Organic chemistry

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C8.12 Producing ethanol by fermentation
Fermentation is a chemical reaction that turns sugar into alcohol using  yeast.  Yeast is a type of fungus that contains enzymes.  Enzymes are chemicals made by living things which speed up reactions (biological catalysts).
Yeast cells feed on the sugar and reproduce and anaerobic respiration (without oxygen) takes place.  The best temperature for the yeast is about 37oC.  At lower temperatures yeast does not grow well and at higher temperatures the enzymes are denatured (decompose).



glucose -----------> ethanol + carbon dioxide
(a sugar)              (an alcohol)
(a carbohydrate)
C6H12O6(aq) -----> 2C2H5OH(l) + 2CO2(g)

Ethanol (bp =78oC) is separated from water (bp = 100oC) by fractional distillation as the boiling points are close together.



C8.13 Producing ethanol by hydration of ethene
Ethanol is also made by reacting ethene with water (hydration).  This is an adition reaction.  The conditions are 300oC, 60 atmospheres pressure and a catalyst of phosphoric acid, H3PO4.  The conditions favour the products in the equilibrium reaction below.
C2H4(g) + H2O(g) <---> C2H5OH(g)

C8.14 Factors affecting the choice of method to manufacture of ethanol
Ethanol is made by fermentation or by hydration.
If there is good availability of  cane sugar then fermentation is a good method.  This is the case is Brazil where ethanol is used in place of petrol for cars.  Fermentation is also the preferred method when the alcohol made is to go into alcoholic drinks.  Hydration is a better method where ethene from crude oil is plentiful e.g. in the UK or where the alcohol is for industrial uses such as in solvents.

C8.15 The amounts of ethanol present in various drinks

Different drinks have different strengths
All alcoholic drinks contain pure alcohol (ethanol) in different amounts.  The strength of the alcoholic drink is shown on the label by a number followed by 'Alcohol % vol', '% vol' or '% ABV.'  The higher the percentage, the stronger the drink.

For example, a bottle of beer may may have '3.5% ABV' written on the label - this means that 3.5% of the drink is pure alcohol.

One way of comparing the amount of alcohol in different types of drinks is using ‘units’. One unit is the same as 1cl of pure alcohol.  Each of the following contains one unit.
(ABV = alcohol by volume)

   
Wine A small glass of wine = 1 UNIT
(9% ABV, but many wines are 11 or 12% ABV)
Beer Half pint of ordinary strength lager/beer/cider = 1 UNIT
(3.5% ABV, but many bottled beers are 4-5% ABV)
Spirits A 25ml pub measure of spirit = 1 UNIT
(40% ABV)
Alcopops A 330 ml bottle of alcopops  = 1.7 UNITs
(5% ABV)

Watch Out!!! - Alcopops often contain more alcohol than many beers, lagers or ciders.

They have been designed to hide the naturally strong alcoholic taste of traditional drinks.  Because they taste fruity and are easier to drink doesn't mean they will have less effect - they will have the same if not more effect as other alcoholic drinks
   
There are guidelines on how many units of alcohol an adult can drink a day before risking their health. These are 2-3 units a day for women and 3-4 for men. However, these guidelines do not apply to young people. Adult bodies react differently to alcohol and the adult liver is larger.

It takes about 1 hour for the adult body to get rid of 1 unit of alcohol.  This may be slower in young people because of differences in physical maturity.

above section adapted from http://www.careincrisis.org.uk/whoschoosing/alcohol/strength.htm

Complete a table of actual named drinks and their alcohol content.
C8.16 Social issues and possible harmful effects of ethanol in alcoholic drinks

One drink can effect you
Alcohol enters the bloodstream within minutes of being drunk and is carried to all parts of the body including the brain.  The first effect of alcohol is to change a persons mood.  It is a depressant drug - it depresses (or slows down) the way the body works.  It switches off the part of the brain which controls judgement, making people do things they may not normally do.

How alcohol affects the body depends upon things such as;

  • body weight
  • male or female
  • how quickly it is drunk
  • length of time from last meal
  • if taken with another drug

The same amount of alcohol may have different effects upon different people.  Young people especially need to be careful because their bodies may not be fully ready to deal with alcohol in the same way as an adults.  This is partly due to the smaller body size and partly because a young persons liver is not as good at dealing with the toxic substances found in alcohol.

In small amounts alcohol may produce feelings of relaxation, fun and laughter.  It can make it easier for people to enjoy the company of others, and for a short time it may help people forget about things that are worrying them.

However, in larger amounts alcohol may make some people want to fight and argue.  People drinking alcohol may become uncoordinated and lose control, may become sleepy, and may (if they drink a lot) cause serious harm to themselves and possibly others.

