3.3 Organic Chemistry: .5 Alcohols

Question 1

what is the functional group of alcohols?

Answer 1

hydroxyl group

-C-OH

Question 2

in what ways can ethanol be made?

Answer 2

1. ) through fermentation
2. ) through catalytic hydration of ethene

Question 3

what is the eqaution for the fermentation reaction where ethanol is made?

Answer 3

C₆H₁₂C₆ → 2CH₃CH₂OH + 2CO₂

glucose → ethanol + carbon dioxide

Question 4

what are the key conditions for fermentation and state why each is used?

Answer 4

1. ) Sugar Solution:
   - to provide the glucose
2. ) 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)
3. ) Yeast
   - required as yeast contains the enzymes that break down the ethanol and speeds up the reaction without being used up itself (biological catalyst)
4. ) 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

Question 5

what is done to purify the ethanol made in fermentation?

what is this type of ethanol used for?

Answer 5

1. ) the yeast is filtered off
2. ) 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

Question 6

what is the eqaution for the catalytic hydration reaction of ethene?

Answer 6

CH₂=CH₂ + H₂O → CH₃CH₂OH

Question 7

what are the key conditions used in the catalytic hydration of ethene? state why each one is used

Answer 7

1. ) steam
   - this required as the reaction works by the addition of water (which you call hydration)
2. ) Catalyst (either conc. sulphuric acid or conc. phosphoric acid)
   - this is used as it speeds up the reaction but doesn’t get used up.

Question 8

explain (with a diagram of the mechanism) what happens in the hydration of ethene to make ethanol

Answer 8

1. ) -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.
2. ) -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)
3. ) -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!)

Question 9

what is another name for Propane-1,2,3-triol?

draw it out

Answer 9

glycerol

Question 10

compare the two ways of making ethanol (fermentation and catalytic hydration) in terms of rate, purity of product, process and raw materials used

Answer 10

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)

Question 11

what is a biofuel?

Answer 11

a fuel thats made from biological material thats recently died

Question 12

what are the advantages and disadvantages of using biofuels?

Answer 12

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

Question 13

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

Answer 13

Question 14

what are three types of alcohols and what are the difference between them?

Answer 14

• 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.

Question 15

what oxidising agent can you use to oxidise alcohols and what do you observe when this reaction takes place (also why does this happen)?

Answer 15

oxidising agent: acidified potassium dichromate(VI) K₂Cr₂O₇

observe a colour change of orange to green because the dicromate(VI) ion (Cr₂O₇^2-) is reduced to chromium (III) ion (Cr^3-)

Question 16

what do aldehydes have?

what is their suffix?

give an example with a diagram

Answer 16

Question 17

what do aldehydes have?

what is their suffix?

give an example with a diagram

Answer 17

Question 18

what do aldehydes have?

what is their suffix?

give an example with a diagram

Answer 18

Question 19

in the oxidation of alcohols what do we mean by oxidation?

Answer 19

the loss of hydrogen

Question 20

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?

Answer 20

products of this reaction is a

• aldehyde
• water

colour change:

orange to green

Question 21

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.

Answer 21

• this reaction happens in reflux (where there is excess K2Cr2O7)
• a carboxylic acid is made (ethanoic acid)

Question 22

what does heating under reflux mean and what apparatus is used?

Answer 22

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

Question 23

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?

Answer 23

products produce are:

a ketone (propanone)

water

colour change:

orange to green

Question 24

why are tertiary alcohols not easily oxidised?

Answer 24

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

Question 25

what is similar between the oxidation reaction between a primary alcohol and a seondary alcohol?

Answer 25

• they both lose two hydrogens
• they both forma double bond (C=O)
• both have a colour change of orange to green

Question 26

ways ro remember oxidation reactions

Answer 26

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

Question 27

in the dehydration of alcohols what reagents are used, what type of mechanism takes place and what are the general products?

Answer 27

reagents: hot conc. H2SO4/H3PO4
mechanism: elimination
products: alkenes and water

Question 28

show the reaction between ethanol and hot concentrated sulfuric acid

name this mechanism

Answer 28

this is an elimination reaction

Question 29

in the reaction of an alcohol with H2SO4/H3PO4 how would you seperate the chemicals to get the alkene?

Answer 29

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

Question 30

what are biofuels

Answer 30

biofuels is a fuel formed from biological material

Question 31

what is the functional group for aldehyde?

Answer 31

the aldehyde is at the end of the hydrocarbon chain

Question 32

what is the funtional group for a ketone?

Answer 32

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)

Question 33

what are the three types of reagents you can use to distinguish between and aldehyde and ketone

state what you observe

Answer 33

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

Question 34

what is the test for caboxylic acids?

Answer 34

you use sodium carbonate and the acid efferverces and the CO2 turns lime water milky