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    I need help with part c(ii) and d and e.Thanks!

    Q) Octane is a hydrocarbon which is a component of gasoline.

    (a)What is the molecular formula of octane?

    (b)Draw the skeletal structure of octane.

    (c)Isooctane is an isomer of octane.
    (i)Draw the structural formula of isooctane
    (ii)Why is isooctane a better fuel than octane.

    (d)A series of tests are performed on octane.What if anything would you observe in each of the following?

    (i)Addition of chlorine
    (ii)Addition of aqueous bromine
    (iii)Addition of excess oxygen(combustion)
    (iv)Cracking

    (e)Why are the isomers of octane flammable?
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    (c) ii. Branched alkanes have a higher octane number, therefore they are less volitile and less likely to "knock" or auto ignite.

    Sorry, can't help you with the others, they're not part of the my syllabus.
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    (c) ii = Because in a branched molecule, there are less Intermolecular forces between the molecule, and this means it would have a lower boiling point in comparison to its straight chain molecule. So it would burn more readily, and therefore be a better fuel.

    Addition of Chlorine and Bromine would be Electrophillic Substitution, and therfore would form a HCl or HBr molecule..?
    Combustion would form CO2 and H2O and you just balance it out.
    Cracking would form 2 seperate molecules, one of them would be an alkene!

    Hope that has helped!
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    (Original post by Shawn44)

    (d)A series of tests are performed on octane.What if anything would you observe in each of the following?

    (i)Addition of chlorine

    Needs UV light for a free radical substitution reaction to take place. Otherwise, nothing will happen.


    (ii)Addition of aqueous bromine

    Nothing. (An alkene would de-colourise Bromine water).

    (iii)Addition of excess oxygen(combustion)

    Burns to produce CO2 and H2O.

    (iv)Cracking

    Forms smaller hydrocarbon chains.
    .......
 
 
 
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