O Level – Chemistry

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  • #3810

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    Petroleum

    1. Petroleum is a non-renewable resource and there is only a limited amount of petroleum in the Earth.

    2. Moet petroleum is used as fuel. Only a small amount is used as feedstock to make useful petrochemicals.

    3. Gasohol is an alternative energy sources used as a fuel in motor vehicles.

    4. Biogas is also used as an alternative energy source. It contain about 50% ethane.

    5. Hydrogen can also be used as a fuel for cars.

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    #3868

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    Important Definitions – Alkanes & Alkenes

    1. Saturated hydrocarbon are compounds containing only carbon and hydrogen and having single bonds between carbon atoms.

    2. Unsaturated hydrocarbon are compounds containing only carbon and hydrogen and having double bonds between carbon atoms.

    3. Alkane series has a general formula CnH2n+2

    4. Alkenes series has a general formula CnH2n

    5. Structural formula is the chemical formula that shows how the atoms are joined together in a molecue.

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    #4118

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    Important Definitions – Alkanes & Alkenes

    6. Isomerism is the existence of two or more organic compounds with the same molecular formula but different structural formulae. These different compound called isomers.

    7. A substitution reaction is a reaction in which an atom (or a group of atoms) in an organic molecule is replaced by another atom ( or group of atoms)

    8. An addition reaction is a reaction in which an unsaturated organic compound combines with another substance to form a single product.

    9. Cracking is a process in which a large hydrocarbon molecules are broken down into smaller molecules.

    10. Polyunsaturated compounds are organic molecules that contain more than c=c bond.

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    #4221

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    Alkanes

    1. Saturated hydrocarbon are hydrocarbons with only single bonds between carbon atoms.

    2. Unsaturated hydrocarbons are hydrocarbons with one or more double bond or triple bond between carbon atoms.

    3. The alkanes are saturated hydrocarbons with the general molecular formula CnH2n+1 where n = 1, 2, 3, ……

    4. Alkanes contain only single bonds between carbon atoms. Each carbon atom in an alkane molecule uses all its valence electrons in forming single bonds with four other atoms.

    5. First four members of the alkane
    Methane CH4
    Ethane C2H6
    Propane C3H8
    Butane C4H10

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    #4317

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    Alkenes

    1. Alkenes are unsaturated hydrocarbons that contain one or more carbon-carbon double bond

    2. The general formula of alkenes with one double bond is CnH2n

    3. Naming of alkenes
    Ethene C2H4
    Propene C3H6
    Butene C4H8

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    #4363

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    Isomerism

    1. Isomerism is where two or more organic molecules have the same molecular formula but different structural formula. These different molecule are called isomers.

    2. Isomers have different melting and boiling points

    3. Methane, ethane and propane do not have isomers.

    4. Butane has two isomers
    – Butane
    – Methylpropane

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    #4442

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    Chemical Properties of Alkenes Part 1

    1. The functional group of alkenes is the carbon-carbon double bond (C=C).

    2. Alkenes are more reactive than alkanes because of the presence of the double bond.

    3. The combustion of alkenes produces carbon dioxide and water

    4. Alkenes produce more soot than alkanes when they burn in air because a relatively higher percentage of carbon than the alkanes with the same number of carbon atoms.

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    #4444

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    Chemical Properties of Alkenes Part 1

    1. The functional group of alkenes is the carbon-carbon double bond (C=C).

    2. Alkenes are more reactive than alkanes because of the presence of the double bond.

    3. The combustion of alkenes produces carbon dioxide and water

    4. Alkenes produce more soot than alkanes when they burn in air because a relatively higher percentage of carbon than the alkanes with the same number of carbon atoms.

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    #4495

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    The Manufacture of Alkenes by Cracking

    1. Alkenes are obtained by the cracking of petroleum fractions, such as the naphtha fraction.

    2. Cracking is the process in which large hydrocarbon molecules are broken down into smaller molecules.

    3. When an alkane molecule is cracked, a mixture of short-chain alkanes, alkenes and hydrogen are formed.
    Example:
    When the alkane C13H28 in naphtha is cracked, it is broken up into smaller alkane and alkene molecules

    3. When an alkane molecule is cracked, a mixture of short-chain alkanes, alkenes and hydrogen
    are formed.

    Example:
    When the alkane C13H28 in naphtha is cracked, it is broken up into smaller alkane and alkene molecules

    4. The conditions used for cracking
    (a) In industries, cracking is carried out by passing the petroleum fraction over the catalyst at high temperature. The process is called catalytic cracking.
    (b) The conditions for catalytic cracking are:
    • Temperature: 600°C
    • Catalyst: Silicon(IV) oxide, SiO2, or aluminium oxide, A/203

    5. In the school laboratory, catalytic cracking can be carried out using the apparatus as shown in the following diagram.