Short Term Effects Long Term Effects
  • vomiting
  • headache
  • accidents
  • getting into fights
  • losing control of one's actions
  • death through alcohol poisoning
  • attempted suicide
  • family arguments
  • dehydration
  • damage to the liver, stomach, heart and/or brain
  • loss of memory
  • put on weight
  • changes in personality
  • become dependant - need it all the time
  • unable to digest food properly

Add to the short and long term columns above using the information here.
Sort the effects into social and physical problems.
C8.17 Industrial methylated spirit
A mixture of 95% ethanol and 5% water is used in hospitals and else where as a solvent.  This could be drunk in alcoholic drinks but normal alcoholic drinks are taxed so the sale of this mixture is restricted.  A similar but much cheaper mixture can be sold as a solvent or fuel if methanol is added.  This is called industrial methylated spirits.  Methanol is like ethanol but is poisonous and can cause blindness so industrial methylated spirits cannot be put into alcoholic drinks and can be sold cheaply without tax.



C8.18 The use of ethanol as a solvent and as a fuel
Ethanol is a good solvent used in cosmetics, toiletries, thinners for laquers and for printing inks.  It evaporates quickly leaving the product in place.  It burns very cleanly and has been mixed with petrol to fuel cars.  Petrol which contains 10% ethanol can be used in a car without altering the engine.
2C2H5OH(l) + 6O2(g) -----> 4CO2(g) + 6H2O(l)

C8.19 The oxidation of ethanol to form ethanoic acid
Oxidation is a reaction with oxygen.  Ethanol in wine for example will react with oxygen in the air to form ethanoic acid.  This is assisted by microbes and is the cause of wine going sour if the top is left off.
ethanol + oxygen -----> ethanoic acid + water
 C2H5OH(l) + O2(g) -----> CH3COOH(aq) + H20(l)
This reaction is quicker if an oxidising agent such as potassium dichromate (VI), K2Cr2O7 is used.  This is orange in colour but in the presence of sulphuric acid it oxidises ethanol to ethanoic acid and turns green/blue in the process.

C8.20 Ethanoic acid and ethanoate salts
Ethanoic acid is a typical acid with one hydrogen atom that can be replaced by a metal.  The result is a type of salt called an ethanoate.
Ethanoic acid is a weak acid so universal indicator is likely to be orange showing a pH of about 5.  
With metals a salt and hydrogen are formed.   E.g.
magnesium + ethanoic acid -----> magnesium ethanoate + hydrogen
Mg(s) + 2CH3COOH(aq) -----> (CH3COO)2Mg(aq) + H2(g)
With bases (metal oxides or hydroxides) it forms a salt and water. E.g.
sodium hydroxide + ethanoic acid -----> sodium ethanoate + water
NaOH(aq) + CH3COOH(aq) -----> CH3COONa(aq) +H2O(l)
With carbonates a salt water and carbon dioxide are formed.  Eg.
copper carbonate + ethanoic acid ---> copper ethanoate + water + carbon dioxide
CuCO3(s) + 2CH3COOH(aq) -----> (CH3COO)2Cu(aq) + H2O(l) + CO2(g)
Describe the reactions of ethanoic acid with calcium, Ca; magnesium oxide, MgO; and potassium carbonate, K2CO3.

C8.21 Ethanoic acid in vinegar
Vinegar is a dilute solution of ethanoic acid in water.  Vinegar is used to add a sour tasting flavour to food.  It is very difficult for bacteria to grow in ethanoic acid so vinegar is also used as a preservative for food.
Make one list of foods in which vinegar is used mainly to provide a flavour and a second in which vinegar is used mainly as a preservative.  Try here for some tips.
C8.22 The reaction of ethanol with ethanoic acid
Ethanol and ethanoic acid react together in the presence of concentrated sulphuric acid to for ethyl ethanoate.  This is an example of an ester.  Warming speeds up the reaction which is know as esterification. 
ethanol + ethanoic acid ---> ethyl ethanoate + water
 C2H5OH(l) + CH3COOH(aq) ----> CH3COOC2H5(aq) + H2O(l)

C8.23 The smell and uses of esters

Apple

Ester smells

The smells of fruits are due to the presence of complicated mixtures of chemicals, (not always just esters) rather than solely one ester, but individual esters are often important components in this.

 Pear




Esters of aromatic acids also have characteristic smells

grapes

Though the size of the molecules varies, it seems that the presence of the COO group is vital to the kind of smell.
Above adapted from http://www.tlchm.bris.ac.uk/motm/ethylacetate/ethylh.htm
Uses of esters include solvents, flavourings and perfumes.


