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    (Original post by Daniel__)
    General question, in regards to systematic naming how do you know which element the roman numerals refers to as a rule of thumb? Also, can the roman numerals represent a negative oxidation number?
    I dont think roman numerals ever represent a negative oxidation number, but definitely not for this exam. Could you give me an example of a oxidation number question and I would explain it better that way thanks
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    I have a good question for you guys to tackle


    State the bond angle of C(CH3)3Si and explain why (4 marks)
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    (Original post by sladyy96)
    Does anyone know if we have to know how Carbonic Acid is formed (plus equations)?
    no thats only for biology.
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    (Original post by Danny786)
    http://quizlet.com/23659907/f321-flash-cards/

    Check this out, really helpful, someone posted it below
    Hahaha you're welcome
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    (Original post by sheepshap)
    what definitions do we need to know?
    The definitions they love asking for are ionisation energies, relative atomic/isotopic mass, a salt, water of crystallisation, an orbital and isotopes.
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    Someone please look at question 2b(ii) on May 2011 paper :http://www.ocr.org.uk/Images/65868-q...and-groups.pdf

    if you look at the markscheme: http://www.ocr.org.uk/Images/60301-m...roups-june.pdf
    the answer is surely wrong as CaO from thermal decomposition is solid product and CaCl2 is aq hence the difference is Solid diappears and both produce CO2 hence thats a similarity its Urgent!!!
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    (Original post by otrivine)
    I have a good question for you guys to tackle


    State the bond angle of C(CH3)3Si and explain why (4 marks)
    I think you typed the question up wrong. In that example carbon would be bonded to 5 atoms (3 hydrogens, silicon and the other carbon) which is impossible.
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    (Original post by theCreator)
    It's only diatomic in if it's a group 6, 7 element and nitrogen in group 5. Since they can get their full shells by bonding with each other, whether it be a single, double or triple bond.
    Thankyou!


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    theCreator, you are definitely a chemistry genius!
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    (Original post by JimmyA*)
    I'm guessing they'll put a hard titration type question, as the January report say's all the maths questions were answered very well and were too easy.
    I'm fine with those as they'll never catch me out, could they ask us how the procedure taken to do a titration though? What other things do you think will arise?
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    (Original post by drplease)
    Someone please look at question 2b(ii) on May 2011 paper :http://www.ocr.org.uk/Images/65868-q...and-groups.pdf

    if you look at the markscheme: http://www.ocr.org.uk/Images/60301-m...roups-june.pdf
    the answer is surely wrong as CaO from thermal decomposition is solid product and CaCl2 is aq hence the difference is Solid diappears and both produce CO2 hence thats a similarity its Urgent!!!
    No you misread the question. Test tube A was heated, thermally decomposing the CaCO3 to make CaO as you said. But test tube B you did NOT heat it, so you still have the CaCO3. Therefore when you added both the solids to the acid they dissolved, but on the CaCO3 reaction produced a gas.
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    (Original post by theCreator)
    I think you typed the question up wrong. In that example carbon would be bonded to 5 atoms (3 hydrogens, silicon and the other carbon) which is impossible.
    so made a typo meant


    C(CH3)3Si
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    (Original post by theCreator)
    I think you typed the question up wrong. In that example carbon would be bonded to 5 atoms (3 hydrogens, silicon and the other carbon) which is impossible.
    No actually my question is correct
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    (Original post by jo7777)
    theCreator, you are definitely a chemistry genius!
    I wish ahah but thank you I hope to do it at uni.
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    Can someone help me out? Towards the end of the january 2012 paper it asks for the bond angle and shape of a "H-N-H" molecule that came from hydrazine and im not sure why the bond angle is 107.5 degrees and pyramidal. Thanks.
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    (Original post by otrivine)
    No actually my question is correct
    If it is from a past paper could you link me it please. But if not then I have no idea how that molecule would even look bonded.
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    (Original post by blackstarz)
    Can someone help me out? Towards the end of the january 2012 paper it asks for the bond angle and shape of a "H-N-H" molecule that came from hydrazine and im not sure why the bond angle is 107.5 degrees and pyramidal. Thanks.

    I apologise to everyone else for seemingly spamming the forum by answering questions.

    It is because the entire molecule is (NH2)-(NH2) so the Nitrogen in this case is bonded to the other nitrogen and 2 hydrogens. This means the nitrogen has a lone pair and 3 bond pairs which makes it assume the trigonal pyramid shape.
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    (Original post by blackstarz)
    Can someone help me out? Towards the end of the january 2012 paper it asks for the bond angle and shape of a "H-N-H" molecule that came from hydrazine and im not sure why the bond angle is 107.5 degrees and pyramidal. Thanks.
    Nitrogens got a lone pair of electron and it should have 3 atoms of hydrogen around n but it doesn't so I can explain but also can't explain


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    (Original post by theCreator)
    If it is from a past paper could you link me it please. But if not then I have no idea how that molecule would even look bonded.
    I made the question myself but the bond angle would be simply a tetrahedral because C(CH3)Si you can see the carbon atom is attached to 3 methyl groups and a silicon molecule and hence 4 bonding pairs and no lone pairs----> tetrahedral (109.5) because of the electron pair repulsion as into maximise separation and minimise repulsion
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    (Original post by theCreator)
    I apologise to everyone else for seemingly spamming the forum by answering questions.

    It is because the entire molecule is (NH2)-(NH2) so the Nitrogen in this case is bonded to the other nitrogen and 2 hydrogens. This means the nitrogen has a lone pair and 3 bond pairs which makes it assume the trigonal pyramid shape.
    how do you know it's (NH2)-(NH2)? does the question show you (is there a diagram)?
    or does it say it has hydrogen bonding?
 
 
 
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