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    #4548

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    Key definitions – Alcohols and Carboxylic Acids

    1. Alcohols are organic compounds that contain the hydroxyl (—OH) group.

    2. Fermentation is the process of converting sugars into ethanol and carbon dioxide, catalysed by the enzymes in yeast.

    3. Carboxylic acids are organic compounds that contain the carboxyl (—COOH) group.

    4. Esters are organic compounds produced from the reactions between carboxylic acids and alcohols.

    5. Esterification is the reaction between a carboxylic acid and an alcohol to produce an ester and water.

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    #4633

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    Macromolecules – IMPORTANT DEFINITIONS

    1. A macromolecule is a large molecule in which there is a very large number of atoms joined together by covalent bonds.

    2. A polymer is a large molecule made up of many repeat units joined together by covalent bonds.

    3. A monomer is the starting material for making a polymer.

    4. Polymerisation is the process of joining up of many small molecules (monomers) to form a long-chain molecule (polymer).

    5. Addition polymerisation is a reaction in which monomers join together to form a large molecule (polymer) as the only product.

    6. Condensation polymerisation is a reaction in which monomers join together to form polymers with the elimination of small molecules.

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    #4702

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    Macromolecules

    1. A macromolecule is any long-chain molecule that contains hundreds or thousands of atoms, joined together by covalent bonds.

    2. A macromolecule is formed by linking together many small repeating units known as monomers.

    3. The process of joining together a large number of small molecules (monomers) to form a macromolecule is called polymerisation. The macromolecule formed is called a polymer.

    5. Synthetic macromolecules, such as plastics, are now manufactured on a large scale.

    6. Different macromolecules have different units and different linkages.

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    #4758

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    Macromolecules

    1. A macromolecule is any long-chain molecule that contains hundreds or thousands of atoms, joined together by covalent bonds.

    2. A macromolecule is formed by linking together many small repeating units known as monomers.

    3. The process of joining together a large number of small molecules (monomers) to form a macromolecule is called polymerisation. The macromolecule formed is called a polymer.

    4. Macromolecules are common in living things.
    For example, the organic compounds, proteins and starch, found in animals and plants are examples of natural macromolecules.

    5. Synthetic macromolecules, such as plastics, are now manufactured on a large scale.

    6. Different macromolecules have different units and different linkages.

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    #4817

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    Addition Polymerisation

    1. Addition polymerisation occurs when monomer units join together without losing any molecules or atoms.

    2. Poly(ethene)
    (a) At high pressure and temperature and in the presence of a catalyst, ethene undergoes addition polymerisation to form a long-chain molecule, poly(ethene).

    (b) Ethene is called the monomer and poly(ethene) is called the polymer.

    (c) Uses of poly(ethene)
    Poly(ethene) is widely used as plastic bags, plastic bottles and cling films for wrapping food.

    Condensation Polymerisation

    1. In condensation polymerisation, small molecules such as water, are eliminated when monomers join together to form a polymer.

    2. For condensation polymerisation to occur, each monomer must have two reactive groups. The polymer chain is formed by the removal of water molecules.

    3. There are two main groups of condensation polymers: polyamides and polyesters.

    4. Nylon: a polyamide
    (a) Nylon is made from two different monomers:
    • Dicarboxylic acid (a molecule with two -COOH groups)
    • Diamine (a molecule with two -NH2 groups)
    (b) When the two monomers combine, the polymer, nylon, is formed and water molecules are eliminated.

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    #4875

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    Condensation Polymerisation

    1. In condensation polymerisation, small molecules such as water, are eliminated when monomers join together to form a polymer.

    2. For condensation polymerisation to occur, each monomer must have two reactive groups. The polymer chain is formed by the removal of water molecules.
    Example:
    Dicarboxylic acid (two -COOH groups) + diamine (two -NH2 groups)
    HOOC – X – COOH + NH2 – Y – NH2 polyamide + H2O
    dicarboxylic acid diamine (e.g. nylon) water

    3. There are two main groups of condensation polymers: polyamides and polyesters.

    4. Nylon: a polyamide
    (a) Nylon is made from two different monomers:
    • Dicarboxylic acid (a molecule with two -COOH groups)
    • Diamine (a molecule with two -NH2 groups)
    (b) When the two monomers combine, the polymer, nylon, is formed and water molecules are eliminated.

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