School chemistry revision 14-16 GCSE level chemistry notes: Fermentation, structure & chemistry of alcohols - ethanol

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9A. ALCOHOLS - including the production, physical and chemical properties and uses of ethanol

Primarily for IGCSE/GCSE chemistry revision notes, but quit suitable as an introduction for A Level/IB/US grades 10-12 chemistry students too

This page covers basic physical and chemical properties of alcohols like ethanol, including equations, experiments, displayed formula of ethanol and methanol, ball and stick model of ethanol, comparison of methods of ethanol manufacture

See also 9b. Biofuels, alternative fuels

All my 14-16 GCSE level chemistry revision notes

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All my advanced A level organic chemistry notes

INDEX of Advanced A Level revision notes on the chemistry of ALCOHOLS

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Sub-index for this page

(1) Ethanol and the homologous series of alcohols

(2) The structure, physical properties and brief mention of uses of ethanol

(3) The production of ethanol by fermentation and class experiments and demonstrations

(4) The social and medical issues associated with drinking alcoholic beverages

(5) Industrial manufacture of ethanol from ethene and compared to fermentation

(6) More notes on the homologous alcohols and reactions of alcohols including ethanol

(7) Some physical properties of alcohols related to their use as solvents

(8) Chemical properties of alcohols – important reactions and more on uses

See also

More on the use of ethanol as a biofuels

Making ethyl esters (separate page)

 Doc Brown's chemistry revision notes: GCSE chemistry, IGCSE  chemistry, O level & ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old students of chemistry

(1) 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, the homologous series we call alcohols, which all have the C–OH 'hydroxy' functional group in their structure.

The full displayed formula for the first five members of the homologous series of ALCOHOLS

The diagrams show ALL the covalent bonds (C-H, C-C, C-O and O-H) in alcohol molecules, C-OH being the alcohol functional group

The structural formulae can also be written as:


The general formula for this particular alcohol series is CnH2n+1OH   (n = number of carbon atoms in molecule)

(Note: the technical names for the 3rd, 4th and 5th displayed above are propan-1-ol, butan-1-ol and pentan-1-ol)

Methanol, ethanol, propanol and butanol are all colourless flammable liquids that dissolve in water to give neutral solutions (pH 7)

Don't write alcohol formula as molecular formula, always give the displayed or structural formula clearly showing the alcohol functional group, which is -OH

e.g. or CH3OH, NOT CH4O  and   or CH3CH2OH or C2H5OH, NOT C2H6O

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(2) The structure, physical properties and uses of ethanol

  • Ethanol and other alcohols - molecular structure, the physical and chemical properties of ethanol
  • or or or
  • The first formula is the simplest formula to show the structure of ethanol and the last image is the full graphic structural displayed formula of ethanol (full structural formula), i.e. it shows all the atoms and the bonds linking them together in the molecule.

2D displayed formulae alcohols and ether structure and naming (c) doc b and 3D impression of the displayed formula alcohols and ether structure and naming (c) doc b of methanol

3D ball and stick model of methanol CH3OH AND 3D space-filling model of methanol CH3OH

3D ball and stick model of methanol CH3OH AND 3D space-filling model of methanol CH3OH

full Lewis dot and cross diagram for methanol molecule showing inner shell electrons of carbon and oxygen Dot and cross diagram for the methanol molecule showing the inner shell electrons of carbon and oxygen. Carbon's electrons are 2.4 (4 outer valency electrons, 4 short of noble gas), oxygen 2.6 (6 outer valency electrons, 2 short of noble gas) and hydrogen just 1.

ball and stick model of ethanol molecular structure The ball and stick model of the ethanol molecule read as CH3-CH2-OH.

displayed formula of ethanol - the full structural formula molecular structure 2D displayed formula of ethanol, full structural formula, alcohols and ether structure and naming (c) doc b 3D version of the displayed formula of ethanol

dot and cross diagram of ethanol molecule molecular structure The dot and cross diagram of the ethanol molecule.  Only the outer electrons are shown in the dot and cross diagram above.  The 2 inner electrons of carbon and oxygen are not shown.  Again, carbon's electrons are 2.4 (4 outer valency electrons), oxygen 2.6 (6 outer valency electrons) and hydrogen just 1. This is perhaps going beyond GCSE level?

