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F334 (19/06/2013 9:00AM) - Salters Chemistry (Chemistry of Materials) Revision Thread Watch

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    (Original post by nukethemaly)
    Yeah sure,
    From graph:
    the half life for first order is constant, whereas for second order the half life increases as the reaction proceeds

    From experimental details:
    For first order, as one of the reactants is doubled, when all the others are kept the same, and the rate doubles then its FIRST ORDER
    For second order, as one of the reactants is doubled, when all the others are kept the same, and the rate quadruples then its SECOND ORDER
    I'll add that the graph for doing half lives is only if it's time against concentration :P

    Can anyone explain what is meant by "feasibility of a reaction" in the context of Ecell ?
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    Can someone clear this up:

    So amides can react with Carboxylic acids To form an ester?

    Amides can react with acyl chlorides to form an ester?

    But when you hydrolyse you always show it as a carboxylic acid/salt?

    When do you use each one or know which one to use??
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    (Original post by Tikara)
    I'll add that the graph for doing half lives is only if it's time against concentration :P

    Can anyone explain what is meant by "feasibility of a reaction" in the context of Ecell ?
    I think it means whether a reaction will take place or not
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    (Original post by hannah1994)
    Can someone clear this up:

    So amides can react with Carboxylic acids To form an ester?

    Amides can react with acyl chlorides to form an ester?

    But when you hydrolyse you always show it as a carboxylic acid/salt?

    When do you use each one or know which one to use??
    depends on the question! When you hydrolyse an ester with acid it forms an equilibrium, when you do it with an alkali it goes to completion so is usually preffered (form CI page310!)
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    (Original post by nukethemaly)
    I think it means whether a reaction will take place or not
    so like if your Ecell is positive, does that mean it will occur?
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    (Original post by hannah1994)
    Can someone clear this up:

    So amides can react with Carboxylic acids To form an ester?

    Amides can react with acyl chlorides to form an ester?

    But when you hydrolyse you always show it as a carboxylic acid/salt?
    When do you use each one or know which one to use??
    • For hydrolysis of amides: they can be done under acidic and alkaline conditions, so depending on what you use is what you'll get as a product. If you use acid, you get carboxylic acid + (substituted) ammonium ion. if you do it under alkali conditions you get an amine + carboxylate anions
    • For hydrolysis of ESTERS: if you use acidic conditions (dil. H2SO4) you get an alcohol and carboxylic acid back, but if you do it under alkali conditions (its called a SAPONIFICATION reaction), you get alcohol and a carboxylate salt.


    I'm pretty sure for amides you're only supposed to know hydrolysis.

    Amines on the other hand, react with acyl chloride to form amide.

    for esters, I think it's just:
    • alcohol + carboxylic acid
    • alcohol + acid anhydride
    • alcohol + acyl chloride
    • Phenol + benzoic acid (for example) will give phenyl benzoate + H2O
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    (Original post by Tikara)
    so like if your Ecell is positive, does that mean it will occur?
    Yep, and the higher the Ecell value you get, the stronger the reaction
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    (Original post by nukethemaly)
    Yep, and the higher the Ecell value you get, the stronger the reaction
    awesome thanks very much !
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    (Original post by Tikara)
    awesome thanks very much !
    this is also something I found useful:
    • the electrode with the more positive Ecell value will always get reduced
    • The less positive one is oxidised and hence its flipped when written so the electrons are on the right hand side!
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    (Original post by hannah1994)
    x
    So amides can react with Carboxylic acids To form an ester?
    No. To form an ester you need a carboxylic acid + alcohol, or a phenol + an acylating agent (ethanoic anhydride/ethanoyl chloride). Remember the conditions though, concentrated sulfuric acid as a catalyst; plus heating under reflux,


    Amides can react with acyl chlorides to form an ester?
    No, see above

    But when you hydrolyse you always show it as a carboxylic acid/salt?
    If you want to hydrolyse an ester, you can use dilute/aqueous alkali to produce a carboxylate salt and an alcohol.

    When do you use each one or know which one to use??
    More often than not, you use dilute/aqueous alkali to hydrolyse an ester.

