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Edexcel Chemistry Unit 4 Revision Thread watch

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    I thought we might as well come up with this thread as widowmaker has come up with the Unit 1, 2 and 3B revision thread, which did help a lot of us do better on the exams.

    So yeah u peeps can post any questions about Unit 4 on here and hope for someone to help u answer ur questions.
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    My first question:

    Why does Magnesium chloride have the formula MgCl2 instead of MgCl?
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    Because Mg is in group 2, so its Mg2+ and Cl is is group 7 so is Cl- so you need 2 Cl- for every Mg2+ ---> MgCl2
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    how is everyone learning the group 4 and period 3 reactions?
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    (Original post by violet)
    Because Mg is in group 2, so its Mg2+ and Cl is is group 7 so is Cl- so you need 2 Cl- for every Mg2+ ---> MgCl2
    I don't really agree... It's true but (according to me might I humbly add),the reason why Mg and Cl form MgCl2 and not MgCl is to do with lattice Enthalpy. The greater the magnitude of the LE, the more stable the resulting compound. The lattice enthalpy for MgCl is much smaller (in terms of magnitude not sign) than for MgCl2 and so MgCl2 is much more energetically stable...
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    (Original post by Asian cutie)
    how is everyone learning the group 4 and period 3 reactions?
    I see only one solution... drill, practice and forget and relearn and forget and relearn until you suddenly realise that you know what the product is between S2Cl2 and H2O or why SiCl4 reacts with water and not CCl4!!
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    (Original post by rieuwa)
    I don't really agree... It's true but (according to me might I humbly add),the reason why Mg and Cl form MgCl2 and not MgCl is to do with lattice Enthalpy. The greater the magnitude of the LE, the more stable the resulting compound. The lattice enthalpy for MgCl is much smaller (in terms of magnitude not sign) than for MgCl2 and so MgCl2 is much more energetically stable...
    That's probably right, I just haven't learnt that yet..
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    (Original post by violet)
    That's probably right, I just haven't learnt that yet..
    I'll admit to having learnt it last week... don't ever remember learning that in class !!! :-)
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    thanks guys.
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    Check out this site and go to chemistry > organic pathways. The downloadable word document outlines all the unit 4 organic reactions required.

    www.studyspot.moonfruit.com
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    I learnt them a few weeks ago. they are pretty easy to learn, although it will take a bit of repetition, especially with the equations showing that both lead oxides and aluminium oxide and hydroxide are amphoteric. that gets confusing, just need to remember with acid it is the same thing really and with alkali, well they're all different...

    Al(OH)3 + 3OH- ---> Al(OH)6 3- (hexahydroxoaluminate III)
    Al2O3 + 6OH- + 3H2O ---> 2Al(OH)6 3- (same^^)

    PbO + 2OH-+ H2O ---> Pb(OH)4 2- (plumbate 2 ion)
    PbO2 + 2OH----> PbO3 2- + H2O (plumbate 4 ion)

    just keep doing it, keep coming back to it and if you keep hammering away at it it will become easier and easier
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    (Original post by rieuwa)
    I don't really agree... It's true but (according to me might I humbly add),the reason why Mg and Cl form MgCl2 and not MgCl is to do with lattice Enthalpy. The greater the magnitude of the LE, the more stable the resulting compound. The lattice enthalpy for MgCl is much smaller (in terms of magnitude not sign) than for MgCl2 and so MgCl2 is much more energetically stable...
    Is that all u have to say to gain full marks or do u also have to talk about the factors which affect the lattice enthalpy.
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    (Original post by Heidi)
    Is that all u have to say to gain full marks or do u also have to talk about the factors which affect the lattice enthalpy.
    It probably depends how many marks it's worth. If a lot, then write about the factors of lattice enthalphy too.
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    (Original post by KP Nuts)
    Check out this site and go to chemistry > organic pathways. The downloadable word document outlines all the unit 4 organic reactions required.

    www.studyspot.moonfruit.com

    thanks for that. That's really gd! I'll give ya a rep for this
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    (Original post by violet)
    It probably depends how many marks it's worth. If a lot, then write about the factors of lattice enthalphy too.
    it's worth 3 marks. So im not sure whether I should include the factors of LE in my answer.
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    (Original post by Heidi)
    it's worth 3 marks. So im not sure whether I should include the factors of LE in my answer.
    If i were you then I would just write them anyway. Cos.. if its not part of the answer then you haven't lost any marks, but if it is and you don't put it down then you do!
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    (Original post by violet)
    If i were you then I would just write them anyway. Cos.. if its not part of the answer then you haven't lost any marks, but if it is and you don't put it down then you do!
    yeah i guess i betta do that then. Definitely don't wanna risk losing marks! How is ur revision going?
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    (Original post by Heidi)
    yeah i guess i betta do that then. Definitely don't wanna risk losing marks! How is ur revision going?
    It's... going! The thing is i work much better under pressure like 2 days before an exam.. And I have no exams this week so I find it hard to revise!
    I should be doing Biology now
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    "there is no substitute to hardwork"
    little motivational qoute 4 u there Do Bio rev! THINK OF THAT A U'LL GET!!
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    (Original post by violet)
    It's... going! The thing is i work much better under pressure like 2 days before an exam.. And I have no exams this week so I find it hard to revise!
    I should be doing Biology now
    hehe I work better under pressure as well.
    I also have to revise for bio. It's really unfair how the chem and bio exam r so close together! Oh well. Which board are u with? Im with AQA?
 
 
 
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