Alkenes

Question 1

describe alkenes homologous series

Answer 1

Homologous series of unsaturated hydrocarbons with general formula CnH2n

Question 2

angles found in alkenes

Answer 2

C=C are planar (120°)

CH3 are tetrahedral (109.5°)

Question 3

reactivity compared to alkanes and reason pls

Answer 3

More reactive than alkanes due to high electron density (two pairs of electrons)

Question 4

unsaturated meaning

Answer 4

contains at least one double bond, a centre of high electron density

Question 5

what type of mechanism for alkenes and why

Answer 5

Electrophilic addition

Occurs due to high electron density so can easily be attacked by electrophiles

Question 6

electrophile

Answer 6

an electron pair acceptor – needs positive charge e.g. protons, acids (H+)

Question 7

addition reaction

Answer 7

reaction where two molecules produce one molecule

Question 8

carbocation

Answer 8

positively charged carbon atom

Question 9

test for unsaturation

Answer 9

use bromine water if alkene it will turn orange -> colourless

Question 10

reagent of reaction from alkene into dibromoalkane

Answer 10

bromine (Br2)

Question 11

conditions for reaction from alkene into dibromoalkane

Answer 11

room temperature, aq

Question 12

what does alkene and bromine make

Answer 12

dibromoalkene

Question 13

stages of reaction from alkene -> alcohol

reagent, conditions

Answer 13

1. reaction with sulphuric acid
   alkene -> alkyl hydrogensulphate
   c. H2SO4
   room temperature, aq
2. reaction with wayer (hydrolysis)
   alkyl hydrogensulphate -> alcohol
   water
   warm

Question 14

what does H2SO4 act as when making an alcohol form alkene

Answer 14

catalyst because it is regenerated at the end

Question 15

reaction from alkene to bromoalkane reagent and conditions

Answer 15

HBr (for chloroalkane HCl)

room temperature, aq

Question 16

Markovnikov’s rule

Answer 16

bromine will be added to the carbon with the fewest hydrogens on it as it is the most stable carbocation intermediate to form major product

Question 17

why could more than one product be produced

Answer 17

Alkene is asymmetrical
Draw out carbocations and identify as primary, secondary and tertiary
State which is the more stable carbocation e.g. secondary more stable than primary
More stable carbocation is stabilized because carbon atoms around carbocation are electron releasing so reduce the charge and stabilises it

Question 18

reaction that converts ethene -> ethane

conditions (3) and use (1)

Answer 18

hydrogenation of ethene

conditions: nickel catalyst, H2 gas, 140°C

used for the hardening of vegetable oil to form fats in the manufacture of margarine

Question 19

monomer

Answer 19

a small molecule that can combine with similar molecules to form a long molecule called a polymer

Question 20

addition polymer

Answer 20

very long molecules made of smaller molecules called monomers are generally unreactive

Question 21

addition polymerisation

Answer 21

the process where monomer join by single bonds to form 1 large polymer molecule

Question 22

types of poly(ethene)

Answer 22

low density poly(ethene)

high density poly(ethene)

Question 23

conditions and structure of low density poly(ethene)

Answer 23

Under high pressures and a trace of oxygen

Polymer chains have random branches so are unable to pack closely together

Question 24

conditions and structure of high density poly(ethene)

Answer 24

Catalyst, 50°C, slightly high pressure

Polymer chains are straighter without branches so are able to pack closely together

Question 25

what are biodegradable polymers

Answer 25

able to be broken down by microorganisms

Question 26

poly(chloroethene) PVC properties and uses

Answer 26

Properties can be modified by a plasticiser
- hard, rigid, tensile strength becomes more flexible and softer

Uses: window frames, pipes