  • Ethanol is used as a solvent, as a biofuel (can be mixed with petrol or used directly), and used to make 'ethyl esters' (see Esters page) 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.
      • Note that ethanol can be made from waste biomass (see Biofuels)

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(3) Ethanol can be produced by fermentation of sugars

and a class experiment to illustrate the manufacture of ethanol ('alcohol') from sugar

  • The raw material is usually a sugar from a carbohydrate source e.g. sugar cane or sugar beet, molasses - a by-product from processing sugar cane and sugar beet into sugar, starch from maize, potatoes or wheat.
  • The sugar is mixed with water and yeast at just above room temperature (30-40oC) in a reactor vessel (a big vat!) from which air (oxygen) is restricted.
    • The fermentation is carried out in steel containers which are easier to sterilise than traditional wooden barrels or vats.
    • The fermenters must be sterilised to stop other micro-organisms growing e.g. Acetobacter produces ethanoic acid ('acetic acid') from sugars - great for vinegar production, but who wants to drink sour beer or wine!
  • The yeast contains an enzyme called zymase which acts as the biological catalyst to convert sugar to ethanol in fermentation.
  • The enzyme works best at an optimum of pH ~6.
  • Under anaerobic conditions at an optimum temperature of 30oC to 40oC, the sugars react via the enzymes in the yeast cells to form ethanol and carbon dioxide gas.
  • If the temperature is too low, the reaction is too slow. If the temperature is to high the enzyme is denatured - the molecular structure is distorted so the active site doesn't work properly.
  • Oxygen from air must be excluded to maintain anaerobic conditions - the reaction is an example of anaerobic respiration.
    • Other enzymes present can catalyse the oxidation of ethanol to ethanoic acid (acetic acid, vinegar), not a nice taste.
  • The fermentation reaction of the sugar obtained from the sugar cane or sugar cane is ...
  • glucose (sugar) == enzyme ==> ethanol + carbon dioxide
  • The carbon dioxide is allowed to escape and air is prevented from entering the reaction vessel to stop oxygen oxidising ethanol to ethanoic acid ('acetic acid' or vinegar!) ensuring the reaction occurs under anaerobic conditions. The acid would also lower the pH lowering the effectiveness of the enzyme and it wouldn't do the taste of beer any good either.
  • The fermentation reactions stop when the concentration of alcohol reaches a maximum of 10-20% when the alcohol kills the yeast cells.
  • When the reaction is over, the mixture is filtered, or the 'dead yeast sludge' allowed to settle out and the mixture decanted (poured off leaving the sludge behind) prior to distillation.
  • The fractional distillation (more details below) concentrates the alcohol for particular products.
    • e.g. wine is distilled to make brandy, whisky is made from fermented grain like barley, vodka is very concentrated ethanol and is also made from fermented grain or potatoes.
    • Some spirits have up to 40% alcohol in them, beers have about 3-4% alcohol in them - but distillation isn't necessary.
    • The boiling point of ethanol, 78oC, is lower than water, 100oC, so theoretically, the ethanol should distil off first. However, there is a maximum of ~96% ethanol in the distillate.
      • An azeotropic mixture is formed of 95.6% ethanol and 4.4% water, which cannot be separated by fractional distillation, but it is sufficiently concentrated to be used as the fuel bioethanol e.g. 5-20% of petrol (see section 9B on alternatives to fossil fuels).
  • Teacher note - class fermentation experiment
    • A simple recipe for small groups of pupils:
    • Dissolves ~10g of granulated sugar in 100 cm3 of water to make a ~10% solution.
    • Pour into a 250 cm3 conical flask.
    • Add a teaspoon of dried yeast.
    • Seal the conical flask with a rubber bung and an inverted U tube Π.
      • You can just use a cotton wool plug, but more awkward to get a gas sample to test.
    • Keep in a warm place (if possible) between lessons.
    • In fact after a few hours (maybe by the end of the lesson?) the student can test for carbon dioxide with limewater - the carbon dioxide should give a white precipitate with the limewater.
    • I used to ask the students to bring some fruit juice in their school bag and add it to the solution, or make up the fruit juice to 100 ml and add the sugar and yeast.
      • Not sure on H & S regulations on this point these days?
    • In the next lesson I would then gather all the fermented mixtures and filter them all into a large distillation flask.
    • I'd then perform 'with great ceremony' the fractional distillation described below.
    • Then you demonstrate the flammability of the 'firewater' by burning the odd drop to show it was fuel.
    • They were also allowed to smell the product, which had a lovely fruity odour.
  • fractional distillation diagram and theoryMore details on how is the ethanol separated from a fermented mixture
    • The ethanol is separated from the reaction mixture by fractional distillation to make a petrol additive fuel or whisky! Ethanol has a lower boiling point (78oC) than water (100oC) and distils off first giving a concentration of up to 95% ethanol. The two vapours separate out in the fractionating column, the lower boiling ethanol rising to the top, passing out into the condenser, condensing to a liquid for collection in some suitable container.
    • Most of the higher boiling water condenses back into a liquid in the fractionating column and runs back into the flask. This distillation is needed to make spirits like brandy and whisky. The laboratory process is illustrated in the diagram on the right using a glass column filled with glass beads and connected to the distillation flask and a Liebig condenser (see separation of mixtures - distillation for more explanation).
  • Extra notes on the fermentation process ....
    • 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.
    • When the concentration of alcohol reaches about 10–20% the fermentation reaction stops because the yeast cells are then killed by this high concentration of ethanol.
    • Pure ethanol is classed as a toxic poison just like cyanide and arsenic!
    • Its important to have the optimum temperature (30oC – 40oC) otherwise the efficiency of the process is affected. If the temperature is to high the enzymes in the yeast cells are denatured and if the temperature is too low, the reaction is too slow (see graph of rate of reaction below).
    • The diagram (c) doc b graphically illustrates the idea of the optimum temperature by showing the rate of reaction varies for a fermentation process.
    • The diagram (c) doc b graphically illustrates the idea of the enzyme zymase working best at around a pH of 4-8, average pH 6-7. In very acid or moderate to strong alkaline conditions the zymase enzyme becomes very ineffective and the rate of reaction for fermentation becomes extremely slow, inefficient and uneconomic (same argument for temperature too).
    • For more details about enzymes see Enzymes and Biotechnology
    • Ethanol, in a solution made from fermented sugar cane or sugar beet, can be concentrated by fractional distillation.
      • The fermentation process is used to make wines and beers for the food and drinks industry. Brandy is made from distilling wine to concentrate the alcohol. Whisky is distilled from fermented grain (e.g. barley) and vodka is distilled from fermented grain or potatoes. Beers typically have 3–4% ethanol, most wines in the supermarket seem to be ~15% and spirits may have a concentration of up to 40%.
      • In Brazil ethanol is blended with petrol to give an alternative motor vehicle fuel (gasohol) i.e. an example of a biofuel. See also 9b. Biofuels
      • C2H5OH(l) + 3O2(g) ====> 2CO2(g) + 3H2O(l) 
      • Heat energy released from the exothermic reaction
      • You produce various blends of petrol by mixing ethanol from fermentation with petrol from the fractions of distilled crude oil.
    • 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.

