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Doc Brown's GCSE/IGCSE/O Level KS4 science–CHEMISTRY Revision Notes

Oil, useful products, environmental problems, introduction to organic chemistry

9. Alcohols , Ethanol, Properties, Reactions and Uses, Biofuels

What we call 'alcohol' actually has the proper chemical name ethanol and belongs to a group of organic molecules called alcohols? How do we make ethanol? Why has it been manufactured for thousands of years? How is ethanol made in industry? What is ethanol used for? All of these questions are answered below!

Index of KS4 Science GCSE/IGCSE Chemistry Oil & Organic Chemistry Pages: 1. Fossil Fuels : 2. Fractional distillation of crude oil & uses of fractions : 3. ALKANES – saturated hydrocarbons and combustion : 4. Pollution, carbon monoxide, nitrogen oxides, what makes a good fuel?, climate change–global warming : 5. Alkenes – unsaturated hydrocarbons : 6. Cracking – a problem of supply and demand, other products : 7. Polymers, plastics, uses and problems : 8. Introduction to Organic Chemistry – Why so many series of organic compounds? : 9. Alcohols – Ethanol – properties, reactions, biofuels : 10. Carboxylic acids and esters : 11. Condensation polymers, Nylon & Terylene, comparing thermoplastics, fibres and thermosets : 12. Natural Molecules – carbohydrates – sugars – starch : 13. Amino acids, proteins, enzymes & chromatography : 14. Oils, fats, margarine and soaps : 15. Vitamins, drugs–analgesic medicines & food additives and aspects of cooking chemistry! : 16. Ozone, CFC's and free radicals : 17. Extra notes, ideas and links on Global Warming and Climate Change : Multiple Choice and Gap–Fill Quizzes: m/c QUIZ on Oil Products (GCSE/IGCSE easier–foundation–level) : m/c QUIZ on Oil Products (GCSE/IGCSE harder–higher–level) : IGCSE/GCSE m/c QUIZ on other Aspects of Organic Chemistry : and 3 Easy linked GCSE/IGCSE Oil Products word–fill worksheets

9. What is ethanol and how can we make it?

The 'alcohol' of the homologous series of alcohols!

What we call alcohol in everyday life is a substance whose chemical name is ethanol.  Ethanol is just one member of a family of substances called alcohols which have a C–OH functional group in their structure.

