Topic 3.3 - Alkenes and Alcohols Flashcards
(22 cards)
What are alkenes?
- Unsaturated hydrocarbons
- C=C > high electron density
> quite reactive
What is the test for alkenes?
What is the result?
Test: Bromine water
Result: Orange > colourless
Happens by electrophilic addition
What are electrophiles?
- Electron pair acceptors
- Positively charged ions
- Polar molecules
What are the four substances react with alkenes in electrophilic addition?
- Br2
- HBr
- H2O
- Concentrated H2SO4
How does the double bond on an alkenes from a dipole-dipole in Br2?
Electron dense double bond repels electrons in Br-Br, inducing a dipole-dipole
Define monomer
Small molecules that can join together to make polymers
Define polymer
A long chained molecule formed of small repeating units (monomers) join together
Define addition polymerisation
Formation of polymers (long chain molecules) by lots of monomers (small alkenes) joining together
How do you name a polymer?
Poly(name of monomer)
Whyare addition polymers unreactive?
Give five reasons
- Chemically inert
- Strong covalent bonds
- Saturated
- Non-polar
-Strong, rigid
What is poly(chloroethene) (PVC)?
What are the properties?
What are its uses?
- During manufacture, plasticisers are added to make product more flexible
- Reduces strength of intermolecular forces between chains so the chains can slide over each other (rigid)
- Hard, brittle and waterproof
- Used for: electrical cable insulators
flooring tiles
clothing
What is the substance that reacts with alkenes in elimination reactions?
Concentrated H2SO4
What is distillation used for?
Separates organic compounds with different boiling points
What are the two ways of forming ethanol?
- Fermentation of yeast
- Hydrating ethene
How is ethanol formed from the fermentation of ethene?
What is the equation?
What are the conditions?
- Fermentation: Exothermic reaction
: Glucose > ethanol + carbon dioxide
: C6H12O6 (aq) > 2CH3CH2OH (aq) + 2CO2 (g) - Conditions: Yeast (produces enzymes which convert glucose into ethanol and carbon dioxide)
: Anaerobic environment (no oxygen)
: Warm environment
: Temperature (30•C - 40•C)
Why does producing ethanol from fermentation of yeast take time?
Ethanol once made, needs to be purified by distillation
How is ethanol formed from the hydration of ethene?
What is the equation?
What are the conditions?
- Ethene comes form cracking heavy fractions of crude oil
- CH2CH2 (g) + H2O (g) > CH3CH2OH (g)
- Conditions: Excess steam
: High temperature (300•C)
: High pressure (60 atm)
: Concentrated phosphoric acid catalyst (H3PO4) - Reversible reaction = yield is low
What are the advantages and disadvantages of creating ethanol from fermentation?
Advantages:
- Cheap equipment
- Renewable resource (sugars from plants)
Disadvantages:
- Impure product (further purification by fractional distillation)
- Time consuming because it is a broken up process
- High labour costs
What are the advantages and disadvantages of creating ethanol from hydrating ethene?
Advantages:
- Very quick process
- Pure product
- Continuous process
- Low labour costs
Disadvantages:
- Expensive equipment
- High energy costs (high temperature / high pressure)
- Finite resource (ethene from oil)
Define biofuel
A fuel that is made from biological material that has recently died
E.g. ethanol
What are the advantages and disadvantages of using ethanol as a fuel?
Advantages:
- Renewable energy source (more sustainable)
- Carbon neutral (releases same amount of carbon dioxide when burned as was taken in for photosynthesis)
Disadvantages:
- Ethical issues (land used to grow crops for fuel means less land is used to grow crops for food)
- Deforestation for space on land
- Trees often burnt, releasing carbon dioxide
- Fertilisers used to increase biofuel crop production (pollute waterways)
What are the three equations to show production of ethanol is carbon neutral?
Photosynthesis:
6CO2 + 6H2O > 6O2 + C6H12O6
Fermentation:
C6H12O6 > 2CH3CH2OH + 2CO2
Combustion:
2CH3CH2OH + 6O2 > 6H2O + 4CO2