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(4) The social and medical issues associated with drinking alcoholic beverages

  • Ethanol ('alcohol') is the major ingredient in the drinks industry producing beers, wines and spirits from fermentation processes.
  • Ethanol has a powerful physiological effect on the body, particularly the brain.
  • Alcohol containing drinks initially make you feel relaxed and less inhibited.
  • However, there are health and social issues about the medical and behavioural aspects of alcohol consumption e.g.
  • Ethanol reduces brain activity e.g. slower thinking and slower reaction responses to a changing situation hence the obvious dangers from drink driving! Many serious injuries and deaths result from 'drink driving' accidents.
  • Your judgement is impaired and your general physical coordination, including balance, are much affected.
  • Imbibing large quantities of alcohol can produce unconsciousness and a potentially fatal coma.
  • Alcohol causes dehydration and brain cell damage leading to decrease in brain function and long–term memory loss.
  • Alcohol causes liver damage and a very serious condition, a liver disease called cirrhosis of the liver, you may even need a liver transplant if lucky enough to obtain one if your liver eventually fails to function.
  • and addiction problems adding unnecessary extra costs for the NHS (in the UK).
  • Binge drinking and alcohol dependency, especially among young people, can cause major social problems both within a family and for the wider community with anti–social behaviour. This again cost society in policing and doctors in A & E.
    • Drinking too much can lead to violent behaviour, silly and sometimes dangerous  'loutish' acts.
    • Alcoholism can lead to family breakdown, loss of job and eventually homelessness.
    • Irresponsible sexual behaviour ranging from not using contraception, increasing chance of pregnancy or passing on sexually transmitted diseases to the worst case scenario, rape.
  • Liver disease from alcohol abuse is now showing up in young men and women in their 20s, but there are plenty of older people drinking to much too.
    • Just out of interest, doc b is actually allergic to alcohol and can become quite ill after one drink! maybe its a blessing? maybe not!, but I'm very relaxed and relatively unstressed in my retirement and thoroughly enjoying to continue to write this website without the need of either relaxants or stimulants!
  • Methylated spirit is mainly ethanol but poisonous and nasty tasting chemicals like methanol are added so it is not used as a beverage!
    • Deaths have occurred from drinking 'meths' and from contaminated illicit alcoholic drinks.

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(5) Industrial manufacture of ethanol from ethene and compared to fermentation