    I think you may be getting confused between esters and amides. I've attached a reaction summary for this unit; hope that further clears stuff up
    Key Reactions in F334.docx
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    (Original post by abzy1234)
    So amides can react with Carboxylic acids To form an ester?
    No. To form an ester you need a carboxylic acid + alcohol, or a phenol + an acylating agent (ethanoic anhydride/ethanoyl chloride). Remember the conditions though, concentrated sulfuric acid as a catalyst; plus heating under reflux,


    Amides can react with acyl chlorides to form an ester?
    No, see above

    But when you hydrolyse you always show it as a carboxylic acid/salt?
    If you want to hydrolyse an ester, you can use dilute/aqueous alkali to produce a carboxylate salt and an alcohol.

    When do you use each one or know which one to use??
    More often than not, you use dilute/aqueous alkali to hydrolyse an ester.

    I think you may be getting confused between esters and amides. I've attached a reaction summary for this unit; hope that further clears stuff up
    Key Reactions in F334.docx
    Sorry argh yeah I don't know why i wrote that. Yeah I'm fine with esters - alcoholos/phenols.

    It's forming amides..

    how do you know whether to react an amine with a carboxylic acid or acyl chloride??
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    (Original post by abzy1234)
    So amides can react with Carboxylic acids To form an ester?
    No. To form an ester you need a carboxylic acid + alcohol, or a phenol + an acylating agent (ethanoic anhydride/ethanoyl chloride). Remember the conditions though, concentrated sulfuric acid as a catalyst; plus heating under reflux,


    Amides can react with acyl chlorides to form an ester?
    No, see above

    But when you hydrolyse you always show it as a carboxylic acid/salt?
    If you want to hydrolyse an ester, you can use dilute/aqueous alkali to produce a carboxylate salt and an alcohol.

    When do you use each one or know which one to use??
    More often than not, you use dilute/aqueous alkali to hydrolyse an ester.

    I think you may be getting confused between esters and amides. I've attached a reaction summary for this unit; hope that further clears stuff up
    Key Reactions in F334.docx
    I've just had a look at your (very helpful!!) reaction summary (thankyou!).
    One thing though...
    When phenol + acid anydride react does it not form an ester + CA?
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    (Original post by hannah1994)
    Sorry argh yeah I don't know why i wrote that. Yeah I'm fine with esters - alcoholos/phenols.

    It's forming amides..

    how do you know whether to react an amine with a carboxylic acid or acyl chloride??
    To form an amide, you always react amines with carboxylic acids or an aclyating agent (such as ethanoyl chloride). So it doesn't matter which one you choose; often in the mark scheme they'll have a range of options
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    (Original post by hannah1994)
    I've just had a look at your (very helpful!!) reaction summary (thankyou!).
    One thing though...
    When phenol + acid anydride react does it not form an ester + CA?
    Glad it helps

    Yeah it can produce a carboxylic acid as a side product, the main thing is the ester; good you spotted that!
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    (Original post by abzy1234)
    To form an amide, you always react amines with carboxylic acids or an aclyating agent (such as ethanoyl chloride). So it doesn't matter which one you choose; often in the mark scheme they'll have a range of options

    (Original post by abzy1234)
    Glad it helps

    Yeah it can produce a carboxylic acid as a side product, the main thing is the ester; good you spotted that!
    Ahh ok, thanks for your help!!!
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    sorry to sound like a fool, but is there any NMR in F334? I've not seen any on the non legacy past papers - but its in the f334 bit of storylines :/
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    (Original post by elisabethr)
    sorry to sound like a fool, but is there any NMR in F334? I've not seen any on the non legacy past papers - but its in the f334 bit of storylines :/
    Nope F335.
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    The enzymes have coo- charges but does it have NH3(positive) too or just NH2 group?Thanks
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    Why do BF3 and BCL3 have bond angles of 120 degrees and are trigonal planar shaped?
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    (Original post by EstebanK0)
    Why do BF3 and BCL3 have bond angles of 120 degrees and are trigonal planar shaped?
    You have to speak about the repulsion theory here
    • there are 3 bonding pairs of electrons
    • they each repeal one another
    • to get as far as possible in the given space
 
 
 
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