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ALCOHOLS – properties and uses of ethanol

See also 9b. Biofuels, alternative fuels (now on a separate page)

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

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

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

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! The molecular structure and physical properties of ethanol. Some chemical reactions of ethanol e.g. combustion, dehydration, esterification.

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

ALL my Advanced Level Organic Chemistry revision notes for more advanced notes on alcohols

9a. 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's molecular structure
  • 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)
  • 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 in a reactor vessel (a big vat!). The yeast contains an enzyme called zymase which acts as the biological catalyst to convert sugar to ethanol in fermentation, it works best at an optimum of pH ~4. 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 ...
  • The fermentation reaction of the sugar obtained from the sugar cane or sugar cane is ...
  • glucose (sugar) == enzyme ==> ethanol + carbon dioxide
    • C6H12O6(aq) ==> 2C2H5OH(aq) + 2CO2(g) 
  • 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.
  • When the reaction is over, the 'yeast sludge' settles out and the mixture decanted off prior to distillation. Not sure if the mixture is further filtered before distillation?
  • fractional distillation diagram and theoryHow 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 upto 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 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 graphically illustrates the idea of the enzyme zymase working best at around a pH of 4. 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 upto 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 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.
  • 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.
  • 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).
    • 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 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)
    • 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.
    • This process can be carried out 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).
    • The ethene is obtained from catalytic or steam cracking reactions at high temperatures of 450oC to 900oC 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
  • 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 calculation), low due to waste carbon dioxide.
      • AND, the ethene route involves two chemical reactions ...
      • (i) Cracking: ethane ==> 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 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.
    • 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 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 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.
    • 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 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.
  • General notes on the homologous alcohols and the 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.
    • The 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.
    • 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,
  • 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 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), just like the boiling points rise in alkanes.
    • Comparison of alcohols with alkanes and water
Property alcohols

e.g. CH3CH2OH

ethanol

alkanes – hydrocarbons

e.g C6H14

hexane

water

H2O

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 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 solvents e.g. methanol and ethanol dissolves a wide variety of compounds including hydrocarbons to some extent, other alcohols, carboxylic acids and molecules used in the perfume and cosmetic industries. The important point here is that ethanol will dissolve many compounds water can't. 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.
  • 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
    • 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 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 (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
      • 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 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
    • 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
    • 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 ...
      • 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, 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
    • This 'natural oxidation' is used to manufacture vinegar in bulk for the food industry and domestic consumption in cooking and eating.
    • 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!
      • As mentioned in section 9b Fuels Survey, ethanol can be blended with petrol to fuel road vehicles.
  • Ethanoic acid (old name 'acetic acid') is the basis of vinegar and is also used in making esters (e.g. for flavourings like ester pear drop essence as mentioned above).
  • Ethanol can be dehydrated to ethene 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.
    • The ethanol, so produced, becomes an important chemical feedstock for producing lots of other chemicals.
  • 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

ALL my Advanced Level Organic Chemistry revision notes for more advanced notes on alcohols

 

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


Revision notes on ethanol physical properties chemical reactions KS4 Science GCSE/IGCSE/O level Chemistry Information on ethanol physical properties chemical reactions for revising for AQA GCSE Science, Edexcel Science chemistry IGCSE Chemistry notes on ethanol physical properties chemical reactions OCR 21st Century Science, OCR Gateway Science notes on ethanol physical properties chemical reactions WJEC gcse science chemistry notes on ethanol physical properties chemical reactions CIE O Level chemistry CIE IGCSE chemistry notes on ethanol physical properties chemical reactions CCEA/CEA gcse science chemistry (help for courses equal to US grade 8, grade 9 grade 10) science chemistry courses revision guides explanation chemical equations for ethanol physical properties chemical reactions educational videos on ethanol physical properties chemical reactions guidebooks for revising ethanol physical properties chemical reactions textbooks on ethanol physical properties chemical reactions


Teach yourself chemistry online ALPHABETICAL SITE INDEX for chemistry

Advanced Chemistry Page Index and Links

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