  • Ethanol can also be produced by the reaction of steam and ethene (an alkene from oil cracking) in the presence of a strong acid catalyst (phosphoric acid, H3PO4). Beyond the alcoholic drinks industry, this is the main industrial method of manufacturing ethanol.
    • The reversible reaction is carried out at a moderately high temperature (e.g. 300oC) and a high pressure (e.g. 60–70 times atmospheric pressure).
    • The higher temperature and phosphoric acid catalyst speed up the reaction and increasing pressure moves the equilibrium to the right (side least gaseous molecules at 300oC)
    • ethene + water ====> ethanol
    • CH2=CH2 + H2O ====> CH3CH2OH (or C2H5OH)
    • doc b oil notes ====>
    • This is an example of an alkene addition reaction and a hydration reaction because it involves the addition of water to another molecule.
    • Since there is only one product, the atom economy is 100%.
    • This process can be carried out fast, efficiently and continuously on a large industrial scale to produce high quality ethanol compared to the slow fermentation process producing impure ethanol (see discussion below).
      • This is done on an industrial scale, and the products from the reaction chamber are passed into a condenser where the higher boiling ethanol and unreacted water readily condense out.
      • When the gases are first passed over the catalyst, the yield is only 5%.
      • The more costly unreacted ethene can be recycled because it remains as a gas (much lower boiling point than water or ethanol) and so non is wasted.
      • The separated ethanol/water mixture is concentrated and purified by fractional distillation.
      • This means there is no waste and the atom economy is 100%.
    • The ethene is obtained from catalytic or steam cracking reactions at high temperatures of 450oC to 900oC of alkane hydrocarbons from the fractional distillation of crude oil e.g.
      • butane ==> ethane + ethene
      • doc b oil notes doc b oil notes doc b oil notes doc b oil notes doc b oil notes
      • the ethane can be further cracked to make more ethene
      • ethane ==> ethene + hydrogen
      • doc b oil notes doc b oil notes doc b oil notes
      • so you can have, for example, a synthetic route for ethanol as follows ...
      • crude oil ====> ethane ====> ethene ====> ethanol
      • Note that ethanol made from ethene is NOT a renewable method of alcohol production because ethene is made from cracking hydrocarbons from crude oil.
      • Ethanol from plant material like sugar cane or sugar beet can be considered renewable.
  • Advantages and disadvantages of the two methods of making ethanol
  • We are talking fermentation and hydration of ethene and the 'pros' and 'cons' of the ways of making ethanol ('alcohol').
    • See also 9b. Biofuels
    • BUT first for instance, are the two methods of ethanol production 'green' and 'sustainable' processes?
      • Fermentation: glucose sugar ==> ethanol + carbon dioxide
        • C6H12O6  ===>  2C2H5OH + 2CO2
          • atom economy is 51% (see calculations), low due to waste carbon dioxide.
      • AND, the ethene route involves two chemical reactions ...
      • (i) Cracking: ethane (and other larger hydrocarbons) ===> ethene + hydrogen