  • Advanced Chemistry Page Index and LinksETHANOL: Ethanol structure
  • Ethanol is used as a solvent, as a bio–fuel (can be mixed with petrol or used directly), and used to make 'ethyl esters' (see below) as well as the 'potent' chemical present in alcoholic drinks!
    • The % alcohol in wines, spirits and beer varies from 1–40%.
      • The alcohol (ethanol) used in beer and wines is made by fermentation, NOT from ethene derived from cracking crude oil.
      • The fermentation chemistry to produce alcoholic drinks is outlined below.
    • There are health and social issues about the medical and behavioural aspects of alcohol consumption. Alcohol causes liver damage and addiction problems.
    • Binge drinking and alcohol dependency can cause major social problems both within a family and for the wider community.
    • Methylated spirit is mainly ethanol but poisonous and nasty tasting chemicals like methanol are added so it is not used as a beverage!
  • Ethanol can be produced by fermentation of sugars. The raw material sugar (from sugar cane or sugar beet) is mixed with water and yeast at just above room temperature. The yeast contains enzymes which are biological catalysts. The sugars react to form ethanol and carbon dioxide. The carbon dioxide is allowed to escape and air is prevented from entering the reaction vessel to stop oxidation of ethanol to ethanoic acid ('acetic acid' or vinegar!). When the reaction is over the ethanol is separated from the reaction mixture by fractional distillation to make a petrol additive fuel or whisky!
    • e.g. glucose (sugar) == enzyme ==> ethanol + carbon dioxide
      • C6H12O6(aq) ==> 2C2H5OH(aq) + 2CO2(g) 
    • The progress of the fermentation can be followed by measuring the density of the fermented liquid with a hydrometer. Ethanol/alcohol is less dense than water/sugar so the density changes as the sugar is converted into alcohol.
    • fractional distillation diagram and theoryEthanol, in a solution made from fermented sugar cane, can be concentrated by fractional distillation.
      • In Brazil it is blended with petrol to give an alternative motor vehicle fuel (gasohol) i.e. an example of a bio–fuel.
      • C2H5OH(l) + 3O2(g) ==> 2CO2(g) + 3H2O(l) + heat energy from the exothermic reaction
    • The natural fermentation process would have discovered by accident after its products were sampled and so beer has been brewed for thousands of years. Most people in medieval times would have drunk weak beer every day because it was less harmful than polluted water supplies apart from pure natural spring water.
  • Ethanol can also be produced by the reaction of steam and ethene (from oil cracking) in the presence of a strong acid catalyst (Phosphoric acid). The reversible reaction is carried out at a moderately high temperature (e.g. 300oC) and a high pressure (e.g. 60 x atmospheric pressure). The higher temperature and catalyst speed up the reaction and increasing pressure moves the equilibrium to the right (side least gaseous molecules at 300oC)
    • Advanced Chemistry Page Index and Linksethene + water ==> ethanol
    • CH2=CH2 + H2O ==> CH3CH2OH (or C2H5OH)
    • + H2O ==>
    • This is an example of an alkene addition reaction and a hydration reaction because it involves the addition of water to another molecule.
  • Advantages and disadvantages of the two methods of making ethanol
  • Plus a discussion on biofuels and using plant materials for fuels
    • What is a biofuel? What does 'carbon neutral mean'?
      • Biofuels are alternative fuels to fossil fuels produced from plant material.
      • Ideally they are 'carbon neutral', that is the carbon dioxide the they give off on combustion is matched by the plant absorbing the same amount of carbon dioxide. The absorbed carbon dioxide is then utilised in photosynthesis to regenerate the plant material ie remaking the same amount of biofuel again. So, its a sort of mini–carbon cycle.
      • Renewable Biofuels that can be burned to heat water to make steam to drive a turbine and generator. Biofuels are renewable energy sources and come in a variety of forms eg woodchips (trees or waste from timber products), alcohol (ethanol from fermenting sugar cane), biodiesel (from vegetable oil) and biogas (methane from anaerobic digestion of sewage waste) and are all derived from plant materials eg crops or bacterial digestion/decay of waste organic material. The theoretical 'carbon neutral' idea behind using biofuels is that the carbon dioxide released on burning is re–absorbed by plants and utilised in photosynthesis to create the next fuel crop. But, even though this sounds fine in principle, there are still environmental issues eg in Brazil and other countries, huge areas of ecological valuable natural rain forest (habitats, species rich) are being cut down to grow crops for biofuels.
    • Ethanol is an example of a renewable biofuel from plant material.
      • What is 'gasohol'? Ethanol and petrol can be mixed to make a motor vehicle fuel
      • Countries like Brazil, that have no oil reserves of their own, and importing oil is costly, so they are very interested in the manufacture of biofuels, i.e. fuels that can be derived from plant crop materials.
      • Some ethanol is used in blends of petrol ( a 'gasohol') eg in Brazil (called 'alcool') with a cheap labour force (local population or migrant labour) and large land areas growing sugar cane.
        • A typical composition of 'gasohol' might be 10% ethanol (ethyl alcohol) and 90% unleaded petrol (gasoline).
        • It is less polluting than ordinary petrol, it burns more cleanly-efficiently.
        • It also makes the imported oil go a bit further!
      • The renewable sugar cane crop is crushed and the sugar extracted with hot water and the solution fermented with yeast.
        • The alcohol is fractionally distilled from the filtered fermented solution and can then be used as a biofuel.
      • Making renewable fuels like bioethanol from plant materials
        • Benefits of using plant materials to produce fuels
          • Naturally, they are all renewable.
        • Drawbacks and risks to using plant materials to produce fuels
          • Large areas of agricultural land or woodland required.
          • Slow growth eg trees for wood fuels, fast to burn! could demand be matched?,
          • or slow industrial processes like fermentation.
    • Advantages of fermentation
      • In third world countries and more advanced developing countries sugar cane/sugar beet is a common crop and labour is cheap and the process uses a cheap renewable resource eg sugar cane grown in Brazil or sugar beet in England.
      • It does not require any advanced technology compared to a large petrochemical complex based on crude oil.
      • It does not require the importation of expensive crude oil, a non–renewable resource.
      • It is also possible to make a range of organic chemicals from ethanol itself.
    • Disadvantages of fermentation
      • Its a slow reaction and made by an inefficient  batch process, poor quality product e.g. low aqueous concentration of ethanol.
      • The resulting ethanol/alcohol solution is not very concentrated.
        • It only has 4–10%, rest water and waste products e.g. other organic chemicals formed to, and yeast cell residues to remove.
        • Therefore the alcohol must be distilled from the fermentation mixture, so this purification is an extra costly process requiring lots of energy.
      • Large areas of agricultural land are needed and tends towards monoculture agriculture (lack of diversity) – in many countries more food should be grown.
        • Brazil has allowed the cutting down of large areas of valuable rain forest.
        • Therefore, producing ethanol in this way does have quite an environmental impact.
    • Advantages of ethene route
      • Its a fast and efficient continuous process in the petrochemical industry which produces a relatively pure product in bulk quantities.
      • Some countries may have local oil supply (e.g. North Sea for UK, US and Middle East countries).
      • It is much cheaper to produce ethanol from ethene derived from cracking crude oil fractions compared to any plant material and fermentation – oil is still relatively cheap, even if it doesn't seem so when petrol prices go up!
    • Disadvantages of ethene route
      • It uses a non–renewable finite resource of crude oil and more costly technology.
      • Most countries have to import the crude oil to make ethene from cracking – supply may be subject to world market prices or politically unstable situations eg in the Middle East.
    • Biodiesel is another biofuel derived from plant material.
      • Biodiesel can be made from vegetable oil (and animal fat or waste cooking oil) which contain glycerol esters of long–chain fatty acids.
      • These oils/fats like rapeseed oil and soybean oil can re–esterified (transesterification) into methyl esters to make a fuel that can be used directly as diesel fuel or mixed with regular diesel fuel.
        • Vegetable oils are suitable for diesel fuel and release lots of energy on combustion just like petrol or conventional diesel.
        • Biodiesel has similar physical and chemical properties to ordinary diesel from crude oil and burns in conventional diesel engines.
        • The simple word equation for processing vegetable oil into biodiesel fuel is ...
        • oil/fat + methanol ==> biodiesel + glycerol
        • glycerol ester + methanol (an alcohol) ==> methyl ester + glycerol (another sort of alcohol)
      • Pros – advantages of using biodiesel
        • Biodiesel, is in theory, another 'carbon neutral' renewable fuel.
        • Biodiesel is readily biodegradable, so less harmful to the environment if spilled compared to hydrocarbon oils which take much longer to break down.
        • Existing diesel engines don't need converting.
      • Cons – disadvantages of using biodiesel
        • Its relatively expensive to make (small scale production compared to the petrochemical industry based on crude oil).
        • There won't be enough to replace diesel from crude oil.
        • Farmers (especially in third world countries) may switch from essential food production to producing plant oils to make biodiesel, thereby increasing food prices and maybe creating food shortages.
    • 'Alternative fuels'
      • Think in terms of use of renewable resources, storage and use of the fuels, their products of combustion.
      • Ethanol is one of the more recent 'alternative fuels' to traditional fossil fuels like coal, gas and oil.
      • If an efficient source of hydrogen production could be found, this could be another fuel.

