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Edexcel - Chemistry Unit 2 - 4 June 2013 watch

  • View Poll Results: Which topic(s) are you finding most difficult?
    Shapes of molecules and ions
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    Organic Chemistry - Alcohols and Halogenoalkanes
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    (Original post by charlieejobson)
    do we need to be able to test for halogenoalkanes?
    You might be asked to distinguist between an alcohol and haloalkane, but thats fairly simple.. You may also be asked to identify a halide.
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    (Original post by charlieejobson)
    but for example do tertiary halogenoalkanes always react the fastest with water when doing an sn1 reaction? and then primary always the fastest when doing an sn2?
    Yeah, sn2 is favoured by primary, sn1 is favoured by tertiary.
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    (Original post by geor)
    You wouldn't set out to do a "Sn1 reaction". The reaction would go by the mechanism with the lowest energy. So tertiary is always the fastest.
    This.
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    can anyone tell me all de experimental setups dat may come for sketching???
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    Why does the reducing power of a halide ion increase down group 7? Thanks
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    (Original post by HarryMWilliams)
    You might be asked to distinguist between an alcohol and haloalkane, but thats fairly simple.. You may also be asked to identify a halide.

    sorry how would i distinguish between an alcohol and a halogenoalkane?
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    (Original post by charlieejobson)
    do we need to be able to test for halogenoalkanes?
    Yup heat it with NaOH

    (halogen will be liberated)

    Add dilute nitric acid (don't think you need the reason... but it's to avoid interference from other ions or something)

    Then add silver nitrated You should know from unit 1:
    AgCl - white precipitate, soluble in dilute ammonia
    AgBr - Cream precipitate, solube only in conc. ammonia
    AgI - Yellow Precipitate, insoluble in both dilute & conc. ammonia!
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    (Original post by charlieejobson)
    sorry how would i distinguish between an alcohol and a halogenoalkane?
    I believe posthumus has explained that perfectly above.
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    (Original post by geor)
    You wouldn't be expected to draw it, but you could be asked about it! (like multiple choice question)
    oh alright then that's fine thanks!
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    Reading my textbook on preparation of 1-bromobutane from butan-1-ol. Apparently you purify the impure product with HCl to remove unreacted butan-1-ol. How does this help purify it? Doesn't it just make 1-chlorobutane? Confused :s

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    does anyone know what it means by this in the syallbus: demonstrate an understanding of why it is helpful to classify reagents (in the mechanisms part!)
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    (Original post by charlieejobson)
    does anyone know what it means by this in the syallbus: demonstrate an understanding of why it is helpful to classify reagents (in the mechanisms part!)
    So we can synthesize complex products from other reagents - example, we can make a carboxylic acid from crude oil. Just have an understanding of the whole point of classification.
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    (Original post by charlieejobson)
    does anyone know what it means by this in the syallbus: demonstrate an understanding of why it is helpful to classify reagents (in the mechanisms part!)
    An understanding of different reagents such as... free radicals, nucleophiles, electrophiles??? (if it hasn't been mentioned already)

    EDIT: Oh wait I think Harry has the better answer Each functional group gives the compound unique properties. It could also be talking about primary, secondary & tertiary.... like primary undergoes sn2, while tertiary sn1
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    have we covered free radical elimination? or is it just substitution?
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    Guys for the testing for Halogenoalkanes, some books just say add Silver Nitrate solution, whilst others say add Sodium Hydroxide/Water and THEN Silver Nitrate solution. I personally think you'd have to add the Sodium Hydroxide first, to liberate the Halide ion which would then react with the Silver Ions, BUT does silver nitrate in 'solution' means it has Water, so you can just say Silver nitrate solution?
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    (Original post by geor)
    Silver nitrate solution does mean with water, yes. Probably better to say aqueous silver nitrate though.
    Ok so to differentiate between Halogenoalkanes, you'd say add 'Aqueous Silver Nitrate'? Followed by Ammonia solution to test the percipitate itself....
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    (Original post by GCSE-help)
    Guys for the testing for Halogenoalkanes, some books just say add Silver Nitrate solution, whilst others say add Sodium Hydroxide/Water and THEN Silver Nitrate solution. I personally think you'd have to add the Sodium Hydroxide first, to liberate the Halide ion which would then react with the Silver Ions, BUT does silver nitrate in 'solution' means it has Water, so you can just say Silver nitrate solution?
    Make sure you understand what you've written there, the first "part", where you add the NaOH (in water) to the haloalkane is just converting it to an alcohol. As a consequence you are also liberating the halide ion which you can then test with the aqueous silver nitrate solution.
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    (Original post by HarryMWilliams)
    Make sure you understand what you've written there, the first "part", where you add the NaOH (in water) to the haloalkane is just converting it to an alcohol. As a consequence you are also liberating the halide ion which you can then test with the aqueous silver nitrate solution.
    Yeah I think what I said more or less explained that right? The halide ion is liberated which then reacts with the Silver ions to form a characteristically coloured percipitate.

    Thanks anyway
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    Anyone have any predictions as to what might come up?
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    (Original post by JonnyD)
    Reading my textbook on preparation of 1-bromobutane from butan-1-ol. Apparently you purify the impure product with HCl to remove unreacted butan-1-ol. How does this help purify it? Doesn't it just make 1-chlorobutane? Confused :s

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    Anyone?

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