        • C2H6 ===> C2H4 + H2
          • molecular masses 30, 28 and 2 respectively.
          • atom economy = 100 x mass of useful product / mass reactants
          • atom economy for cracking = 100 x 28 / 30 = 93%, very high, little waste
      • (ii) Hydration of ethene: ethene + water  ==>  ethanol
        • H2C=CH2  +  H2O  ===> CH3CH2OH
          • atom economy is 100%, simple addition reaction with one product.
    • Factors to consider include listed below ... which you can merge in with the 'pros' and 'cons' discussion that follows
      • What is the source of raw material? Will it run out?
        • Fermentation: Sugar beet and sugar cane grow quickly, particularly in warm climates and labour may be very cheap in third world countries. So we have a sustainable renewable resource thanks to photosynthesis.
        • Cracking & ethene hydration: Crude oil, from which ethene is obtained by cracking, will eventually run out, and oil is a non-renewable resource, so not sustainable in the distant future.
      • What are the energy costs? and catalyst costs?
        • Fermentation: Some energy is required to keep the fermenting mixture at the optimum temperature of 30-40oC. Yeast is relatively cheap to produce, since it reproduces and grows quite naturally.
        • Cracking & ethene hydration: Both processes need energy to sustain high pressure and high temperature reaction conditions. There is also an extra cost for catalysts which would cost a lot more than yeast.
      • Are there any implications for climate change? Are there any environmental issues?
        • Fermentation: Carbon dioxide is produced in the process, contributing to global warming, but, isn't it recycled via photosynthesis when more sugar beet or sugar cane is grown?
        • Cracking & ethene hydration: Neither processes directly harms the environment, though there are dangers from oil spillages in transporting oil in tankers.
      • What is the atom economy? Is there much waste.
        • Fermentation: The atom economy is only 51% (see calculation) because 49% by mass of the sugar is lost as carbon dioxide. Not only that, as the yeast cells are killed off by the high concentration of ethanol, not all of the sugar is actually fermented further decreasing the efficiency of the process.
        • Cracking & ethene hydration: Cracking ethane and other hydrocarbons is quite high (93%) with only hydrogen gas as the waste product (but this can be used in hydrogenation processes and making ammonia). The atom economy is very high for the hydration of ethene (theoretically 100% with just one product).
      • Is it a profitable process?, does it make a profitable product?
        • Fermentation: It would seem so from the point of view of the food and drinks industry, breweries and vineyards make good profits, though a vineyard's economy-profits can be dependent on the weather. BUT, is it profitable to use the alcohol as a biofuel? e.g. blended with petrol from oil.
        • Cracking & ethene hydration: Both processes are fast and efficient and can be run on a continuous basis and at the moment the raw materials, from oil, are relatively cheap, but the price will increase as oil reserves become depleted in the future.
      • Does the fermentation process have any issues with society? e.g. are there particular benefits or risks?
        • Fermentation: There are no particular health and safety issues or great risks for the surrounding local communities, unlike the potential hazards of running an oil refinery. The risks come later with alcohol abuse! Benefits may include jobs for the local economy and revenue for local farmers growing the sugar cane or sugar beet.
        • Cracking & ethene hydration: There are important health and safety issues to deal with in the petrochemical industry. You are dealing with highly flammable and explosive gases being processed at high temperatures and pressures. This poses dangers at all the time and so all the processes must be carefully monitored and controlled, this is also increases the costs of the processes because it requires very standards of engineering and safety measures.
      • Are there any issue with waste products?
        • Fermentation: The waste carbon dioxide can be safely released into the atmosphere, but it could be used in fizzy carbonated drinks or even pumped into greenhouses to increase the rate of photosynthesis - case of good recycling?
        • Cracking & ethene hydration: The only waste product from cracking is hydrogen gas, but this can be used to hydrogenate vegetable oils to make margarine or reacted with nitrogen to make ammonia.
    • Summing up the advantages of fermentation to make ethanol
      • 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 costly advanced technology compared to a large petrochemical complex based on crude oil.
      • There is no need for high pressure chemical reactors and less energy needed at the lower reaction temperature required.
      • It does not require the importation of expensive crude oil, a non–renewable resource and since based on an agricultural system, it aught to be sustainable with a long–term future.
      • It is also possible to make a range of organic chemicals from ethanol itself.
    • Summing up the disadvantages of fermentation to make ethanol
      • Its a slow reaction and made by an inefficient  batch process, poor quality product e.g. low aqueous concentration of ethanol. A batch process means you have to keep on emptying the reaction vessel (e.g. fermentation vat or tank) and clean it out and refill with reactants i.e. yeast and sugar solution.
      • The yield of the reaction is less than that from the hydration process.
      • The product is not very pure and expensive purification via fractional distillation is required, and even that has a limit of 95% purity.
      • 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.
        • The atom economy is lower than that from the hydration of ethene.
          • atom economy = 100 x mass of useful products / mass of reactants
          • from the equation: C6H12O6 ====> 2C2H5OH + 2CO2
          • and molecular masses: Mr(glucose)= 180 and Mr(ethanol) = 46, (C = 12, H = 1, O = 16)
          • atom economy = 100 x (2 x 46) / 180 = 51% for fermentation
          • It is theoretically 100% for the ethene hydration route.
      • 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 the hydration of ethene route to ethanol manufacture
      • Its a fast and efficient continuous process in the petrochemical industry which produces a relatively pure product in bulk quantities. Its NOT a batch process, the ethene and water can be rapidly fed into the reactor chamber and the product collected, such a system may run for months without any need to replenish the catalyst or carry out maintenance work.
      • 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!
      • The product formed is much purer than that from fermentation and requires less processing to obtain 100% pure ethanol, known as 'absolute alcohol'.
      • On the initial pass of the ethene–water mixture over the catalyst only a small percentage is converted to ethanol, BUT, it is possible to recycle the unreacted ethene and so the eventual yield is up to 95%, much higher than the yield from fermentation.
      • The reaction has a higher atom economy, in fact it is theoretically 100% since the reaction involves the simple addition of two molecules.
    • Disadvantages of hydration of ethene route to ethanol manufacture
      • It uses a non–renewable finite resource of crude oil and more costly technology and may not be sustainable in the distant future.
      • 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.
      • In the long term, as oil reserves decrease, the production of ethene from cracking oil hydrocarbons may become increasingly costly.
    • Is bioethanol a carbon neutral fuel?

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(6) More notes on the homologous alcohols and reactions of alcohols including ethanol

  • A homologous series is a family of compounds which have the same general formula and have a similar molecular structure and similar chemical properties because they have the same functional group of atoms e.g. C–OH for an alcohol.
    • Members of the alcohol homologous series have similar physical properties such as appearance, melting/boiling points, solubility etc. BUT show trends in them e.g. steady increase in melting/boiling point with increase in carbon number or molecular mass or in the case of alcohols, they become progressively less soluble in water.
    • It is important to realise that members of a given homologous series like alcohols have similar chemical reactions because their molecules contain the same functional group (OH) and so you can predict the chemical reactions and products of the other members of the alcohol series
    • The hydroxy functional group, C–O–H, is the group atoms common to all members of the alcohol homologous series that confer a particular set of characteristic chemical reactions on each alcohol molecule of the series.

    • The simplest homologous series of alcohols have the general formula CnH2n+1OH where n = 1, 2, 3 etc. i.e. the number of carbon atoms in the alcohol molecule (see the diagram of the first five alcoholism the diagram near the top of the page).
    • You must always make sure the C–O–H group (OH, hydroxy) is clear in any molecular structure e.g. displayed formula, you draw of an alcohol i.e. the C–O–H bonds are clearly shown.
      • C2H5OH may not be good enough, but ticks all the boxes!
    • 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,
  • The next three alcohols 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.

