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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    Hey, I haven't found much in the way of online resources, but I have found a great book, it's called 'chemistry for you'. I will admit, it isn't the worlds cheapest book, but if anyone else is finding it hard to get their head around things, this really helped me. I know it has loads for edexcel as chemistry and I think A2. But not sure about other exam boards.


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    Is this correct....

    2HI + 2H2SO4 ------> H2S + I2 + S + 4H+

    ??? Thanks in advance
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    (Original post by posthumus)
    Is this correct....

    2HI + 2H2SO4 ------> H2S + I2 + S + 4H+

    ??? Thanks in advance
    Nope- you made the oxygen disappear

    8HI + H2SO4 ----> H2S + 4I2 + 4H2O ?
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    (Original post by Gnome :))
    Nope- you made the oxygen disappear

    8HI + H2SO4 ----> H2S + 4I2 + 4H2O ?
    Woop Thanks for pointing that out !

    It stats: "Hydrogen iodide reduces concentrated sulfuric acid to sulfur and hydrogen sulfide"... so just the sulfur is missing

    2HI + 2H2SO4 ----> H2S + I2 + S + 8H2O

    So could this be right ?

    Okay just realized that is no way right ! too many Hydrogen on the right
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    (Original post by posthumus)
    Woop Thanks for pointing that out !

    It stats: "Hydrogen iodide reduces concentrated sulfuric acid to sulfur and hydrogen sulfide"... so just the sulfur is missing

    2HI + 2H2SO4 ----> H2S + I2 + S + 8H2O

    So could this be right ?

    Okay just realized that is no way right ! too many Hydrogen on the right
    Just had a quick look at the textbook and chemguide (gonna marry whoever made that, seriously!)

    Iodide ions are stronger reducing agents than bromide ions are. They are
    oxidised to iodine by the concentrated sulphuric acid.

    The reduction of the sulphuric acid is more complicated than before. The
    iodide ions are powerful enough reducing agents to reduce it

    • first to sulphur dioxide (sulphur oxidation state = +4)
    • then to sulphur itself (oxidation state = 0)
    • and all the way to hydrogen sulphide (sulphur oxidation state = -2).


    The most important of this mixture of reduction products is probably the
    hydrogen sulphide.
    The reaction isn't mentioned in the textbook (the Hodder one), so I think we just need to know that I is a stronger reducing agent than Br and Cl and so results in the formation of S/H2S
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    (Original post by Gnome :))
    Just had a quick look at the textbook and chemguide (gonna marry whoever made that, seriously!)



    The reaction isn't mentioned in the textbook (the Hodder one), so I think we just need to know that I is a stronger reducing agent than Br and Cl and so results in the formation of S/H2S
    Ah okay thanks!

    I guess I should just stick to what there is it's not in the George Facer book either
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    (Original post by posthumus)
    Ah okay thanks!

    I guess I should just stick to what there is it's not in the George Facer book either
    You would need to know the reaction specifically if you were on AQA (if I remember correctly) but it isn't in our spec.
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    Hello has anyone made any revision materials on the different reactions we have to remember (Edexcel unit 2) ? e.g. reactions of halides , reactions of group 2 metals & things like what colour solutions the halogens make in different solvents. Its just I want them altogether so they are easier to memorise. If not , no worries !
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    Guys, if anyone's got something to share like the possibility of a certain question showing up in the paper or something likely to be asked in this or that way bla bla , do share thanks
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    Hey, I have just come across this question and wonder if any of you could shed some light, it's in Unit 2. 'Why does platinum speed up the reaction between ammonia and oxygen'

    Thanks in advance


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    (Original post by Cattey watty)
    Hey, I have just come across this question and wonder if any of you could shed some light, it's in Unit 2. 'Why does platinum speed up the reaction between ammonia and oxygen'

    Thanks in advance


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    Because it finds an alternative/ quicker route which lowers the activation energy required by the molecules

    I think that would be fine (for 2 marks? I assume), but in further detail;

    It has active sites on its surface that become saturated by reactants which then slowly convert it into products. This means that the rate of reaction is not altered by an increase of gaseous reactants.
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    (Original post by posthumus)
    Because it finds an alternative/ quicker route which lowers the activation energy required by the molecules

    I think that would be fine (for 2 marks? I assume), but in further detail;

    It has active sites on its surface that become saturated by reactants which then slowly convert it into products. This means that the rate of reaction is not altered by an increase of gaseous reactants.



    That's fab! Thanks very much! And yeah it's a 2 mark question so that should really be fine


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    Hello for edexcel do we need to know how to distinguish between primary, secondary and tertiary halogenoalkanes by experiment? Eg mix halogenoalkane with water to make an alcohol. Add silver nitrate solution, which gives a silver halide precipitate. Set up 3 test tubes each containing a different halogenoalkane, ethanol (as solvent) and silver nitrate solution in a water bath. Tertiary - precipitate forms instantly. Secondary - precipitate takes several seconds to form. Primary - precipitate takes several minutes to form.

    Just don't want to memorise this if I won't need it - thank you for any help you can provide.
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    (Original post by Katy1704)
    Hello for edexcel do we need to know how to distinguish between primary, secondary and tertiary halogenoalkanes by experiment? Eg mix halogenoalkane with water to make an alcohol. Add silver nitrate solution, which gives a silver halide precipitate. Set up 3 test tubes each containing a different halogenoalkane, ethanol (as solvent) and silver nitrate solution in a water bath. Tertiary - precipitate forms instantly. Secondary - precipitate takes several seconds to form. Primary - precipitate takes several minutes to form.

    Just don't want to memorise this if I won't need it - thank you for any help you can provide.
    Hi! Yeah, we need to know what they are and how to distinguish between them, my teachers have been going on about them for ages. I'm not sure if we need to know how to by experiment. I don't remember doing much on it with experiments. But our spec does say to be able to distinguish the difference of tertiary, primary and secondary by observations of a reaction 'Interpret give data and observations comparing the reactions and reactivity of primary, secondary and tertiary compounds' . Look at the spec, it's under organic chemistry in unit 2 section.

    http://www.edexcel.com/migrationdocu...-Chemistry.doc

    Hope this helps and good luck!


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    That helps a lot thank you very much good luck in the exam!
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    (Original post by geor)
    How are you guys revising the green stuff? I hate it!
    I have made some mind maps, I know this wont work for everyone but it has helped me. For example, i have made a mind map of how you you get an Aldehyde from a ketone etc. Mind maps really helped me with this, also Flash cards


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    PS Reviewer
    Can't wait to do this exam, just wanna get it out of the way.
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    (Original post by James A)
    Can't wait to do this exam, just wanna get it out of the way.
    Likewise, and preferably absolutely ace it.
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    (Original post by HarryMWilliams)
    Likewise, and preferably absolutely ace it.
    What grade you aiming for, m8?
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    (Original post by James A)
    What grade you aiming for, m8?
    An A would be great, although I will accept a high B.
 
 
 
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