• Properties -flexible, strong, tough, mouldable
• Uses - crates, furniture, ropes

Question 14

Poly(chloroethene) (PVC)

Answer 14

• Properties -tough, cheap
• Uses - window frames, water pipes

Question 15

Poly(tetrafluoroethene) (PTFE)

Answer 15

• Properties -unreactive, tough, non-stick
• Uses - non-stick pans, waterproof clothing

Question 16

Making condensation polymers

Answer 16

Condensation polymerisation involves monomers which contain two functional groups. A functional group is a group of atoms that are responsible for the chemical properties of a compound. When the monomers react together, bonds form between them, making polymer chains. For each new bond that forms, a small molecule (for example, water) is lost. This is why the process is known as condensation polymerisation.

The simplest types of condensation polymers contain two different monomers, each with two of the same functional group.

Question 17

Polyesters

Answer 17

Dicarboxylic acid monomers can react with diol monomers to form ester links this is a condensation reaction. The dicarboxylic acid monomers contain two carboxylic acid groups (-COOH) and the diol monomers contain two alcohol groups (-OH).

The molecule with the ester link has a functional group at each end. These can then react in condensation reactions, making the chain longer. The series of reactions together is known as condensation polymerisation and the resultant polymer is called a polyester.

Question 18

Naturally Occurring Polymers - DNA

Answer 18

DNA (deoxyribonucleic acid) is found in every living thing and many viruses. It contains genetic instructions that allow the organism to develop and operate. It’s a large molecule that takes a double helix structure.

DNA is made of two polymer chains of four different types of monomers called ‘nucleotides’. The order of the nucleotides acts as a code for the organism’s genetic information.

Question 19

Naturally Occurring Polymers - Amino acids and proteins

Answer 19

An amino acid contains two different functional groups a basic amino group (NH₂) and a carboxylic acid group (COOH).

Amino acids can form polymers known as proteins by polymerisation. The amino group of an amino acid can react with the acid group of another, and so on, to form a polymer chain. For every new bond that is formed a molecule of water is lost, so it’s condensation polymerisation

Question 20

Naturally Occurring Polymers - Carbohydrates and starch

Answer 20

Carbohydrates are molecules containing carbon, oxygen and hydrogen, used by living things to produce energy.

A complex carbohydrate, starch, is a polymer made up of many smaller units of carbohydrates, known as sugars, joined together in a long chain.

Question 21

The raw materials of polymers

Answer 21

Plastics are made from crude oil. Crude oil is a finite resource, eventually it will all get used up and run out. The more we use up our crude oil resources, the more expensive crude oil will become. This will then increase the price of crude oil products.

Crude oil isn’t just used to make plastics, we need it for lots of different things, such as petrol for cars and heating our homes. As resources dry up, we will face the dilemma of how to use the remaining oil. One way we can help delay this problem is by recycling our polymers.

Question 22

Disposing of polymers in landfill sites

Answer 22

A lot of plastics get dumped in landfill sites. This is usually when different polymers are too difficult or expensive to separate and recycle. There are some problems with disposing of polymers in this way:
* Lots of valuable land is quickly getting used up for use as landfill sites.
* Most polymers are non-biodegradable - they’re not broken down by microorganisms. This means that they will sit in landfill for years and years and years and years…

Question 23

Disposing of polymers by combustion

Answer 23

Burning plastics releases a lot of energy and this can be used to generate electricity or heat local homes. However, if not carefully controlled, toxic gases can be released from the combustion of plastics.

Example - When polymers that contain chlorine (such as PVC) are burned, they produce HCI - this has to be removed. Carbon dioxide is also produced and this contributes to global warming.

Question 24

Recycling Polymers - pros

Answer 24

It reduces the amount of non-biodegradable waste filling up landfill sites

It reduces emissions of greenhouse and toxic gases which can be released from burning polymers.

Recycling generally uses up less water and energy resources than making new plastics does.

It reduces the amount of crude oil needed to produce more plastics.

Recycling generally saves money and creates jobs.

Question 25

Recycling Polymers - cons

Answer 25

Polymers must be separated by type before they can be melted and reformed into a new product - this can be difficult and expensive.

It can be more expensive than producing new products from raw materials.

If polymers are mixed together, the quality of the final recycled polymer product could be reduced.

Polymers can only be recycled a finite number of times. Over time, the strength of the polymer can decrease.

Melting down polymers can release dangerous gases into the atmosphere. These are harmful to plants and animals.