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(7) Some physical properties of alcohols related to their use as solvents

  • 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 fourth alcohol, butanol, is quite soluble in water.
  • The boiling point steadily rises from one alcohol to next with increase in molecule size (increase in carbon number), just like the boiling points rise in alkanes.
  • Comparison of alcohols with alkanes and water
Property alcohols

e.g. CH3CH2OH


alkanes – hydrocarbons

e.g C6H14


non-organic solvent



Physical appearance at room temperature and volatility Alcohols are colourless liquids, large alcohol molecules may be white waxy solids. Ethanol is quite volatile and readily evaporates into the air. Colourless gases or liquids, the first few alkanes methane to butane are gases, the rest are colourless liquids or white waxy solids. Water is a colourless liquid, but not as volatile as ethanol.
Boiling point – for the same size of molecule (molecular mass) alcohols have a much higher boiling point than alkanes Alcohols have a wide range from 65oC to over 500oC

ethanol boils at 78oC

Alkanes have a wide range from –164oC to over 500oC

Hexane boils at 69oC

100oC, this is very high for a very small molecule, but since ethanol only boils at 78oC, the two can be readily separated by fractional distillation.


Solubility in water The first few alcohols like ethanol are completely soluble (miscible), after that they become progressively less soluble in water All hydrocarbons like alkanes are insoluble in water
What will they dissolve? The first few alcohols are very useful industrial solvents e.g. methanol and ethanol dissolves a wide variety of compounds including hydrocarbons to some extent, other alcohols, carboxylic acids. Ethanol is used to dissolve molecules used in the perfume and cosmetic industries. The important point here is that ethanol will dissolve many compounds water can't. Methanol cannot be used in cosmetic products - its too toxic! Alkane liquids like hexane have limited use as solvents, they will dissolve other hydrocarbons from diesel to waxes, but not much else. Water is very useful solvent, dissolves a wide variety of compounds e.g. lots of salts, some organic compounds like sugars, smaller alcohols, smaller carboxylic acids (like ethanoic acid). Water is used widely in all sorts of domestic products from cosmetics to cleaning fluids as the main media or solvent.
  • As mentioned above, alcohols very useful 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 because it mixes well with natural oils (smell 'scent') and water which makes up the bulk of many cosmetic preparations.
    • In these sorts of cosmetic products the aromatic oils and water base become compatible in the alcohol.
    • Esters are also used as solvents
    • Why does a substance dissolve in one liquid solvent but not another?
      • There are three particle interactions going on if you mix one substance with another e.g. a liquid solvent that may or may not dissolve a solid.
      • The three possible attractions are (i) solid ... solid, (ii) solid ... liquid and (iii) liquid ... liquid.
      • The relative strength of these attractive intermolecular forces decides whether e.g. a solid will dissolve in a particular solvent.
      • For example, nail varnish will not dissolve in water, but will dissolve in organic solvents like an ester, alcohol or acetone.
      • Nail varnish is insoluble in water because the intermolecular forces between the nail varnish molecules themselves, and between the water molecules themselves are much stronger than the attraction between water and the nail varnish molecules, so the nail varnish cannot possibly dissolve in water. Forces (i) and (iii) override force (ii)
      • However, nail varnish will dissolve in organic solvents like butyl ethanoate or ethyl ethanoate (esters, old names butyl acetate and ethyl acetate), ethanol ('alcohol') and propanone (old name acetone) solvents. Here the organic solvent intermolecular attraction to the nail varnish molecules can override the nail varnish ... nail varnish and the solvent ... solvent intermolecular forces and the nail varnish will dissolve. In this case attractive force (ii) overrides both attractive forces (i) and (iii).
      • Since different solvents are different molecular affinities for different substances, the solubility of a solute in a solvent can vary quite considerably from one solvent to another.
      • The question of which solvent you choose to use to dissolve a substance depends on two main factors ..
        • (a) How soluble is the substance in the solvent?
        • (b) How safe is to use the solvent? e.g. in terms of inhaling vapour or spillage on the skin (gloves!), is it harmful?, irritating?, even toxic?, and is it highly flammable, so more dangerous to use.
        • Chlorinated organic solvents e.g. trichloromethane ('chloroform') tend to be harmful, alcohols and esters are safer but are more flammable.
        • This section is repeated in esters

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(8) Chemical properties of alcohols – important reactions and uses