C8.24 Homologous series
 A homologous series is a set of organic compounds in which one member of the set differs from the next only by the addition or loss of a -CH2- group. Each member of a series has similar properties.  E.g.
alkanes: H-CH2-H, H-CH2-CH2-H etc.
alkenes: H-CH=CH-H, H-CH=CH-CH2-H etc.
alcohols: HO-CH2-H, HO-CH2-CH2-H etc
carboxylic acid: HOOC-H, HOOC-CH2-H etc.
C8. 25 The names, formulae and structures of homologous series
alkanes

name formula structure
methane CH4         H
         |
    H-C-H
         |
        H
ethane C2H6         H H
         |   |
    H-C-C-H
         |   |
        H H
propane C3H8         H H H
         |   |   |
    H-C-C-C-H
         |   |   |
        H H H
butane C4H10         H H H H
         |   |   |   |
    H-C-C-C-C-H
         |   |   |   |
        H H H H

alkenes

name formula structure
ethene C2H4         H  H
         |    |
    H-C=C-H
propene C3H6         H  H H
         |    |   |
    H-C=C-C-H
                 |
                H
butene C4H8         H  H H H
         |    |   |   |
    H-C=C-C-C-H
                 |   |
                H H

alcohols

name formula structure
methanol CH3OH         H
         |
    H-C-O-H
         |
        H
ethanol C2H5OH         H H
         |   |
    H-C-C-O-H
         |   |
        H H
propanol C3H7OH         H H H
         |   |   |
    H-C-C-C-O-H
         |   |   |
        H H H
butanol C4H9OH         H H H H
         |   |   |   |
    H-C-C-C-C-O-H
         |   |   |   |
        H H H H

carboxylic acids

name formula structure
methanoic acid HCOOH         O-H
         |
    H-C=O
         
        
ethanoic acid CH3COOH         H O-H
         |   |
    H-C-C=O
         |   
        H 
propanoic acid C2H5COOH         H H O-H
         |   |   |
    H-C-C-C=O
         |   |   
        H H 
butanoic acid C3H7COOH         H H H O-H
         |   |   |   |
    H-C-C-C-C=O
         |   |   |   
        H H H 


C8.26 The variation in physical properties in a homologous series
 The substance is a homologous series show a gradual change in properties such as boiling point.  E.g. The boiling points of the alkanes get higher as the size of the molecule increases. The increase in boiling points becomes less as the molecules become larger.

alkanes

name formula boiling point / oC
methane CH4 -164
ethane C2H6 -87
propane C3H8 -42
butane C4H10 0
pentane C5H12 36
hexane C6H14 69

 Plot boiling point against number of carbon atoms for the alkanes above.
C8.27 The similar chemical properties of alcohols
 All alcohols have similar chemical reactions in that they undergo combustion and take part in esterification.
methanol + oxygen ----> carbon dioxide + water
2CH3OH(l) + 3O2(g) ----> 2CO2(g) + 4H2O(l)
Write equations to show the combustion of ethanol, propanol and butanol.
methanol + ethanoic acid ----> methyl ethanoate +water
CH3OH(l) + CH3COOH(l) ----> CH3COOCH3(l) + H2O(l)
Write equations to show ethanoic acid reacting with ethanol, propanol and butanol.

C8.28 The formulae and structures of esters
An ester is formed from an alcohol and a carboxylic acid.
The names have two parts.  An alcohol part and an acid part.
The alcohol part - the first part of the name (alkyl) is based on the alcohol.
methanol - methyl 
ethanol - ethyl
propanol - propyl
butanol - butyl
The acid part - the second part of the name is based on the acid.
methanoic acid - methanoate
ethanoic acid - ethanoate
propanoic acid - propanoate
butanoic acid - butanoate
So the ester formed from methanol and methanoic acid is methyl methanoate.
Name the esters formed from ethanol and methanoic acid, propanol and butanoic acid, butanol and ethanoic acid.
Name the alcohols and acids needed to make ethyl ethanoate, methyl butanoate, and propyl ethanoate.

The formula of an ester can be written by writing the formula of the acid and replacing the acidic hydrogen with an alkyl group.  E.g.
for propanoic acid and ethanol make ethyl propanoate
C2H5COOH + C2H5OH            C2H5COOC2H5

Write the formulae of ethyl ethanoate, methyl butanoate, propyl ethanoate, ethyl methanoate, propyl butanoate and butyl ethanoate.

To draw the structure of an ester start with the structure of the acid used and draw the alkyl group in place of the acidic hydrogen.  E.g. for ethyl propanaoate
Structure of propanoic acid is
        H H O-H
         |   |   |
    H-C-C-C=O
         |   |   
        H H 
Structure of ethyl propanoate is
                         H H
                          |   |
        H H O------C-C-H
         |   |   |         |    |
    H-C-C-C=O  H  H
         |   |   
        H H 
Draw the structures of ethyl ethanoate, methyl butanoate, propyl ethanoate, ethyl methanoate, propyl butanoate and butyl ethanoate.