SPM Chemistry

Hydrocarbon

user

Hydrocarbon

MUST Remember!
Hydrocarbons are organic compounds that contain only carbon and hydrogen.
Saturated Hydrocarbon
      1. Hydrocarbon is a compound made out of the elements carbon and hydrogen only.
      2. Examples of hydrocarbon are alkane, alkene and alkyne. 
      3. Hydrocarbons can be divided into two groups:
        1. saturated hydrocarbon
          Saturated hydrocarbons are hydrocarbons where all its carbon atoms are tied to each other through single covalent bond only. Examples: alkanes
        2. unsaturated hydrocarbon
          Unsaturated hydrocarbons are hydrocarbons which contain at least one double covalent bond among its carbon atoms. Examples: alkenes
    Unsaturated Hydrocarbon
    1. Ethanol ( C2H5OH ), ethanoic acid (CH3COOH), metal methanoate (HCOOCH3), chloromethane (CH3Cl) and others are not hydrocarbons because the molecule contains other elements such as chlorine or oxygen other than carbon and hydrogen.

    MUST Know!

    • Saturated – All single bond between carbons 
    • Unsaturated – Has at least one double/triple bond between carbons

    Comparing Saturated and Unsaturated Hydrocarbon

    Saturated HydrocarbonUnsaturated Hydrocarbon
    CombustionProduce less sootProduce more soot
    Reaction with bromine waterThe brown colour of bromine remain unchangedDecolourise the brown colour of bromine
    Reaction with potassium manganate(VII) solutionThe purple colour of potassium manganate (VII) solution remain unchangedDecolourise the purple colour of potassium manganate (VII) solution

    Sources of Hydrocarbon:

    The main sources of hydrocarbons are
    1. Coal
    2. Natural gas
    3. Petroleum
    Download the printable version of this note.

    Combustion of Hydrocarbon

    All hydrocarbons undergo combustion with oxygen to produce carbon dioxide (or carbon monoxide/carbon) and water. There are 2 types of combustion:
    1. Complete combustion – organic compounds burn completely which form CO2 and H2O
    2. Incomplete combustion– organic compounds burn with limited supply of O2 which form C (soot), CO, CO2 and H2O.

    Example

    Complete combustion

    C2H6 + 7/2 O2 → 2CO2 + 3H2O

    C3H6 + 9/2 O2 → 3CO2 + 3H2O

    Incomplete combustion

    C2H6 + 5/2 O2 → 2CO + 3H2O

    C2H6 + 3/2 O2 → 2C + 3H2O


    C3H6 + 3O2 → 3CO + 3H2O

    C3H6 + 3/2 O2 → 3C + 3H2O

    Note:

    1. The soot from the combustion of a hydrocarbon depends on the percentage of carbon it contains.
    2. Higher carbon percentage in the hydrocarbon molecule will result sootier flame.