  • The first two alcohols, methanol and ethanol are important chemical feedstock ('starting materials') for the manufacture of many other organic chemicals e.g. esters, carboxylic acids.
    • Both ethanol and methanol are important solvents in the chemical industry because they both dissolve a wide range of compounds e.g. hydrocarbons, oils, fats, carboxylic acids. To get two solids to react it is convenient to dissolve them in a solvent to provide a reaction medium. Normally on mixing two solids you only get little or no reaction - think particle theory!
  • All alcohols 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.
  • 'Methylated Spirits' ('meths') is mostly ethanol with other chemicals added to it like methanol to make it unpalatable to drink, since pure ethanol is highly poisonous, but meths is more toxic!
    • 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 is discussed on the BIOFUELS - biogas, biodiesel, gashol, alternative fuels - hydrogen - ethanol is blended with petrol to produce a partial biofuel. Brazil, with no oil deposits, grows lots of sugar cane cheaply and this is fermented to make ethanol for fuels and other industrial uses.
  • Details of the reactions of alcohols are given below.
  • A short note on ESTERS
    • Esters are another homologous series of organic compounds (dealt with in detail on another page)
    • e.g. Ethyl ethanoate, an ester,  is formed by the reversible reaction of carboxylic acid and an alcohol e.g.
    • ethanoic acid + ethanol ethyl ethanoate + water
    • + + H2O
      • sometimes more simply written as
    • General word equation: carboxylic acid + alcohol ==> ester + water
    • This is a reversible reaction, so does not go to completion. When the equilibrium point is reached, you have also reached the point of maximum yield, and, you get about 2/3 conversion of the acid and alcohol reactants to the ester product.
    • Esters are used in perfumes and food flavourings. Lots of details in section 10b. 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 ionic salt
    • alcohol + sodium ==> an alkoxide + hydrogen gas
    • Normal 'hydrogen' gas fizzing is observed at a moderate rate, and the salt product is soluble in the alcohol itself e.g.
    • ethanol + sodium ====> sodium ethoxide + hydrogen
      • It is just the same for the other group 1 alkali metals i.e. just change the Na to K for the reactions with potassium.
    • (ii)  2C2H5OH + 2Na ====> 2C2H5ONa+ +  H2 
      • There is some similarity with the reaction of sodium with water (Alkali Metals chemistry)
      • sodium + water ==> sodium hydroxide + hydrogen

      • 2Na + 2H2O ===> 2Na+OH + H2

      • Both reactions give hydrogen gas, though the sodium reacts much faster with water. The ethoxide and hydroxide are similar because on evaporation of the unreacted ethanol or water, a solid white ionic compound is formed.

      • It can further be noted that relatively 'unreactive' alkanes do not react with sodium.

    • similarly with other alcohols ...
      •  (i)  methanol + sodium ====> sodium methoxide + hydrogen
        • 2CH3OH + 2Na ====> 2CH3ONa+ + H2
      • (iii)  propanol + sodium ==> sodium propoxide + hydrogen
        • 2CH3CH2CH2OH + 2Na ====> 2CH3CH2CH2ONa+ + H2
      • (iv)  butanol + sodium ==> sodium butoxide + hydrogen
        • 2CH3CH2CH2CH2OH + 2Na ====> 2CH3CH2CH2CH2ONa+ + 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, note that these aerobic conditions produce a very different reaction than anaerobic fermentation of sugar.
    • ethanol + oxygen ====> ethanoic acid + water
    • CH3CH2OH + O2 ===> CH3COOH + H2
    • + O2 ===>  + H2O
    • Ethanoic acid (old name 'acetic acid') is the basis of vinegar and
    • This 'natural oxidation' is used to manufacture vinegar in bulk for the food industry and domestic consumption in cooking and eating.
    • In the chemical industry ethanol is oxidised to ethanoic acid to making esters (e.g. for flavourings like ester pear drop essence as mentioned above).
    • Oxidation here, is where a molecule gains one or more oxygen atoms.
      • Check out the formulae, ethanol has one oxygen atom and ethanoic acid has two oxygen atoms.
    • This oxidation can also be done in the laboratory by heating the ethanol with a mixture of sulfuric 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.
    • Other alcohols can also be oxidised to the corresponding carboxylic acid e.g.
      • propanol + oxygen ====> propanoic acid + water
      • CH3CH2CH2OH + O2 ===> CH3CH2COOH + H2O
      • butanol + oxygen ====> butanoic acid + water
      • CH3CH2CH2CH2OH + O2 ===> CH3CH2CH2COOH + H2O
      • These reactions require special chemical reagents, you can't burn them in air to make the carboxylic acid, you would just make carbon dioxide and water on combustion!
      • The equations have been greatly simplified!
      • Some textbooks quote potassium manganate(VII) instead of potassium dichromate(VI) as the oxidising, but it doesn't work very well.
  • When burned, ethanol, like any alcohol, on complete combustion forms carbon dioxide and water
    • (i)  ethanol + oxygen ==> carbon dioxide + water
      • CH3CH2OH(l) + 3O2(g) ===> 2CO2(g) + 3H2O(l)
      • As mentioned in section 9b Fuels Survey, ethanol can be blended with petrol to fuel road vehicles.
    • Similarly, but the symbol equations are more awkward to balance  ...
      • (ii)  methanol + oxygen ====> carbon dioxide + water
        • 2CH3OH(l) + 3O2(g) ===> 2CO2(g) + 4H2O(l)
      • (iii)  propanol + oxygen ====> carbon dioxide + water
        • 2CH3CH2CH2OH(l) + 9O2(g) ===> 6CO2(g) + 8H2O(l)
      • (iv)  butanol + oxygen ====> carbon dioxide + water
        • CH3CH2CH2CH2OH(l) + 6O2(g) ====> 4CO2(g) + 5H2O(l)
      • As mentioned in section 9b Fuels Survey, ethanol can be blended with petrol to fuel road vehicles.
      • As already mentioned, ethanol is used in sprit burners where it burns much more cleanly with a blue flame - using a hydrocarbon in the same situation is more smelly and gives a more yellow smokey flame - less efficient combustion.
      • (c) doc bMeasuring the heat of combustion of alcohols
        • This can be determined using the simple copper calorimeter (diagram on the right).
        • You can compare the heat energy released by different alcohols e.g. methanol, ethanol, propanol and butanol.
        • The alcohol is poured into a little spirit burner which is then weighed.
        • The burner is placed under the copper calorimeter, which is filled with a known mass of water at a known start temperature.
        • After burning for e.g. 5 minutes, the flame is blown out and the final temperature noted.
        • The burner reweighed and the mass decrease is equal to the mass of alcohol burned.
        • From the mass of water, the heat capacity of water and the temperature change you can work out the heat energy released.
        • You can then work out the heat released per gram or per mole of alcohol.
        • Or more simply, you might just compare the mass of fuel burned to give the same temperature rise.
        • The results should show that the efficiency of an alcohol fuel increases with increase in carbon chain length of the molecule i.e. pentanol > butanol > propanol > ethanol > methanol.
        • For lots more details on the method and calculations see methods of measuring heat energy transfers in chemical reactions
  • Ethanol can be dehydrated to ethene
    • This is done by passing the alcohol vapour over heated aluminium oxide catalyst.
    • This is actually the reverse of the reaction by which ethanol is made from ethene from cracking oil.
    • ethanol ====> ethene + water
    • CH3CH2OH ====> CH2=CH2 + H2
    • ====> + H2O
    • This reaction is potentially an important source of organic chemicals e.g. plastics made by polymerising ethene, and from a renewable resource since the ethanol can be made by fermentation of carbohydrates etc.
    • It is being used in countries that do not have oil reserves but have large areas of agricultural land producing sugar cane or sugar beet that are the raw materials for the fermentation process to manufacture ethanol.
    • The ethanol, so produced, becomes an important chemical feedstock for producing lots of other chemicals including bioethanol fuel.
  • 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, they are very similar, but different molecules.
      • 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

