topic 6c: alkenes

Question 1

general formula alkene

Answer 1

cnh2n

Question 2

alkene description

Answer 2

unsaturated hydrocarbon

Question 3

c=c bond consists of (interms of bonding)

Answer 3

one sigma
one pi bond

Question 4

how is a sigma bond formed

Answer 4

1 sp2 orbital from each carbon overlaps to form a single c-c sigma

Question 5

how is a pi bond formed

Answer 5

sideways overlap of 2 p orbitals on each C. pi bond formed above and below the plane of the molecule
RESTRICTED ROTATION

Question 6

is pi or sigma stronger

Answer 6

SIGMA

Question 7

PI BOND ELECTRON DENSITY

Answer 7

• high ed
• above and below the line between the 2 nuclei

Question 8

ELECTROPHILE

Answer 8

electron pair acceptor
- pi bonds are vulnerable to attack by them because theyre exposed w high electron density

Question 9

alkene + hydrogen

Answer 9

• addition
• nickel catalyst
  -forms alkane

Question 10

alkene + halogen

Answer 10

• halogen reagent
• room temp
• forms dihalogenoalkane

Question 11

alkene + hydrogen halide

Answer 11

• hydrogen halide reagent
• room temp
  forms alogenoalkane

Question 12

alkene + potassium manganate (VII)

Answer 12

• KMnO4 reagent in an acidified solution
• room temp
• OXIDATION
• forms a diol
  PURPLE MnO4- COLOUR GONE

Question 13

bromine water + alkene

Answer 13

reagent: bromine dissolved in water
- addition
- bromine water decolourises from orange to colourless

Question 14

alkene + steam

Answer 14

• acid catalyst - CONCENTRATED H3PO4
• High temp 300-600
• high pressure 70 atm
• hydration
• alcohol

Question 15

what does heterolytic bond fission form

Answer 15

ions

Question 16

addition polymers are formed from …

Answer 16

alkenes

Question 17

why are polyalkenes unreactive

Answer 17

strong c-c c-h bonds

Question 18

recycling of polymers

Answer 18

• saves raw materials
• polymers need sorting/collecting
• careful separation needs to be done. can only be recycled into the same type

Question 19

incineration of waste polymers

Answer 19

• burnt and energy produced genrates electricity
• releases toxins, greenhouse gases
• reduces volume of rubbish

Question 20

waste polymers as feedstock for cracking

Answer 20

• polymers cracked into small molecules used to make other things
• saves raw materials

Question 21

2 ways chemists limit the problems caused by polymer disposal

Answer 21

1. developing biodegradable polymers
2. removing toxic waste gases caused by incineration of plastics

Question 22

biodegradable polymers

Answer 22

• can biodegrade
• made from maize + starch

Question 23

how do chemists remove the toxic waste gases caused by the incineration

Answer 23

waste cases reacted with a base/carbonate. neutralises it

Question 24

why is the empirical formula of the polymer the same as that of the repeating unit

Answer 24

• addition polymerisation
• no small molecules formed

Question 25

atom economy of addition polymerisation

Answer 25

100%
- addition polymerisation
- no small molecules formed (no co products)