      Comparison of two alternatives to vehicle fossil fuels – their 'pros' and 'cons'

      FUEL (both renewable in theory) Advantages of the fuel 'pros' Disadvantages of the fuel 'cons'
      Ethanol a) Can be cheaply produced from sugar cane/beet

      b) Easily stored and distributed as a liquid fuel.

      c) carbon neutral

      d) only products are carbon dioxide and water with no pollutants like sulfur dioxide

      a) Slow rate of mass production

      b) Requires large areas of agricultural land or woodland AND farmers may switch from growing food crops – increasing food prices and possible causing food shortages in third world countries.

      c) Does produce the greenhouse gas carbon dioxide (and water), theoretically reabsorbed by plants, but fast to burn and plants slow to grow.

      d) Ethanol fuels are not widely available.

      e) Car engines need modifying to work with ethanol fuels.

      f) Ethanol costs five times more to produce than 'straight–run' gasoline (and hydrogen is even more expensive).

      Hydrogen a) Endless supply of water

      b) Water is the only product of burning hydrogen, so its very clean non–polluting combustion.

      See also use of hydrogen in fuels cells

      a) Efficient large scale technology not yet developed to produce hydrogen on a large scale eg from electrolysis using solar power electricity – photovoltaic power system, wind turbines or hydroelectric power.

      b) Although water is cheap and plentiful, it requires expensive electrical energy to electrolyse water to split it into hydrogen and oxygen.

      c) As a gas it is more difficult to store, needs a larger storage space (volume) and distribute safely due to it being highly flammable, easily ignited, so risk of explosion if leaked.

      d) You need a special expensive? hydrogen burning car engine that is not widely available.

      e) Hydrogen is an explosive gas and difficult to store and transport safely from the point of view of distribution to consumers.

      f) Most hydrogen used in industry is actually made from fossil fuel hydrocarbons!  (see making hydrogen for the Haber Synthesis of ammonia).

