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Chemistry: Post your doubts here!

Discussion in 'International A And AS Level' started by XPFMember, Sep 29, 2011.

  1. AAestar

    AAestar

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    When reacted with a small quantity of water, SiCl4 produces an oxychloride X, SixClyOz.
    The mass spectrum of X shows peaks at mass numbers of 133, 149, 247, 263 and 396.
    (You should assume that the species responsible for all these peaks contain the
    16O, the 35Cl and the 28Si isotopes only.)
    (i) Use these data to deduce the molecular formula of X

    This is from j10,p42, Q3d.
    http://www.xtremepapers.com/CIE/Interna ... _qp_42.pdf

    It would be tedious to find it one by one just to reach the value 396. Is there any simple method to solve this question?
     
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  3. destined007

    destined007

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    You have to find the fragments formulae in part ii so why not do it in part i and make your life easier? That way you will be able to part i quickly and because you have already calculated fragments formulae in part i you just have to copy them in part ii,
     
  4. destined007

    destined007

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    Re: help in chemistry questions...

    methanol is CH3OH. you have written the formula of methanal HCHO. Confirm which one is in the question. Same goes for part 5, ethanol is CH3CH2OH. You have written ethanal CH3CHO. Confirm these and all the other parts.
     
  5. babycry

    babycry

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    Which of the enthalpy changes of the following reactions can only be obtained by application of
    Hess’ Law?
    1 The hydration of anhydrous copper sulphate to form crystals of CuSO4.5H2O.
    2 The formation of methane from its elements.
    3 The combustion of glucose, C6H12O6.
    can u plz help with this one ?
     
  6. OakMoon!

    OakMoon! XPC Moderator Staff Member

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    2 and 3 are correct.
     
  7. OakMoon!

    OakMoon! XPC Moderator Staff Member

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    Your concept of successive ionistation energies is probably not correct. There is a sharp rise in ionisation energy when the shell number or the quantum number changes, and the difference b/w 5 and 6 is quite large to show that 6th I.E is of an electron from the next shell. So this atom has 5 outer shell electrons, and hence it is in group 5.
    The changes in successive I.E from 1st to 2nd and 2nd to third, that you are talking about, are the normal increase in I.E as one electron has already been removed.
     
  8. babycry

    babycry

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    you are wrong.. 1 and 2 are correct :D its because when hydrating the CuSO4, not all the CuSO4 dissolves, so its not 100% correct.

    2 is correct because The reaction 4C + 2H2 is not possible so we can only use Hess's Law

    3 is wrong because we can completely burn 1 mol of glucose and measure the enthalpy changes..

    :D:D
     
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  9. OakMoon!

    OakMoon! XPC Moderator Staff Member

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    So if you know the answer and the explanation, why would you ask? :O
     
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  10. anahita16

    anahita16

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    helloo
    um...how do u guys keep such a peaked interest in chemistry? I've this problem with chemistry and physics. Figured it wud be better if i asked this question in a thread where the chem people will visit most! i've a serious problem with electrochemistry :unknown: how do i get this concept in my head?
     
  11. ArthurBonZavi

    ArthurBonZavi

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    Keep referring your book until you clear a certain topic. If you cannot understand from the book, target internet resources. After you are through with all the chapters, practise all the past papers.
     
  12. babycry

    babycry

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    I asked then I checked my Chemistry MCQ book which helped me out.. thanks for the reply man.. i really appreciate it

    eid mubarak by the way :)
     
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  13. dsowner

    dsowner

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    Hey guys. Is there a list somewhere that states which complex ion colours we are supposed to memorise and which we can ignore? There are literally dozens and if I remembered correctly, Cambridge never stated we had to memorise all of them.
     
  14. AAestar

    AAestar

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    How do we identify which E cell equation to use? Some, for example Fe, has 3 E cell equations.Which one should i choose? Depending on what type of criteria?
     
  15. Xthegreat

    Xthegreat

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    if you are in A2, then u only need to memorise for copper.
     
  16. memyself15

    memyself15

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    it depends on the question.
     
  17. ALevelstudent

    ALevelstudent

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  18. Emily793

    Emily793

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    hey guys can you confirm what topics are to be revised for chemistry p42???
     
  19. sweetiepie

    sweetiepie

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    check out these may help u :)
     

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  20. Emily793

    Emily793

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    are these the only topics to be revised for p4? or should i revise the whole bunch of topics found in syllabus??
     
  21. sweetiepie

    sweetiepie

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    whole bunch of topics found in syllabus?? :)
     

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