C13 - alkenes

Question 1

formation of a double bond

Answer 1

pi bond forms as p-orbitals overlap (1e- from each carbon)
pi density above & below nuclei of bonding atoms
pi bond locks carbon in place, therefore atoms can’t rotate around a double bond

Question 2

shape around a double bond

Answer 2

trigonal planar
- 3 regions of electron density repel each other
- 120 bond angle
- all atoms in same plane

Question 3

alkene general formula

Answer 3

CnH2n

Question 4

Why does E-Z isomerism exist in double bonds?

Answer 4

due to restriction around double bonds, groups attached to the carbon atoms are FIXED

Question 5

priority rules in E-Z isomerism

Answer 5

priority group attached to C has the highest atomic number

Question 6

unsaturation test

Answer 6

add bromine water (orange/brown) to alkene sample
- double bond decolourises bromine
- orange —> colourless colour change

Question 7

hydrogenation of alkenes

Answer 7

alkene + 180 heat & Ni catalyst —> alkane

Question 8

alkene –> alcohol

Answer 8

steam
phosphoric acid
e.g. produces ethanol from ethene

Question 9

alkene —> haloalkane

Answer 9

electrophilic addition
room temp
gaseous halogen halide (if liquid, then HX is bubbled through)

Question 10

why can alkenes undergo electrophilic addition?

Answer 10

double bond = high region of electron density that readily attracts electrophiles

Question 11

Marcownicoff’s rule

Answer 11

majority product = most stable, higher yield
carbocation is on the carbon attached to the most carbons to share its + charge.

Question 12

polymerisation environmental concerns

Answer 12

• many waster polymers are non-biodegradable & cause pollution as won’t decay naturally = kill marine life
• PVC recycling = hazardous (high chlorine content), burning PVC releases HCl(g) into environment

Question 13

Recycling polymers

Answer 13

1)decrease waste going to landfill
- sort by type
- chop into flakes
- wash & dry
- melted
- cut into pellets & used to make new products

2) feedstock recycling
- reclaim monomers from waste polymers
- reassemble products in crude oil refineries
- handles unwanted & unwashed polymers

3) Using waste polymers as fuel
- incinerate to produce heat
- generate steam
- turn turbine
- generate electricity

Question 14

Biodegradable polymers

Answer 14

• Broken down into biodegradable compounds (CO2 & H2O)
• made from starch & cellulose
• no toxic residues = compostable
• bio plastic replacing non-bio plastic

Question 15

photodegradable polymers

Answer 15

• oil-based
• bonds weaken through light absorption & degrade