  • Extra general notes on alcohols and the reactions of alcohols including ethanol
  • The alcohols form a homologous series with the same functional group C–O–H. It is the presence of this functional group that gives alcohols their characteristic properties.
    • The simplest homologous series of alcohols have the general formula CnH2n+1OH e.g.
    • You must always make sure the OH group is clear in any molecular structure you draw of an alcohol.
    • The last alcohol structure given below is the full displayed formula which you should definitely know, but you also need to know the various abbreviated ways of writing the molecular structure of alcohols.
    • The simplest alcohol with the lowest carbon number of one is methanol (the 1st in the homologous series of alcohols is shown below, followed by the next four in the series.
    • or or
    • Ethanol, discussed in detail above, is the 2nd in the series,
  • Advanced Chemistry Page Index and LinksThe next three are propanol (strictly speaking propan–1–ol, 3rd in series), butanol (strictly speaking butan–1–ol, 4th in series) and pentanol (strictly speaking pentan–1–ol, 5th in series), note all the alcohol names end in ...ol, which means the molecule is an alcohol. The –1–ol means the OH group is on the first carbon atom of the molecule's chain –C–C– etc.
  • Physical and chemical properties of alcohols and their uses
    • All the alcohols are colourless liquids with a characteristic 'pleasant'? odour.
      • The first three alcohols dissolve in water (miscible) but as the carbon chain grows longer,, they become less and less soluble in water.
    • The boiling point steadily rises from one alcohol to next with increase in molecule size (increase in carbon number).
    • They all behave chemically in the same way (same functional group C–OH) e.g. they all reaction with sodium, they all react with carboxylic acids to form esters.
    • All alcohols are flammable and readily burn when ignited in air.
    • Alcohols are used as solvents – they dissolve a wide range of compounds, some that water dissolves, but others like oils, fats and hydrocarbons dissolve in alcohols, which are insoluble in water.
      • Ethanol is used as a solvent in cosmetic products like perfumes and aftershave lotions.
      • In these products the aromatic oils and water base become compatible in the alcohol.
    • 'Methylated Spirits' ('meths') is mostly ethanol with other chemicals added to it to make it unpalatable to drink, since pure ethanol is highly poisonous.
      • A purple dye is added so you don't drink it by mistake!
      • Methylated sprits is used as a fuel in camping cooker burners (spirit burners - combustion use) and for cleaning paint brushes (solvent use).
      • Its use as fuel for cars was discussed further up the page.
    • Details of the reactions of alcohols are given below.
  • A short note on ESTERS: Esters are another homologous series of organic compounds
    • e.g. Ethyl ethanoate, an ester,  is formed by the reaction of carboxylic acid and an alcohol e.g.
    • ethanoic acid + ethanol ethyl ethanoate + water
    • + + H2O
      • sometimes more simply written as
      • CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O
    • General word equation: carboxylic acid + alcohol ==> ester + water
    • Esters are used in perfumes and food flavourings. Lots of details in section 10. for the ..
    • Procedure for preparing an ester, uses of esters, details of esters & carboxylic acids
  • Alcohols react with sodium to form hydrogen and an alkoxide
    • alcohol + sodium ==> an alkoxide + hydrogen gas
    • Normal 'hydrogen' gas fizzing is observed and the salt product is soluble in the alcohol itself e.g.
    • ethanol + sodium ==> sodium ethoxide + hydrogen
    • 2C2H5OH + 2Na ==> 2C2H5ONa+ + H2 
    • similarly ...
      • methanol + sodium ==> sodium methoxide + hydrogen
        • 2CH3OH + 2Na ==> 2CH3ONa+ + H2
      • and ...
      • propanol + sodium ==> sodium propoxide + hydrogen
        • 2CH3CH2CH2OH + 2Na ==> 2CH3CH2CH2ONa+ + H2
  • Ethanol can be oxidised to form ethanoic acid
    • Which is a useful organic chemical. BUT it is this oxidation of ethanol that results in alcoholic drinks turning sour (e.g. cider, wine) when exposed to air!
    • The fruit material already contains the enzymes that catalyse the oxidation of ethanol ('alcohol') in the presence of air.
    • ethanol + oxygen ==> ethanoic acid + water
    • CH3CH2OH + O2 ==> CH3COOH + H2
    • + O2 ==>  + H2O
    • This oxidation can also be done in the laboratory by heating the ethanol with a mixture of sulphuric acid and potassium dichromate(VI) solution.
      • This is a complex reaction and the mixture turns from orange to green as the ethanol is oxidised.
      • In industry you can oxidise ethanol directly with oxygen on a large scale.
  • When burned, ethanol, like any alcohol, on complete combustion forms carbon dioxide and water
    • ethanol + oxygen ==> carbon dioxide + water
      • CH3CH2OH(l) + 3O2(g) ==> 2CO2(g) + 3H2O(l)
    • Similarly, but the symbol equations are more awkward to balance  ...
      • methanol + oxygen ==> carbon dioxide + water
        • 2CH3OH(l) + 3O2(g) ==> 2CO2(g) + 4H2O(l)
      • and ...
      • propanol + oxygen ==> carbon dioxide + water
        • 2CH3CH2CH2OH(l) + 9O2(g) ==> 6CO2(g) + 8H2O(l)
          • a bit much to balance at GCSE level!, don't worry about it!
  • Ethanoic acid (old name 'acetic acid') is the basis of vinegar and is also used in making esters (e.g. for flavourings like pear drop essence as mentioned above).
  • Ethanol can be dehydrated to ethene by passing the alcohol vapour over heated aluminium oxide catalyst.
    • ethanol ===> ethene + water
    • CH3CH2OH ===> CH2=CH2 + H2
    • ==> + H2O
    • This reaction is potentially an important source of organic chemicals e.g. plastics from a renewable resource since the ethanol can be made by fermentation of carbohydrates etc.
  • Alcohols from propanol upwards, i.e. from carbon number 3 or greater, will form isomers.
    • Isomers are molecules with the same molecular formula but the atoms can be arranged in two or more different ways e.g. there are two propanols with the molecular formula C3H8O
      • and alcohols and ether structure and naming (c) doc b
      • they are similar physically and chemically, but they are not identical.
    • You will find plenty of examples on the Advanced organic chemistry page for alcohols
Chemically, cholesterol, which contains the alcohol group –OH is a sterol, a sub–group of organic molecules called steroids (BUT not the body building type of steroid!, more to do with the metabolism of fats!). Cholesterol is an essential steroid–sterol to humans but if too much is produced it can cause heart disease. The image on the right gives the skeletal formula structure of cholesterol (this structure representation is usually only dealt with at advanced level). All the lines in the structure represent bonds between carbon atoms except the 'wedge dash' to the –OH alcohol group in the bottom left of the molecule. Also note the 'alkene' double bond functional group to the right of the –OH group. So, even at advanced level, the same organic functional groups crop up!

