Chapter 13 Key Concepts Flashcards
What’s an alkene
An unsaturated hydrocarbon containing a CC double bond which comprises of a pi bond and a sigma bond. Pi bond locks the 2 C in position and prevents them rotating.
*contrastingly in Alkanes,rotation is possible around every atom
Trigonal planar with bond angle 120 around the CC
*double bond is 1 CNC
General formula CnH2n
*doesn’t count for cycloalkenes and alkenes with more than one double bond
CIP rules
each group is given a priority. The larger the proton number the higher the priority
- higher priorities across from each other - E
- higher priorities on the same side -Z
Why are alkenes more reactive than Alkanes?
The Pi bond has a lower bond enthalpy at 265kjmol than sigmas 347kjmol is Pi is broken more readily. Pi bond is also more exposed than the sigma bond in the CC db, those two combined means alkenes go theory e add more easily
Markownikoffs Rule
Hydrogen attaches itself to the Carbon with the most Hydrogen
The major project will be the one with the most stable carbocation
Why does stability increase from Primary to Tertiary Carbocation?
Each alkyl group donates and pushes electrons to the towards the positive charge on the carbocation
- positive charge is spread over the alkyl groups
- more alkyl attached to the Positively charged carbon means the charge is spread out more making the ion more stable
Uses of poly(Ethene)
LDPE -branched chains -little strength but flexible plastics for plastic films and plastic bags HDPE -linear chains -gives the plastic some strength -use for children's toys -Detergent bottles -Waterpipes
Uses of poly(chloroethene) aka pvc
Used for making flexible or rigid polymers
- pipes
- films and sheeting
- ducts and profiles
- insulation and cable sheeting
- bottles
- flooring
- fabric treatment
- moulded articles
Uses of poly(propene)
Children's toys Packing crates Guttering uPVC windows Fibre for ropes
Uses of poly(phenylethene/styrene)
Packaging material
Food trays and cups
*has very good insulating properties
Uses of poly(tetrafluoroethene) aka PTFE aka Teflon
Used as coating for non stick pans
Permeable membrane for clothing and shoes
Cable insulation
Pros of polymers
Readily available
Cheap to buy
More convenient than glass bottles, paper bags etc
Not reactive means suitable for storing food and chemicals safely
Recycling
Sort plastic bottles using their resin identification code
Chop them into flakes
Wash
Dry
Melt
Cut into pellets
Then used by manufacturer to make new products
recycling reduces environmental impact by
- conserving finite fossil fuels
- decreasing amount of waste going to landfill
HOWEVER mixed polymers renders product useless
Recycling
PVC recycling
- disposing of PVC is hazardous cuz high chlorine content ad range of additives in the polymer
- dumping isn’t sustainable
- burning releases corrosive gas HCl and other pollutants like dioxins
-before we used to grind and reuse PVC to make diff products
Now we use solvents to dissolve the polymer. Recover high grade PVC by ppt from the solvent and reuse solvent
Recycling
Using waste polymers as fuels
For when the polymer is difficult to recycle
- the polymer is made from natural gas/petroleum so it has a high energy stored value
- waste polymers are burnt to make heat, making steam, turns a turnbine and makes electricity
Eg in Sheffield. They use the electricity for the National grid and to heat buildings across the city centre
Recycling
Feedstock recycling and the advantages
The products of this process can then me used as raw materials for the production of new polymers
-major advantage is it can handle unsorted and unwashed polymers
