alkene 14

Question 1

alkene

Answer 1

unsaturated hydrocarbon
made of carbon and hydrogen only
more reactive than alkane = high concentration of electrons
(Bonding in alkenes involves a double covalent bond, a centre of high electron density)

Question 2

structure

Answer 2

planar molecule
angle 120 degrees
no rotation around the double bond

Question 3

double bond can’t rotate

Answer 3

two orbitals overlap to form an orbital with a cloud of electron density above and below the single bond

Question 4

tips on naming

Answer 4

groups are listed alphabetically

Question 5

physical properties

Answer 5

van der waals forces are only intermolecular forces
melting and boiling point increase with the number of carbons
not soluble in water

Question 6

electrophile

Answer 6

electron pair acceptor

Question 7

react

Answer 7

alkenes more reactive than alkane

Question 8

electrophilic addition

HBr, H2SO4 and Br2

Answer 8

1 electrophile is attracted to the double bond
2 electrophiles are positively charged and accept a pair of electrons from the double bond.
3 a positive ion is formed (carbocation)
4 negatively charged ion forms a bond with the carbocation

Question 9

most stable carbocation

Answer 9

tertiary
secondary
primary

Question 10

test for a double bond

Answer 10

bromine solution (reddish-brown) goes colourless

Question 11

additional polymers

Answer 11

made of monomers

eg poly(ethene)

Question 12

use of poly(ethene)

Answer 12

carrier bags

washing up bowls

Question 13

use of poly(propene)

Answer 13

yoghurt containers

car bumpers

Question 14

use of poly(chloroethene)

PVC

Answer 14

aprons
vinyl records
drainpipes

Question 15

use of poly(propenenitrile)

Answer 15

clothing fabrics

Question 16

use of poly(phenylethene)

Answer 16

packing materials
electrical insulation
(Making poly(phenylethene) from phenylethene.)

Question 17

modifying plastics

Answer 17

properties can be modified by using additives such as a plasticisers, forcing the chains apart and allowing them to slide over each other

Question 18

biodegradability

Answer 18

unreactive so are not attacked by biological agents so they are not biodegradable

Question 19

Low-density polyethene

Answer 19

high pressure and high temperature via free-radical mechanism
the branched chains do not pack together well so its flexible, stretches well and low density

Question 20

High-density polyethene

Answer 20

temperature and presses little greater than room conditions
Ziegler-Natta catalyst
less chain branching
the chains pack together well

Question 21

mechanical recycling

Answer 21

separate different types of plastics
plastics are then washed and sorted
make into small pellets
melted and reused

Question 22

feedstock recycling

Answer 22

heated to a temperature where the bonds will break and used as a new plastics
some materials can be heated a limited number of times because some of the chains break degrading the plastics properties

Question 23

alkene and oxygen

Answer 23

combustion

would make carbon dioxide and water

Question 24

alkene and water

Answer 24

hydrolysis 
CH2=CH2(g) + H2O (g) ---- CH3CH2OH (g)
stream
pressure
acid catalyst
suitable temperature

Question 25

alkene and hydrogen halides

Answer 25

electroplic addition

CH2=CH2 + HCl ——- CH3CH2Cl

Question 26

alkene and halogens

Answer 26

electrophilic addition
CH2=CH2 + Br2 —- CH2BrCH2Br
dipole caused by getting close to the double bond

Question 27

Alkenes and concentrated sulphuric acid

Answer 27

electrophilic addition

CH2=CH2 + H2SO4 —— CH3CH2OH + H2SO4

Question 28

formation of major and minor products

Answer 28

The formation of major and minor products in addition reactions of unsymmetrical alkenes

Question 29

formations of addition polymers

Answer 29

Addition polymers are formed from alkenes and substituted alkenes.

Question 30

properties of addition polymers

Answer 30

unreactive