Advanced Chemistry Page Index and Links[Cholesterol image from NIST]

 

Multiple Choice Quizzes and Worksheets

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (easier–foundation–level)

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (harder–higher–level)

KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry

and (c) doc b 3 linked easy Oil Products gap–fill quiz worksheets

ALSO gap–fill ('word–fill') exercises originally written for ...

... AQA GCSE Science (c) doc b Useful products from crude oil AND (c) doc b Oil, Hydrocarbons & Cracking etc.

... OCR 21st C GCSE Science (c) doc b Worksheet gap–fill C1.1c Air pollutants etc ...

... Edexcel 360 GCSE Science Crude Oil and its Fractional distillation etc ...

... each set are interlinked, so clicking on one of the above leads to a sequence of several quizzes

Advanced Level Organic Chemistry revision notes


keywords equations: C6H12O6 ==> 2C2H5OH + 2CO2 * C2H5OH + 3O2 ==> 2CO2 + 3H2O * CH2=CH2 + H2O ==> CH3CH2OH (or C2H5OH)


Notes information to help revise KS4 Science Additional Science Triple Award Separate Sciences Chemistry revision notes for GCSE/IGCSE/O level Chemistry Revision–Information Study Notes for revising AQA GCSE Science AQA GCSE Chemistry, Edexcel GCSE Science, Edexcel GCSE Chemistry, OCR 21st Century Science Chemistry, OCR Gateway Science chemistry, WJEC/CBAC GCSE science–chemistry CCEA/CEA GCSE science–chemistry (and courses equal to US grades 8, 9, 10)


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