alkenes

Question 1

what are alkenes

Answer 1

unsaturated hydrocarbons with the general formula of CnH2n

Question 2

what makes alkenes reactive

Answer 2

double bonds have a high electron density

Question 3

why are alkenes attacked by electrophiles

Answer 3

their double bond and the electrophile adds to the molecule

Question 4

what are electrophiles

Answer 4

an electron pair acceptor
they are deficient in electrons and are attracted to the double bond

Question 5

examples of electrophiles

Answer 5

positive charge ions, polar molecules

Question 6

what is the test for alkenes

Answer 6

addition of bromine- decolorisation of bromine water
bromine is the electrophile and adds to the alkene forming a dibromoalkane
Br is polarised as when come into contact double bond (area with lots of electrons) repels to become polar
electron pair in the double bond attracted to positive bromine and forms bond breaking Br-Br bond
a carbocation intermediate is formed and Br- attracted to positive C
forms colourless 1 2 dibromoethane

Question 7

alkenes react with hydrogen halides to form …

Answer 7

halogenoalkanes

Question 8

reactions with .. alkenes produces 2 different products

Answer 8

unsymmetrical

Question 9

the amount of the 2 products is determined by the … of the … intermediate

Answer 9

stability
carbocation

Question 10

the more … groups bonded to the carbocation the more stable the intermediate is

Answer 10

alkyl

Question 11

why do alkyl groups make it more stable

Answer 11

because alkyl groups push electrons towards the positive carbocation stabilising it. the more stable the carbocation the more likely it will form

Question 12

what is a tertiary carbocation

Answer 12

three alkyl groups pushing electrons towards the carbocation

Question 13

alkenes react with … sulfuric acid to form…

Answer 13

cold concentrated
alkyl hydrogen sulfates

Question 14

H2SO4 is used as a … in making an alcohol from an alkene

Answer 14

catalyst

Question 15

making alcohol from alkyl hydrogen sulfates

Answer 15

adding cold water to warm ethyl hydrogen sulphate will form ethanol- hydrolysis
ethyl hydrogen sulfate => ethanol and sulfuric acid reformed

Question 16

polymers can be … or …

Answer 16

natural- proteins and natural rubber
synthetic- polyethane and polypropene

Question 17

what did Charles Goodyear do

Answer 17

discovered vulcanized rubber by adding chemicals to natural rubber to make stronger rubber for tyres

Question 18

how have polymers been developed for use

Answer 18

polyethane
nylon
teflon
still being made for new tech

Question 19

how to make polypropene

Answer 19

the monomer propene
the double bond opens up to form polymer

Question 20

polyalkenes properties

Answer 20

saturated so normally non polar and hence unreactive
but that means they don’t degrade well in landfill

Question 21

intermolecular forces in polymers

Answer 21

most have only van der waals forces
the longer the chain the more van der waals as they can pack together closer giving higher bpt and are rigid and stronger
shorter more branched chains are more flexible and weaker

Question 22

polyalkenes with halogens intermolecular forces

Answer 22

they can also now form stronger permanent dipole dipole forces eg-PVC

Question 23

what are plasticisers

Answer 23

are added to polymers to change properties making it more flexible

Question 24

how do plasticisers work

Answer 24

they slide between the polymer chains pushing them apart
this weakens the imf and the chains can now slide over each other making it easier to bend