3.3 Organic Chemistry: .5 Alcohols Flashcards
what is the functional group of alcohols?
hydroxyl group
-C-OH
in what ways can ethanol be made?
- ) through fermentation
- ) through catalytic hydration of ethene
what is the eqaution for the fermentation reaction where ethanol is made?
C6H12C6 → 2CH3CH2OH + 2CO2
glucose → ethanol + carbon dioxide
what are the key conditions for fermentation and state why each is used?
- ) Sugar Solution:
- to provide the glucose - ) Absence of Air
- This is required becasue when ethanol is in the presence of oxygen (air) the substance can become oxidised to make ethanoic acid (vinegar) - ) Yeast
- required as yeast contains the enzymes that break down the ethanol and speeds up the reaction without being used up itself (biological catalyst) - ) 37 degrees C
- optimum temperature for this reaction. if it is too high then the enzymes will denature and if it is too loow the enzymes may move too slow and the yeast wont be as effective
what is done to purify the ethanol made in fermentation?
what is this type of ethanol used for?
- ) the yeast is filtered off
- ) the ethanol is seperated from the water by fractional distillation: ethanol boils at 78 degrees C whilst water boils at 100 degrees C so they are easily seperated
the ethanol from fermentation is used to make alcoholic drinks
what is the eqaution for the catalytic hydration reaction of ethene?
CH2=CH2 + H2O → CH3CH2OH
what are the key conditions used in the catalytic hydration of ethene? state why each one is used
- ) steam
- this required as the reaction works by the addition of water (which you call hydration) - ) Catalyst (either conc. sulphuric acid or conc. phosphoric acid)
- this is used as it speeds up the reaction but doesn’t get used up.
explain (with a diagram of the mechanism) what happens in the hydration of ethene to make ethanol
- ) -all of the hydrogen atoms in the acid (either phosporic acid or sulfuric acid) are partially positively charged because they are attracted to a very electronegative oxygen atom
- one of these hydrogens is strongly attracted to the carbon-carbon double bond.
- so this double bond breaks to make a bond with the hydrogen, forcing the the electrons in the hydrogen-oxygen bond down entirely onto the oxygen. - ) -The carbocation (carbonium ion) formed reacts with one of the lone pairs on a water molecule. (this makes sense as the oxygen atom in the water molecule is partially negative bc of its high electronegativity)
- ) -one of the hydrogens on the oxygen is removed by reaction with the acid ion (either the phosophoric or sulfuric acid as they had lost a hydrogen in the first step) formed in the first step.
- Here the acid is regenerated (this is why it is a catalyst!)
what is another name for Propane-1,2,3-triol?
draw it out
glycerol
compare the two ways of making ethanol (fermentation and catalytic hydration) in terms of rate, purity of product, process and raw materials used
RATE:
catalytic hydration of ethene- fast
fermentation- slow
PURITY OF PRODUCT:
catalytic hydration of ethene- pure
fermentation- impure
PROCESS:
catalytic hydration of ethene- batch
fermentation- continuous
RAW MATERIAL USED:
catalytic hydration of ethene- crude oil (non renewable)
fermentation- sugar (renewable)
what is a biofuel?
a fuel thats made from biological material thats recently died
what are the advantages and disadvantages of using biofuels?
ADV:
- biofuels are renewable energy sources
- unlike fossil fuels, biofuels wont run out, so they’re more sustainable
- biofules are usually classes as carbon neutral bc they produce CO2 that the plant absorbed while growing
DIS:
- petrol car egines would have to be modified to use fuels with high ethanol concentrations
- when you use land to grow crops for fuel, that land cant be used to grow food so if countries started using land to grow biofuel crops instead of food, they may be unabl to feed everyone in the country
write equations to support the statement that ethanol produced by fermentation is a carbon neutral fuel and give reasons why this statement is not valid
what are three types of alcohols and what are the difference between them?
- the three types of alcohols are: primary, secondary and tertiary.
- the differences are:
Primary alcohols have one carbon chain coming of the functional group and can be oxidised to aldehydes which can be further oxidised to carboxylic acids
Secondary alcohols have two carbon chains coming of the functional group and can be oxidised to ketones.