More on the uses of some individual alcohols

A solvent. All four of these alcohols are colourless liquids and extensively used as solvents in the chemical and pharmaceutical industries. They are particularly useful solvents because they dissolve many substances that dissolve in water plus many organic compounds. This makes them very useful in the chemical synthesis, extraction and purification of many organic compounds. BUT, it should be noted, that these four alcohols are all highly flammable!

Methanol: Methanol can be used as a fuel e.g. in biofuels or blended with petrol, and methanol is cleaner burning compared to hydrocarbons (alcohol combustion equations are described above with equations). Methanol is used as an antifreeze.

Ethanol: As already mentioned - an important solvent and use in the alcohol drinks industry e.g. beers, spirits and wines. Its solvent uses include the manufacture of cosmetic formulations, pharmaceutical preparations, detergents, ink solutions and coating formulations. Also used as biofuel and in blends of petrol. Ethanol is used as an anti-freeze in windscreen de-icing formulations.

Propanol: Used as a solvent in the pharmaceutical industry and the preparation of resin and cellulose ester formulations.

Butanol: Is used in a wide range of consumer products. It is used to make butyl esters like butyl ethanoate (old name butyl acetate) which is used as solvent itself and as an artificial flavouring agent e.g. both butanol and butyl ethanoate are used in butter, cream, fruit, rum, whiskey, ice cream and ices, candy, baked goods and cordials (permitted in the US, not sure about the UK?). It is an ingredient in perfume formulations. Butanol is also used as an extractant (solvent extraction) in the manufacture of antibiotics, hormones, and vitamins. Its also a solvent for paints, coatings, natural resins, gums, synthetic resins, dyes, alkaloids, and camphor

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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 and can be recognised!  [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 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

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14-16 gcse organic chemistry, keywords and phrases: revision study notes for AQA Edexcel OCR Salters IB advanced A level chemistry for studying revision study notes for 14-16 school chemistry AQA Edexcel OCR IGCSE/GCSE 9-1 chemistry science topics modules for studying  basic chemistry of alcohols manufacture of Ethanol by fermentation physical properties of alcohols chemical reactions including combustion reaction with sodium potassium gcse chemistry revision notes igcse revising KS4 science

INDEX of Advanced A Level revision notes on the chemistry of ALCOHOLS

 Doc Brown's Chemistry 


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