Alcohols Flashcards
What is the general formula of alcohols?
CnH2n+1OH
How do you classify alcohols?
primary/secondary/tertiary depending on how many carbon atoms are directly attached to the carbon with the -OH bonded to it
What is fermentation used for?
making ethanol
What happens in the fermentation process?
an aqueous solution of plant sugar is converted into ethanol and carbon dioxide by living yeast cells
What is the equation and conditions for fermentation?
C6H12O6 —> 2C2H5OH + 2CO2
35C in aqueous solution with yeast under anaerobic conditions
Why does fermentation need to be carried out in anaerobic conditions?
the presence of oxygen would cause the ethanol to oxidise to ethanoic acid (vinegar)
Why can fermentation not be carried out at high temperatures?
because the yeast cannot survive and the enzyme it contains will be denatured
Why can fermentation not be carried out at lower temperatures?
the enzymes in yeast are not activated and the rate of reaction is too slow
What type of process is fermentation and what does it produce?
a batch process and produces a mixture of compounds
What happens in a batch process?
the reactants are mixed together and once the reaction is over the product is removed and the process repeats
How is the ethanol produced separated?
by fractional distillation of fermented products
What is fermentation used for?
make alcoholic drinks/bread/biofuel
Compare direct hydration with fermentation for making alcohols in industry
direct hydration-
-continuous process- cheap on manpower, expensive equipment and high energy use
-fast reaction
-pure product
-high yield
-uses ethene from crude oil which is a finite resource
fermentation-
-batch process- expensive on manpower, cheap equipment and low energy use
-slow reaction
-impure product
-low yield
-uses sugars which is a renewable resource
What is biofuel?
fuels made from plants or biomass
Why are biofuels classified as renewable?
the plants can be grown again quickly
What is a carbon neutral activity?
an activity that has no net annual carbon/greenhouse gas emissions to the atmosphere
Why is ethanol biofuel considered to be carbon neutral?
the amount of carbon dioxide made during ethanol combustion + the amount of carbon dioxide released by ethanol formation = amount of carbon dioxide removed from the atmosphere during photosynthesis
PHOTOSYNTHESIS-
6CO2 + 6H20 —-> C6H12O6 +6O2
6 moles of CO2 removed per 1 molecule of sugar
FERMENTATION-
C6H12O6 —-> 2C2H5OH +2CO2
COMBUSTION-
2C2H5OH + 6O2 —->4CO2 +6H2O
6 moles of of CO2 released during the fermentation and combustion of ethanol
Why might some people disagree with ethanol biofuel being carbon neutral?
the fermentation production and processing steps require energy, and this energy may involve the release of additional carbon dioxide (such as fractional distillation)
crops being grown for fermentation may be contributing to deforestation in order for more space, which releases the tree’s natural store of CO2
What is an elimination reaction?
where a small group of atoms breaks away from a larger molecule, not being replaced by anything else
What alcohols can undergo elimination reactions?
primary and secondary alcohols- NOT tertiary
as long as there is a carbon attached to the C-OH that also has a H bonded then it can
What do elimination reactions of alcohols produce?
alkenes and water
When do alcohols undergo elimination?
when they are heated with a suitable acid catalyst (such as concentrated phosphoric acid H3PO4 or concentrated sulphuric acid H2SO4
Why is it called a dehydration reaction?
water molecule is eliminated in the reaction
Draw the full exam mechanism for the dehydration reaction of ethanol
google to check is right but- lone pair on the oxygen in the OH attacks the H+, which makes it O+, so the covalent bond breaks between C-O leaving water molecule and a C+, so the H on the other C-H forms a C=C bond and a H+
When can there be more than one product in dehydration?
when its a secondary alcohol
Describe the type of reaction (not the mechanism) that dehydration is and it’s similarities to direct hydration
both are reversible reactions
alcohol ⇌ alkene + water (heat/acid catalyst)
alkene + steam ⇌ alcohol (300C/phosphoric acid/65000kPa)
dehydration is elimination
direct hydration is electrophilic addition
How can dehydration reactions be involved in addition polymerisation?
instead of doing fractional distillation of crude oil to make alkanes, then cracking them to get alkenes to be used in addition polymerisation
you can do dehydration of alcohols to make alkenes directly
