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Chemistry A-Level OCR > 4.1.3 alkenes > Flashcards

4.1.3 alkenes Flashcards

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1
Q

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

A

hydrogen

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2
Q

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

A

nickel

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3
Q

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

A

alkane

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4
Q

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

A

halogen

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5
Q

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

A

dihaloalkane

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6
Q

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

A

reaction with bromine water where alkenes decolourise bromine water

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7
Q

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

A

hydrogen halide

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8
Q

what is hydration

A

addition of water to a molecule

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9
Q

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

A
  • H3PO4 catalyst
  • 300°C
  • 60atm
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10
Q

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

A

steam

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11
Q

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

A

reversible

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12
Q

give the product of a reaction between an alkene and steam

A

alcohol

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13
Q

define alkene

A

unsaturated hydrocarbons contain at least one carbon to carbon double bond

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14
Q

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

A

trigonal planar 120°

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15
Q

what two bonds are c=c bonds made up of

A

sigma and pi bonds

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16
Q

why are pi bonds vulnerable to attack from electrophiles

A

they are exposed and have high electron density

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17
Q

how is the pi bond formed

A

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

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18
Q

which bond is weaker sigma or pi

A

pi

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19
Q

alkenes induce strong dipoles on which molecules

A

halogens

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20
Q

what is stereoisomerism

A

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

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21
Q

what kind of isomerism do alkenes exhibit

A

e-z

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22
Q

why do stereoisomers arise

A
  • 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

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23
Q

give the steps of the cahn-ingold prelog rules

A

1) split in the middle

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

24
Q

why do cis-trans isomers arise

A
  • 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
25
Q

define electrophile

A

electron pair acceptor

26
Q

what is an addition reaction

A

where two molecules react to make one molecule

27
Q

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

A

it becomes polar and electrophilic

28
Q

what does an intermediate molecule have within it

A

a positively charged carbon atom called a carbocation

29
Q

what type of fission do addition reactions of alkenes include

A

heterolytic

30
Q

what are the mechanisms in the addition reactions of alkenes called

A

electrophilic addition mechanism

31
Q

define addition

A

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

32
Q

describe the steps of the electrophilic addition mechanism

A
  • 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
33
Q

what is the order of stability for carbocations

A 
most stable 
                    tertiary 
                    secondary 
                    primary 
least stable
34
Q

why is the carbocation intermediate more stable

A

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

35
Q

explain why a particular major product is formed

A

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

36
Q

what is hydration

A

addition of water to a molecule

37
Q

hydration is what type of reaction

A

reversible

38
Q

why is hydration of alkenes done industrially

A

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

39
Q

give the basic template of addition polymers

A 
|    |
n c=c  ——>
   |    |
                |   |
bracket -c-c- bracket n 
                |   |
40
Q

why are polyalkenes unreactive

A

they have strong c-c and c-h bonds

41
Q

how is margarine formed

A

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

42
Q

what are the benefits or crude oil derived plastics

A

cheap -less energy needed

purer -less separation

43
Q

what are drawbacks if crude oil derived plastics

A

non-biodegradable -landfill

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

44
Q

how does recycling work

A

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

45
Q

how can waste polymers be used in cracking

A

as feedstock which allows for production of plastics and other chemicals

46
Q

how can waste polymers be used for energy production

A

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

47
Q

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

A

toxic, acidic waste products

can remove the fumes formed by reacting with an alkaki eg CaO

48
Q

give the names of four other types of polymer

A

biodegradable
compostable
soluble
photodegradable

49
Q

what are the benefits of using renewable resources

A

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

50
Q

what are the drawbacks of biodegradable polymers

A

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

51
Q

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

A

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

52
Q

why are alkenes highly reactive

A
  • 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
53
Q

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

A

electrophilic addition

54
Q

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

A

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

55
Q

give 2 uses of alkenes

A
  • making margarine

- forming polymers

Chemistry A-Level OCR (28 decks)

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