C7: Further Chemistry

C7.2 Alcohols, carboxylic acids and esters

Organic Chemistry

Organic chemistry is a sub-discipline in chemistry that involves the scientific study of the structure, properties and reactions of organic materials and compounds.

Meeting the Alkanes

The alkanes are hydrocarbons, containing only hydrogen and carbon

The Alkanes

Methane CH4

Ethane C2H6

Propane C3H8

Butane C4H10

Why do we use alkanes?

Burning alkanes

If there is plenty of air, ie enough oxygen:

Methane + Oxygen Carbon dioxide + Water

CH4 + 2O2 CO2 + 2H20

Did you remember state symbols?

(g) (g) (g) (g)Can you write the balanced symbol

equation?

Alkanes and Aqueous Reagents

Alkanes are unreactive towards aqueous reagents because they contain only C—C and C—H bonds, which are difficult to break and therefore unreactive

C C CH

H

H

H

H

H

HH

Functional Groups

C CH

H

H

H

H HHO H

EthaneEthanol

All of the characteristic properties of alcohols are due to the presence of this functional group.

Can you give the molecular formula, structural formula, stick diagram for methanol and

ethanol?

Why do we need methanol and

ethanol?

Uses of alcoholsMethanol Ethanol

Chemical feedstock Fuel

Manufacture of cosmetics Solvent

CH3OH C2H5OH

Burning Alcohols in Air1. Can you write out the word equation for the combustion of

ethanol in air.2. Write out the balanced symbol equation

3. Don’t forget state symbols

Ethanol + Oxygen Water + Carbon dioxideC2H5OH + 3O2 3H20 + 2CO2(l) (g)(g) (g)

Alcohols burn in air to produce carbon dioxide and water because of the presence of a hydrocarbon chain

Why have I been using methanol

and ethanol for the demonstrations?

CCH

H

H

HH

O H

CCH

H

H

H

CCH

H

H

H

CCH

H

H

H

C

H

H

H O HMethanol

Octanol

The longer the hydrocarbon the stronger the intermolecular forces and therefore the higher the boiling point.Longer hydrocarbons are also less soluble in water as they behave more like an alkane and so float on top of water due to their low density

Physical Properties

Reactions with Sodium

Remember this? Sodium with water

Alcohols- Sodium sinks in alcohol and doesn’t melt, it will steadily give off hydrogen

Alkanes- Do not react with Sodium

Sodium with alcohol

Quick Quiz so far

1. Draw the structural formula for butanol2. Write the molecular formula for butanol3. Draw the structural formula for hexane4. Write the molecular formula for hexane5. Write the molecular formula for an alkane with 25

carbon atoms.6. How many bonds does oxygen make in methanol?7. Give an example of a use for ethanol8. Give an example of a use for methanol

1. Butanol2. C4H10O3. Hexane4. C6H14

5. C25H52

6. 27. Fuel/feedstock for synthesis/solvent/used in

perfume8. Solvent, antifreeze, feedstock for adhesives

and plastics

How do we make ethanol?

• What process do we use? It will be used in home brewing

• Fermentation is a key process for obtaining ethanol. It is relatively cheap and requires wheat or beet sugar.

• The process involves the anaerobic respiration of yeast at temperatures between 20 and 40°C and at pH 7.

Why is there a limit on the strength of alcohol that can be

made?

Key

Sugar

Ethanol

XMaking Alcohol

When the ethanol concentration gets too high it kills off the yeast cells

So how do we make stronger alcohol?

How do we obtain a concentrated solution?

• Ethanol has a different boiling point to water. We can therefore separate water and ethanol using distillation.

Give it a thoughtCan you balance this equation?

C6H12O6 → CH3CH2OH+ CO2

C6H12O6 → 2 CH3CH2OH+ 2 CO2

Can you name the

chemicals?

Other ways to make ethanol

Genetically modified E. coli bacteria can be used to convert waste biomass from a range of sources into ethanol

Optimum conditions:

Temperature remain between 25-37oC

Optimum pH level needs to remain constant

Other ways to make ethanol

They introduce new genes into the E.coli bacteria allowing it to digest all the sugars in the biomass and covert them into ethanol. Therefore we can use a wide range of biomass to make ethanol rather than staying as waste eg corn stalks.

Feedstock

Linking alkanes and alcohol

It is also possible to convert ethane into ethanol

Crude Oil undergoes fractional distillation

Long chain hydrocarbons (alkanes) are vaporised then cracked using a catalyst and heat

The molecules are purified using fractional distillation producing ethene

Ethene is then reacted with steam, at a high temperature and with a catalyst to produce ethanol An

y un

reac

ted

prod

ucts

can

be

recy

cled

and

fed

thro

ugh

the

syst

em a

gain

Write out the Symbol Equation

Ethene + Steam EthanolC2H4 + H20 C2H5OH

(g) (g) (g)

The UK is the world's largest producer of synthetic ethanol

Why is this not a good

fact?

4. Make a table listing the advantages and disadvantages of each method of producing ethanol.

Advantage Disadvantage

Fermentation renewable feedstocks, which include waste materials

maximum concentration of ethanol 15%

Biotechnology uses feedstocks that cannot be used in traditional fermentation, reducing waste; produces higher concentrations of ethanol

new technology still in development

Chemical synthesis

production of high concentrations of ethanol; 100% atom economy and high yields

feedstock non-renewable

Tackling the 6 marker

Which method do you think has the largest impact on the environment? Give reasons for your answer.

The Alkanes

C

H

HH H

C CH

H

H

H

H H C C C CH H H

H H H

H

HH H

C C CH

H

H

H

H

H

HH

• Make models with molymods

C CH

H

H

H

H O H

C

H

HH O H

C CH

H

H

H

H O HC CH

H

H

H

C CH

H

H

H

C CH

H

H

H