Alkenes

Question 1

What is the general formula for alkenes?

Answer 1

CnH2n

Question 2

What are alkenes?

Answer 2

Unsaturated hydrocarbons

Question 3

What alkenes contain?

Answer 3

They are hydrocarbons so the ONLY contain hydrogens and carbons.

Question 4

Why are alkenes unsaturated?

Answer 4

There is at least 1 double covalent bond.

Question 5

What reactions do alkenes undergo?

Answer 5

Addition reaction

Question 6

How do we test for alkenes?

Answer 6

Adding bromine water to an alkene causes a colour change from brown-orange to colourless.

Question 7

What happens when alkenes reacting with COLD and CONCENTRATED sulfuric acid?

Answer 7

Alkyl hydrogen sulfates - H2SO4 acts as a catalyst to make an alcohol from an alkene.

Question 8

Alkenes are ________ which join to form ________.

Answer 8

1. monomers
2. polymers

Question 9

Polymers can either be…

Answer 9

Natural or synthetic

Question 10

What are natural polymers made of?

Answer 10

Proteins and natural rubber

Question 11

What are synethtic polymers made of?

Answer 11

Poly(ethene) and poly(propene)

Question 12

Name 5 properties of polyalkenes

Answer 12

1. Most polyalkene chains are non-polar so they only have van der waals’ between the chains
2. The longer the chain and the closer they are the eachother the more van der waals’ forces there are
3. Polymer chains which are shorter and have a lot of branching tend to be more flexible and weaker.
4. Polymers with no or very little branching and long tend to be more rigid and stronger.
5. Some polyalkenes have halogens so they can form stronger permanent dipole-dipole forces and so will have different strength to other, non-polar polyalkenes.

Question 13

How can plasticisers change the properties of polyalkenes?

Answer 13

They slide between the polymer chains by pushing them apart, which makes the polymer more flexible. They weaken the intermolecular forces in between them so they chains can easily slide over eachother which makes the polymer easier to bend.

Question 14

Give one example of a polyalkene in which plasticisers are used.

Answer 14

PVC - poly(chloroethene)
It is made from long, closely packed polymer chains that are hard but brittle and are used in drain pipes. PVC has a plasticiser that makes it more flexible and so it can be used for electrical cable insulation and clothing.