4.1.3 alkenes

Question 1

what is the reagent in a reaction between hydrogen and an alkene ?

Answer 1

hydrogen

Question 2

what catalyst is needed in a reaction between hydrogen and an alkene?

Answer 2

nickel

Question 3

give the basic product of a reaction between hydrogen and an alkene?

Answer 3

alkane

Question 4

what is the reagent in a reaction between a halogen and an alkene?

Answer 4

halogen

Question 5

give the basic product of a reaction between a halogen and an alkene

Answer 5

dihaloalkane

Question 6

what is the test to test for alkenes and what is the outcome

Answer 6

reaction with bromine water where alkenes decolourise bromine water

Question 7

what is the reagent in a reaction between a hydrogen halide and an alkene

Answer 7

hydrogen halide

Question 8

what is hydration

Answer 8

addition of water to a molecule

Question 9

give the three conditions needed for a reaction between an alkene and steam

Answer 9

• H3PO4 catalyst
• 300°C
• 60atm

Question 10

what is the reagent in a reaction between an alkene and steam

Answer 10

steam

Question 11

what type of reaction is the reaction between an alkene and steam

Answer 11

reversible

Question 12

give the product of a reaction between an alkene and steam

Answer 12

alcohol

Question 13

define alkene

Answer 13

unsaturated hydrocarbons contain at least one carbon to carbon double bond

Question 14

give the shape and bond angle of a c=c bond

Answer 14

trigonal planar 120°

Question 15

what two bonds are c=c bonds made up of

Answer 15

sigma and pi bonds

Question 16

why are pi bonds vulnerable to attack from electrophiles

Answer 16

they are exposed and have high electron density

Question 17

how is the pi bond formed

Answer 17

sideways overlap if two p orbitals on each carbon atom forming a pi bond above and below the plane of the molecule

Question 18

which bond is weaker sigma or pi

Answer 18

pi

Question 19

alkenes induce strong dipoles on which molecules

Answer 19

halogens

Question 20

what is stereoisomerism

Answer 20

molecules that have the same structural formula but a different spacial arrangement of atoms

Question 21

what kind of isomerism do alkenes exhibit

Answer 21

e-z

Question 22

why do stereoisomers arise

Answer 22

• there is restricted rotation around the c=c double bond

* there are two different groups/atoms attached to both ends of the restricted double bond

Question 23

give the steps of the cahn-ingold prelog rules

Answer 23

1) split in the middle

2) which atom or group of atoms has higher atomic number

Question 24

why do cis-trans isomers arise

Answer 24

• if the alkene has two groups/atoms that are the same each side of the double bond
• if two groups are in the same plane the molecule is called cis and if not trans

Question 25

define electrophile

Answer 25

electron pair acceptor

Question 26

what is an addition reaction

Answer 26

where two molecules react to make one molecule

Question 27

when the pi bond induces a dipole on a halogen what happens to the halogen

Answer 27

it becomes polar and electrophilic

Question 28

what does an intermediate molecule have within it

Answer 28

a positively charged carbon atom called a carbocation

Question 29

what type of fission do addition reactions of alkenes include

Answer 29

heterolytic

Question 30

what are the mechanisms in the addition reactions of alkenes called

Answer 30

electrophilic addition mechanism

Question 31

define addition

Answer 31

the adding of an atom or group of atoms to a molecule

Question 32

describe the steps of the electrophilic addition mechanism

Answer 32

* c=c double bonds attract electrophiles because of the high electron density * pi bond breaks and a pair of electrons form a bond to the electrophile from one carbon across the double bond * the bond in the electrophile breaks and the electron pair forms a negative ion * ion is attracted to the carbocation intermediate

Question 33

what is the order of stability for carbocations

Answer 33

``` most stable tertiary secondary primary least stable ```

Question 34

why is the carbocation intermediate more stable

Answer 34

the methyl groups in either side of the positive carbon are electron releasing and reduce the charge on the ion that stabilises it

Question 35

explain why a particular major product is formed

Answer 35

the tertiary/secondary carbonium ion intermediate is favoured because it is more stable

Question 36

what is hydration

Answer 36

addition of water to a molecule

Question 37

hydration is what type of reaction

Answer 37

reversible

Question 38

why is hydration of alkenes done industrially

Answer 38

high pressure needed, no waste product- causes high atom economy, separation of products is easier

Question 39

give the basic template of addition polymers

Answer 39

``` | | n c=c ——> | | | | bracket -c-c- bracket n | | ```

Question 40

why are polyalkenes unreactive

Answer 40

they have strong c-c and c-h bonds

Question 41

how is margarine formed

Answer 41

catalytic hydrogenation of unsaturated vegetable oils using hydrogen and a nickel catalyst converts double bonds to single bonds therefore increasing melting point

Question 42

what are the benefits or crude oil derived plastics

Answer 42

cheap -less energy needed | purer -less separation

Question 43

what are drawbacks if crude oil derived plastics

Answer 43

non-biodegradable -landfill | crude oil is non-renewable -being used up hard to replace

Question 44

how does recycling work

Answer 44

polymers are sorted into different types then each type can be recycled by melting and remoulding

Question 45

how can waste polymers be used in cracking

Answer 45

as feedstock which allows for production of plastics and other chemicals

Question 46

how can waste polymers be used for energy production

Answer 46

can be combusted and heat released can be used to generate electricity

Question 47

what forms when waste polymers are combusted and how can this be overcome

Answer 47

toxic, acidic waste products | can remove the fumes formed by reacting with an alkaki eg CaO

Question 48

give the names of four other types of polymer

Answer 48

biodegradable compostable soluble photodegradable

Question 49

what are the benefits of using renewable resources

Answer 49

easily replaced and won’t run out derived from plants -carbon neutral plant based polymers use less energy over their lifetime

Question 50

what are the drawbacks of biodegradable polymers

Answer 50

must be composted in ideal conditions to degrade must be separated from non-biodegradable polymers more expensive

Question 51

draw the mechanism for propene reacting with HBr and state the type of bond fission occurring

Answer 51

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwi2sMTwy4DaAhUEDcAKHfNwCOwQjRx6BAgAEAU&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D-DdAxbfo0uM&psig=AOvVaw15uQEtNm81BsKLTP6SaXD0&ust=1521830749869917

Question 52

why are alkenes highly reactive

Answer 52

- pi bonds are exposed - have high electron density with 2 electron pairs in a double bond with a negative charge that electrophiles are attracted to - can induce a strong dipole on halogen molecules such as bromine

Question 53

what type of mechanism occurs when alkenes react with halides or hydrogen halides

Answer 53

electrophilic addition

Question 54

which product is most likely to form in a reaction between hydrogen halides and alkenes

Answer 54

-the major product is the one where hydrogen adds to the carbon with the most hydrogens

Question 55

give 2 uses of alkenes

Answer 55

- making margarine | - forming polymers