Alkenes (Chapter 14)

Question 1

What are alkenes?

Answer 1

Unsaturated hydrocarbons (double bond)

Question 2

Describe the bonding in alkenes

Answer 2

Involves a double covalent bond (centre of high electron density)

Question 3

What is used to test if a hydrocarbon is saturated?

Answer 3

Bromine water which turns colourless (as double bond is broken and bromine substituted onto alkene.)

Question 4

What is the formula for alkenes?

Answer 4

CnH2n

Question 5

Why do alkenes have stereoisomers?

Answer 5

The overlapping pi bond restricts rotation around the double bond.

Question 6

Define electrophile

Answer 6

An electron pair acceptor.

Has partial or full charge so is electron deficient

Question 7

Compare the properties of E vs Z isomers

Answer 7

E isomers can pack together more easily, so have stronger intermolecular forces and therefore tend to have higher melting points.

Question 8

What reaction forms haloalkenes?

Answer 8

Electrophilic addition reactions

Question 9

What is a primary carbon cation?

Answer 9

Positively charged carbon on the end of a hydrocarbon

Question 10

What is a secondary carbon cation?

Answer 10

Positive charge carbon within hydrocarbon chain (bonded to two other carbons).

Question 11

What is a tertiary carbon cation?

Answer 11

Positively charged carbon in a carbon chain with alkyl group (bonded to 3 other carbons).

Question 12

Order the carbon cations from least to most stable

Answer 12

Primary - least
Secondary
Tertiary - most

Question 13

How are priority groups assigned?

Answer 13

By their atomic number

Question 14

What forces are between alkenes?

Answer 14

Weak Van-der-Waals forces

Question 15

What is the pattern for boiling points in alkenes?

Answer 15

The more carbons then the higher the boiling point.

Question 16

Describe the stages in an an electrophilic addition reaction

Answer 16

1) The electrophile is attracted to the double bond.
2) Electrophiles are positively charged and accept a pair of electrons from the double bond. (May be a positive ion or have a positively charged area)
3) A positively charged carbon (cation) is formed.
4) A negatively charged ion forms with the carbocation.

Question 17

What is meant by heterolytic bond breaking?

Answer 17

When a covalent bond breaks and both electrons go to one of the atoms involved and none to the other. This results in a positive and negative ions being formed.

Question 18

What is a positive inductive effect?

Answer 18

The idea that alkyl groups have a tendency to release electrons.

Question 19

What is produced when water is reacted with an alkene?

Answer 19

Alcohol

Question 20

How is a polymer drawn?

Answer 20

Square brackets around the monomer with broken double bond and n next to brackets or number of repeating units.

Question 21

What are plasticisers?

Answer 21

Small molecules that get between the polymer chains forcing them apart and allowing them to slide across each each other.

Question 22

How is low density (poly)ethene made?

Answer 22

Polymerising ethene at high pressure and high temperature via free radical mechanism.

Question 23

Describe the properties of low density poly(ethene)

Answer 23

Do not pack together and are quite flexible and stretch easily.

Question 24

What are some uses for low density poly(ethene)?

Answer 24

Packaging (e.g. plastic bags), sheeting and electrical cables.

Question 25

How is high density (poly)ethene made?

Answer 25

Slightly higher temperature and pressure and than room temperature and use a Ziegler-Natta catalyst.

Question 26

Describe the properties for high density

Answer 26

Few branches (about 1/200 carbons). Can pack together well so the density of plastic greater and its melting point is higher.

Question 27

What are some uses for high density poly(ethene)?

Answer 27

Milk crates and bottles

Question 28

What is mechanical recycling?

Answer 28

Melting and remoulding poly(ethene)

Question 29

What is feedstock recycling?

Answer 29

Heating poly(ethene) to a temperature that breaks the bonds and making new plastics.

Question 30

Describe the steps of mechanical recycling

Answer 30

1) Different plastics are separated 2) Plastics washed and ground into pellets. 3) Melted and remoulded e. g. drinks bottles made into fleece clothing

Question 31

What is a problem with feedstock recycling?

Answer 31

It can only be carried out a limited number of times because at each heating some of the chains break and become shorter therefore degrading the plastic's properties.

Question 32

What is a stereoisomer?

Answer 32

Compounds/molecules with the same structural formula but with atoms/bonds/groups arranged differently in space

Question 33

What is an addition reaction?

Answer 33

Reaction which increases number of substituents or converts a double bond to single bond.

Question 34

What is poly(chloroethene) used for?

Answer 34

Rigid plastic as strong intermolecular bonding but its plasticiser is can be used as PVC as intermolecular bonds are broken.

Question 35

What are the properties of poly(chloroethene)?

Answer 35

Waterproof, electrical insulator and doesn't react with acid.