SPM Chemistry Form 5 Notes – Terminology and Concepts: Carbon Compounds (Part 5)

by BerryBerryTeacher

in Berry Reference (Notes)

Berry Berry Easy would like to present you with the continuation of the SPM Form 5 Chemistry notes on Carbon Compound with Part 5 in the series. To recapitulate back issues, Parts 2-4 were focused on “alkanes”, “alkenes” and their differences. So today, you’ll learn about “alcohols”, its components within the homologous series, physical properties, chemical properties (and examples) and its uses. (Be sure also to check out the misuse of alcohols) So if you are well versed with the previous four parts, it is now time to hop into part 5 of the series to learn all about alcohols. (Rather easy topic if you have master the previous four parts)

SPM Form 5 – Terminology and Concepts: Carbon Compounds (Part 5)

Non-Hydrocarbon – Alcohol

1. General formula: CnH2n + 1OH

  • Where n = 1, 2, 3 … (n = number of carbon)

2. Alcohols are non-hydrocarbons which contain carbon, hydrogen and oxygen atoms. 3. The functional group in alcohols is hydroxyl group, – OH.

Name of alcohol Molecular formula of alcohol
Methanol CH3OH
Ethanol C2H5OH
Propanol / Propan-1-ol C3H7OH
Butanol / Butan-1-ol C4H9OH
Pentanol / Pentan-1-ol C5H11OH
Hexanol / Hexan-1-ol C6H13OH
Heptanol / Heptan-1-ol C7H15OH
Octanol / Octan-1-ol C8H17OH
Nonanol / Nonan-1-ol C9H19OH
Decanol / Decan-1-ol C10H21OH

4. Physical properties of alcohol

Name Molecular formula Melting point (°C) Boiling point (°C) Physical state at 25°C
Methanol CH3OH -97 65 Liquid
Ethanol C2H3OH -117 78 Liquid
Propanol C3H5OH -127 97 Liquid
Butanol C4H7OH -90 118 Liquid
Pentanol C5H9OH -79 138 Liquid
  • Solubility in water – all members in alcohol are very soluble in water (miscible with water).
  • Volatility – all alcohols are highly volatile.
  • Colour and Smell – alcohols are colourless liquid and have sharp smell.
  • Boiling and melting points – all alcohols in general have low boiling points (78°C).

5. Chemical properties of alcohol

  • Combustion of alcohol Complete combustion of alcohol. C2H5OH + 3O2 –> 2CO2 + 3H2O (Alcohol burns with clean blue flames. Alcohol burns plenty of oxygen to produce carbon dioxide and water. This reaction releases a lot of heat. Therefore, it is a clean fuel as it does not pollute the air.) Other example: 2C3H7OH + 9O2 –> 6CO2 + 8H2O
  • Oxidation of ethanol In the laboratory, two common oxidising agents are used for the oxidation of ethanol which are acidified potassium dichromate(VI) solution (orange to green) and acidified potassium manganate(VII) solution (purple to colourless). C2H5OH + 2[O] –> CH3COOH + H2O Ethanol oxidised to ethanoic acid (a member of the homologous series of carboxylic acids – will be discussed in Part 6). Other example: C3H7OH + 2[O] –> C2H5COOH + H2O
  • Removal of water (Dehydration) Alcohol can change to alkene by removal of water molecules (dehydration). It results in the formation of a C=C double bond. CnH2n+1OH –> CnH2n + H2O C2H5OH –> C2H4 + H2O Two methods are being used to carry out a dehydration in the laboratory. a) Ethanol vapour is passed over a heated catalyst such as aluminium oxide, unglazed porcelain chips, pumice stone or porous pot. b) Ethanol is heated under reflux at 180°C with excess concentrated sulphuric acid, H2SO4. Other example: C3H7OH –> C3H6 + H2O

6. Uses of Alcohol

  • Alcohol as a solvent (cosmetics, toiletries, thinners, varnishes, perfumes).
  • Alcohol as a fuel (fuel for racing car, clean fuel, alternative fuel).
  • Alcohol as a source of chemicals (polymer, explosives, vinegar, fiber).
  • Alcohol as a source of medical product (antiseptics for skin disinfection, rubbing alcohol).

7. Misuse and Abuse

  • Depressant drug
  • Alcoholic drinks
  • Addictive drug

BerryBerryEasy would like to advise all readers not to misuse alcohol in any manner. So for Young Berries who are already driving, do not drink and drive at the same time.

{ 2 comments… read them below or add one }

March 21, 2012
March 22, 2012

Previous post:

Next post: