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(c) doc bDoc Brown's GCSE/IGCSE KS4 science-CHEMISTRY Revision Notes

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

10. Carboxylic acids and esters

Carboxylic acids are a group of organic compounds which have weakly acidic properties. The react with bases/alkalis to for salts and release carbon dioxide from carbonates. They react with alcohols (another organic series of compounds) to form organic compounds called esters which are used as solvents and components in perfumes and food flavourings.

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

10. CARBOXYLIC ACIDS and ESTERS - other families of organic compounds

We find members of the homologous series called carboxylic acids in fruits and in vinegar and many in fragrances and food additives as carboxylic acid derivatives called esters. ((c) doc b ester preparation and uses of esters).

  • Carboxylic acids form another homologous series and have the functional group -COOH.
  • The structures of the first three members are given below: Names end in ...oic acid.
    • Advanced Chemistry Page Index and Linksmethanoic acid (old name 'formic acid')
      • or or
    • ethanoic acid (old name 'acetic acid', in vinegar)
      • or or
    • propanoic acid (old name 'propionic acid')
      • or or
  • Vinegar contains ethanoic acid (old name 'acetic acid')
    • Ethanoic acid can be manufactured on a large scale by oxidising the alcohol ethanol.
    • It is used as a preservative and in food flavourings.
  • Ethanoic acid is used in the manufacture of the fibre, acetate rayon.
  • Citrus fruits like oranges and lemons and many soft drinks contain the tri-carboxylic acid citric acid.CITRIC ACID and contribute to the 'tarter' or 'sour' taste of fruit. The molecule contains three acidic carboxylic acid groups -COOH.
    • Citric acid is a natural preservative (E330 on food labels) and is found in the largest quantities in lemons, limes and grapefruit. It is an anti-oxidant. Metal salts from citric acid, i.e. citrates, are used in dietary supplements to deliver trace metal minerals in a biologically available/absorbable chemical form.
    • Citric acid can be used in baking powder to react with sodium bicarbonate giving the raising action from carbon dioxide gas formation. The same combination can be used to give the fizzy drink effect in medicines like ant-acid stomach powders.
  • Aspirin is a carboxylic acid. Aspirin is a drug used for pain relief and is taken regularly by those at risk from heart attacks (see also (c) doc b Drugs).
  • Ascorbic acid (vitamin C) is another carboxylic acid and is present in fresh fruit and vegetables and is vital for good health AND the body cannot synthesise it, so you must eat fruit and vegetables regularly!
    • A lack of vitamin C can cause the disease scurvy. The symptoms of scurvy are skin sores, spongy gums and bleeding from mucous membranes. This is one example of malnutrition diseases caused by a vitamin deficiency in a diet.
  • Carboxylic acids are weak acids, typically solutions are around pH 3 (yellow-orange-pink with universal indicator).
    • Advanced Chemistry Page Index and LinksThey are called weak acids because only a few % of the molecules in aqueous ionise to release protons (hydrogen ions, H+).
      • e.g. for ethanoic acid (vinegar)
      • 98% CH3COOH(aq) <==> CH3COO-(aq) + H+(aq) 2%
    • [(c) doc b see theory of acids and bases]
  • They react and are neutralised by bases (insoluble or soluble - alkalis and carbonates) ... with examples ...
    • metals react to form salts and hydrogen e.g.
      • ethanoic acid + magnesium ==> magnesium ethanoate + hydrogen
      • 2CH3COOH + Mg ==> (CH3COO)2Mg + H2
    • alkalis (soluble bases) react to form a carboxylic acid salt and water  e.g.
      • ethanoic acid + sodium hydroxide ==> sodium ethanoate + water
      • CH3COOH + NaOH ==> CH3COONa + H2O
      • OR ethanoic acid + potassium hydroxide ==> potassium ethanoate + water
      • CH3COOH + KOH ==> CH3COOK + H2O
    • insoluble bases dissolve and react to form salt and water e.g.
      • zinc oxide + ethanoic acid ==> zinc ethanoate + water
      • ZnO + 2CH3COOH ==> (CH3COO)2Zn + H2O
    • carbonate and hydrogencarbonate bases to produce a carboxylic acid salt, water and carbon dioxide  e.g.
      • ethanoic acid + sodium hydrogen carbonate ==> sodium ethanoate + water + carbon dioxide
      • CH3COOH + NaHCO3 ==> CH3COONa + H2O + CO2
      • OR ethanoic acid + sodium carbonate ==> sodium ethanoate + water + carbon dioxide
      • 2CH3COOH + Na2CO3 ==> 2CH3COONa + H2O + CO2
      • OR propanoic acid + sodium carbonate ==> sodium propanoate + water + carbon dioxide
      • 2CH3CH2COOH + Na2CO3 ==> 2CH3CH2COONa + H2O + CO2
    • aqueous ammonia solution forms ammonium salts e.g.
      • methanoic acid + ammonia ==> ammonium methanoate
      • HCOOH + NH3 ==> HCOONH4
      • ethanoic acid + ammonia ==> ammonium ethanoate
      • CH3COOH + NH3 ==> CH3COONH4
      • Strictly speaking, ammonium hydroxide doesn't really exist, but in older texts you will find these reactions written in this way e.g.
        • propanoic acid + ammonium hydroxide ==> ammonium propanoate + water
        • CH3CH2COOH + NH4OH ==> CH3CH2COONH4 + H2O
  • Advanced Chemistry Page Index and LinksESTERS: Carboxylic acids react with alcohols to form members of another homologous series called esters. Concentrated sulphuric acid acts as a catalyst in this reaction.
    • + + H2O
      • sometimes more simply written as
      • CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O
    • For more details see the (c) doc b preparation & formation of ethyl ethanoate and other esters in section 9 for lots more details.
    • Structures of other esters made from ethanoic acid:
      • (c) doc bmethyl ethanoate using methanol, and
      • (c) doc b propyl ethanoate from using propan-1-ol (n-propyl alcohol).
    • and what would the structure of their original alcohols be and what would the structure of butyl ethanoate be?
  • Esters occur widely in nature and are usually sweet/pleasant smelling liquids and widely used as fragrances (e.g. perfumes) and food flavourings. Natural substances are used in many cosmetics but many mixtures contain synthetic organic compounds.
    • Examples of plant ester sources:
      • Lavender oil essence is distilled from the lavender plant
    • Examples of flavouring esters:
      • Pear drop sweet essence is an ester.
    • Factors affecting perfume design e.g. using esters:
      • Designing a perfume - several issues to address by way of design factors.
      • The perfume needs to be a mixture of compounds to give a prolonged perfumery effect.
      • The perfumer chemist has to design the mixture to give a particular fragrance which includes ...
        •  the top note - the first fragrant molecule to be released,
        • and the low note, the last molecule to be vapourised.
    • -

Advanced Chemistry Page Index and Links

 

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


Revise KS4 Science GCSE/IGCSE/O level Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel 360Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science WJEC/CBAC GCSE science-chemistry CCEA/CEA GCSE science-chemistry (and courses equal to US grades 8, 9, 10)

 

Advanced Chemistry Page Index and Links
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