alcohols Flashcards
what general uses do alcohols have
scientific
medicinal
industrial
what are two ways alcohols can be produced
hydration or alkenes eg ethene in the presence of an acid catalyst
ethanol can be produced by fermentation of glucose
(also ns of halkanes with Aq oh-
Or reduction of aldehydes / ketones)
describe the process of hydration of alkenes
crude oil separated to get ethene
in aq phosphoric (H3PO4) acid
- H+ ion attacks double bond
- forms carbocation
- water molecule attaches to +ve C in the molecule
- bond between O and one of the Hs in the added water molecule gles to completely positive O
- forms alcohol and H+ ion. therefore acid is a catalyst
adv/disad of hydration (3/3)
ADV
faster
purer product
continuous process so cheaper manpower
DISADV
expensive tech needed
ethene is non renewable
high energy costs for pumping to produce high pressure
conditions for hydration of ethene
300°C
60 ATM
solid / conc p(v) acid
describe process of fermentation to produce ethanol
conditions
yeast anaerobically respire to form ethanol and CO2 from water and glucose
yeast
no air
temp between 30 and 40°C
explain the conditions of fermentation
no air
further reactions could occur eg ethanol oxidised to e.acid
temp
at lower temps reaction is too slow. at higher, enzymes denature and yeast die so reaction slows/stops
adv/disadv of fermentation (2/3)
ADV
1. renewable resource (sugar)
2. uses low level tech (cheap)
DISADV
1. batch process is slow and gives high production costs
2. ethanol made is impure, have to do f. distillation after
3. depletes land use for food growth
ethanol is can be used as a biofuel. what’s a biofuel
fuel produced over short time span from biomass which can be produced from plants or domestic biowaste
what’s carbon neutrality
an activity that has no net annual carbon emissions to the atmosphere
Ethanol produced from fermentation is a biofuel. why can it be argued that the use of it is carbon neutral?
CO2 given off when it is
- made as a product of resp in yeast and
- burnt
is taken in during ptts to make the glucose to use in the fermentation chamber
equations to show the carbon neutrality of combustion of ethanol
forming of glucose (ptts)
6CO2 + 6H2O -> glucose + 6O2
fermentation to produce ethanol
glucose -> 2CH3CH2OH + 2CO2
combustion
2 ethanol+ 6O2 -> 4CO2 + 6H2O
why is it not carbon neutral
energy needed to irrigate the plants
impure so f distillation of ethanol from reaction mixture
processing the fuel
transport
fermentation, the energy for processing, transportation, even the fertilizers used to grow plants
what is K2Cr2O7
an oxidising agent
Cr2O7 has a 2- charge btw
Gets reduced to Cr3+
partial oxidation of primary alcohols
- reagents
- product
- conditions
potassium dichromate and dilute sulfuric acid
forms an aldehyde and water
heat and distill off product immediately (by having heat be above aldehyde BP)
partial oxidation of primary alcohols: practical set up and observation
dichromate ion makes reaction mixture orange initially then gets rescued to Cr3+ ion which is green
look at set up and test yourself to draw it
full oxidation of primary alcohols:
reagent
product
conditions
potassium dichromate and sulfuric acid
c acid and water
heat under reflux
in this one the aldehyde is further oxidised from partial. so in eq do 2[O]
full oxidation of primary alcohols: practical set and observation
look at set up
Reflux: continually heatthe contents of the flask to allow reactions like the oxidationof primary alcohols to proceed all the way to the formation of carboxylic acids. The condenserhelps ensure the vapours condense and return to the flask for further heating.
oxidation of secondary alcohols
reagent
product
conditions
potassium dichromate and sulfuric acid
ketone and water
heat under reflux
why are tertiary alcohols not easily oxidised
No h on the C-oh
the method used to oxidise a primary alcohol determines what
explain
what product, aldehyde or c acid is obtained
if distilling off product, aldehyde
if under reflux, c acid
how can we distinguish between aldehyde or ketones (2)
why would we want to
tollens reagent
fehlings solution
you can know if you’ve got a primary or secondary alcohol by doing the distillation and the reflux for both unknowns
then doing the test for each product you get
the unknown that is positive for aldehyde must have been a primary alcohol
the unknown that isn’t must have produced a ketone so its a secondary alcohol
outline process of tollens reagent
( a reaction / test of aldehydes )
tollens is a mixture of aq ammonia and silver nitrate
it forms [Ah(NH3)2]+ complex ions
heat gently
aldehydes only are oxidised into a c acid. the silver ions are reduced to silver atoms. this forms a silver mirror coating the inside of the rest tube
aldehyde + 2Ag+ + water -> c acid + 2Ag + 2H+
outline process of fehlings
( test / reaction of aldehydes)
fehlings is Cu2+ ions
when heated gently it oxidises aldehydes to x acid. the ions are reduced to Cu2O which is a red precipitation
ketone + 2Cu2+ + 2water -> c acid + Cu2O + 4H+
