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The Official Edexcel CH4 Revision Thread! (22/06/05 AM) watch

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    Okay thanks
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    hi, i've just finished born-haber cycles in this module. Is this module harder than c5?
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    Nope, although the organic section comes close to it.
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    Okay, Im doing my exam for Unit 5 this week, and Im so screwed, I need to advice on how to pass the exam resonably, you see I started falling behind in chemistry last year but my other subjects where fine, I fell so far behind that when I was in A2 I was just getting slaughtered, anyway I only need a D cuz my other subs are gonna cover the rest of my points. Basically I havnt really started revising, I got an E on Unit 4 and the teacher was surprised haha, he recommanded that I dont bother resitting and I push all my efforts into Unit 5 and Syp, he said this because I told him I am aiming for a D, plus my AS grade is a mid C, as it stands now, I am on a mid D.

    Can any1 give me some advice on pulling to average D's off, btw I am really behind in Chemistry, I hate it, I cant do it, because I didnt pay attention to the basics, and Im so lost, i just kinda of blanked it out of my mind, anyway I need 50% on unit 5, any help would be appreciated, or advice

    I am terrible at organic, and any kind of reactions, my maths skills are fine, and Im fine at learning hard facts, just cant do the chemistry.

    ANY HELP PLEASE!!!!!!!
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    I was sort of like this. My teacher was really suprised that I did Chemistry A-Level and basically had no confidence in me. It didn't help cos he's pretty poor at explaining stuff. I've improved quite a bit and hoping for a B. I've bought the Nelson Revision book which is really and summarises the whole of the syllabus in key points. Bit late now though if the exams is on Thursday. If you really don't understand it then all you can do is try and learn the reactions and hope they come up in the exam. You've left it quite late tho :confused:
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    Im abit confused of acid-base conjugate pair
    My teacher taught is something like
    base 1 + acid 2 --> base 2 + acid 1.
    While I look at the note in the net (wbateman.demon...) it said
    base 1 + acid 1 --> base 2 + acid 2
    Which one is right?
    Anyone can help me about that?
    Thanks
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    check out this link - the page has an explanation of conjugate acids/bases

    http://ibchem.com/IB/ibc/acids&bases/a&b_htm/18.1.htm

    If you think that it's not clear pm me for help
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    yes, I understand it ... but I am just confused about the number
    Code:
    Like     CH3COOH   +     NH3  ---> CH3COO-   +  NH4+
    I write:  acid 1       base2        base1       acid2
    website:  acid 1       base1        base2       acid 2
    I indicates acid 1/base 1 is conjugate pair.
    But in the website, they meant acid1/base2 as conjugate pair?
    So what should I write in the exam?
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    (Original post by BCHL85)
    yes, I understand it ... but I am just confused about the number
    Code:
    Like     CH3COOH   +     NH3  ---> CH3COO-   +  NH4+
    I write:  acid 1       base2        base1       acid2
    website:  acid 1       base1        base2       acid 2
    I indicates acid 1/base 1 is conjugate pair.
    But in the website, they meant acid1/base2 as conjugate pair?
    Yup, both right just a different way of expressing it. Numbers aren't great. Basically

    CH3COOH + NH3 ---> CH3COO- + NH4+
    acid base conj base conj acid

    You can work it out. Ethanoic acid and ammonia are obvious but since everything is in equilibrium ; the ethanoic salt will accept a hydrogen ion therefore a base. The ammonium ion ion with want to donate a hydrogen ion therefore an acid.

    I wouldnt use numbers in the exam because as you've seen theyre ambiguous, I just pair them up using arrows linking the acid/conj base together and linking the base/conj acid together and write it down aswell just to make sure.
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    thanks
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    Can I just ask why does the title on this thread say 22/06/05 AM I have the exam on thursday afternoon which is the 23/06/05 PM
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    (Original post by meawinner1)
    Can I just ask why does the title on this thread say 22/06/05 AM I have the exam on thursday afternoon which is the 23/06/05 PM
    Mine is on 23/06/05 PM as well. I really don't know, maybe it's a mistake
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    (Original post by meawinner1)
    Can I just ask why does the title on this thread say 22/06/05 AM I have the exam on thursday afternoon which is the 23/06/05 PM
    Same with me.
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    yes it was edited 4 days ago to say "BTW ITS 23rd MISTAKE"

    Im just going over the specification and there are a few things that are on it I don't know.. if anyone could help me thanks:

    What is the acid base charachteristic of Na(2)O and also Cl(2)O, and the reaction of S(2)Cl(2) that they expect us to know? Becuase my textbook says its a very complicated reaction but the exam specification says we should know it.
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    (Original post by mik1w)
    yes it was edited 4 days ago to say "BTW ITS 23rd MISTAKE"

    Im just going over the specification and there are a few things that are on it I don't know.. if anyone could help me thanks:

    What is the acid base charachteristic of Na(2)O and also Cl(2)O, and the reaction of S(2)Cl(2) that they expect us to know? Becuase my textbook says its a very complicated reaction but the exam specification says we should know it.
    Na2O is a basic oxide (Na2O has ionic bond )
    Na2O + 2HCl --> 2NaCl + H2O
    Na2O + H2O --> 2NaOH
    Cl2O is an acidic oxide (Cl2O has covalent bond)
    Cl2O + HOH --> 2HClO
    S2Cl2 is acidic
    S2Cl2 + 3H2O --> 2HCl + 2H2SO3
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    Na2O is basic and reacts with water to give sodium hydroxide
    Na2O + H2O --> 2NaOH

    Cl2O is acidic and reacts with water to give chlorate (I) acid (hypochlorous acid)
    Cl2O + H2O --> 2HClO

    S2Cl2 is hydrolysed by water to give SO2 and HCl
    2S2Cl2 + 2H2O --> SO2 + 4HCl + 3S

    this last equation may not be correct - it represents a disproportionation of the S2Cl2 on hydrolysis with water

    In terms of oxidation numbers the equation in the previous post cannot be correct (also in terms of balancing - where do the oxygens appear from?)

    Sulphur in S2Cl2 is in the oxidation state +1 (cf H2O2) it seems to me that it must disproportionate in order to make suitable stable products...
    but as I don't have the equation in a textbook a little invention was called for!
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    According to the affabus principle , the 4s subshell is filled before the 3d shell , when ions are formed the 4s electrons are lost before the 3d shell ones , why?
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    (Original post by Paxi)
    According to the affabus principle , the 4s subshell is filled before the 3d shell , when ions are formed the 4s electrons are lost before the 3d shell ones , why?
    I think you mean the 'Aufbau' principle

    You can argue all sorts of reasons for this but it always boils down to the same thing...

    ... which is that we know that this is the case by observation...

    ...and the only reason can be that the energy of the occupied 4s subshell is higher than the 3d orbitals and that the energy of the unoccupied 4s subshell is lower than that of the d orbitals.

    Why this is so seems to be because the occupation of the 4s level raises its energy (perhaps due to interelectron repulsions) with respect to the 3d subshell.
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    would that not violate conversation of energy? If you put in and get out different amounts from the 4s electrons,? Or do the energy levels of 3d electrons vary depending on whether they are filled or not?
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    surely this IS a conversation of energy!

    no, is the answer, because each process is accompanied by absorption or release of energy.

    When electrons are removed from a 4s orbital (ionisation) this requires an input of energy - it's an endothermic process (you are breaking attractions between the electrons and the nucleus)

    Besides, the Aufbau principle does not actually mean addition of electrons into orbitals, it just describes the order in which the electrons are filled moving from atom to atom in ascending atomic number - they are not actually 'built' in this way.
 
 
 
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