Tertiary alcohols have three carbon chains coming of the functional group and are not easily oxidised.
what oxidising agent can you use to oxidise alcohols and what do you observe when this reaction takes place (also why does this happen)?
oxidising agent: acidified potassium dichromate(VI) K2Cr2O7
observe a colour change of orange to green because the dicromate(VI) ion (Cr2O72-) is reduced to chromium (III) ion (Cr3-)
what do aldehydes have?
what is their suffix?
give an example with a diagram
what do aldehydes have?
what is their suffix?
give an example with a diagram
what do aldehydes have?
what is their suffix?
give an example with a diagram
in the oxidation of alcohols what do we mean by oxidation?
the loss of hydrogen
write a displayed eqaution for the reaction between a primary alcohol (ethanol) and potassium dicromate (VII)
state what is formed
what is the colour change for this reaction?
products of this reaction is a
- aldehyde
- water
colour change:
orange to green
write the eqaution (displayed) for the reaction where an aldehyde (ethanal) is further oxidised.
State what process this reaction happens under
what products are made.
- this reaction happens in reflux (where there is excess K2Cr2O7)
- a carboxylic acid is made (ethanoic acid)
what does heating under reflux mean and what apparatus is used?
heating under reflux means:
- you increase the temperature of an organic reaction without losing volatile solvents, reactants or products
- an vaporised compounds cool, condense and drip back into the reaction mixture
- so the aldehyde stays in the reactiion mixture and is oxidised to carboxylic acid
The apparatus used for this is:
- a liebig condenser that is conected to a round bottomed flask
- heat is passed through the flask which has anti-bumping granules to make boiling smoother
write the eqaution (displayed) for the oxidation reaction of a secondary alcohol (propan-2-ol)
state what prducts are produced
what is the colour change for this reaction?
products produce are:
a ketone (propanone)
water
colour change:
orange to green
why are tertiary alcohols not easily oxidised?
tertiary alcohols are not easily oxidised because:
-they dont have two hydrogens on the functional group
the oxidation reaction would need a C-C bond to break rather than a C-H bond
what is similar between the oxidation reaction between a primary alcohol and a seondary alcohol?
- they both lose two hydrogens
- they both forma double bond (C=O)
- both have a colour change of orange to green
ways ro remember oxidation reactions
1.)Primary alcohols produce aldehydes
PAH
P= primary alcohol A=Aldehyde H=H2O
2.) Primary alcohols can also produce carboxylic acid in reflux
PAC
P= primary alcohol to A=Aldehyde to C=carboxylic acid
3.) Secondary Alcohols produce ketones
how SK is that?
S=secondary K=ketones
in the dehydration of alcohols what reagents are used, what type of mechanism takes place and what are the general products?
reagents: hot conc. H2SO4/H3PO4
mechanism: elimination
products: alkenes and water
show the reaction between ethanol and hot concentrated sulfuric acid
name this mechanism
this is an elimination reaction
in the reaction of an alcohol with H2SO4/H3PO4 how would you seperate the chemicals to get the alkene?
stage 1- distillation:
add the acid to a round-bottom flask containing the alcohol and mix the solution and add 2-3 carborundum boiling chips
the mixture should be heated to the boiling point of the alkene using a water bath or electric heater
the chemicals with a boiling point similar to the alkene will evaporate out of the flask into the condenser which turns it into liquid
the product can then be collected in a cooled flask
stage 2- seperation
the product collected after distillation will still contain impurities
transfer the product mixture to a seperating funnel and add water to dissolve water soluble impurities and create an aqueous solution
allow the mixture to settle into layers then drain the aqueous lower layer, leaving the impure cyclohexane
stage 3- purification
drain the cyclohexene into a round-bottomed flask
add anhydrous CaCl2 (a drying agent) and stopper the flask, let the mixture dry for at least 20 minutes with occasional swirling
the cyclohexene will still have small amounts of impurities so distil the mixture one last time
what are biofuels
biofuels is a fuel formed from biological material
what is the functional group for aldehyde?
the aldehyde is at the end of the hydrocarbon chain
what is the funtional group for a ketone?
ketones dont have a Hydrogen bonded to it, thats why ketones can not be further oxdised (oxidation is loss of electrons but also loss of H+ ions)
what are the three types of reagents you can use to distinguish between and aldehyde and ketone
state what you observe
1.) Pottasium dichromate (K2Cr2O7) and H2SO4
aldehyde is oxidised so colour change of orange to green
ketone is not oxidised so no colour change
2.) Tollen’s reagent
aldehyde is oxidised so colour change of colourless solution to silver mirror
ketone is not oxidised so no colour change
3.) Fehling’s solution (Benedicts solution)
Aldehyde is oxidised so colour change of blue solution to brick red ppt
ketone is not oxidised so no colour change
what is the test for caboxylic acids?
you use sodium carbonate and the acid efferverces and the CO2 turns lime water milky
