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F334 (19/06/2013 9:00AM) - Salters Chemistry (Chemistry of Materials) Revision Thread Watch

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    (Original post by tsr1)
    The enzymes have coo- charges but does it have NH3(positive) too or just NH2 group?Thanks
    Look at page 26 of the official revision guide
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    (Original post by EstebanK0)
    Why do BF3 and BCL3 have bond angles of 120 degrees and are trigonal planar shaped?
    Boron is group 3 so 3 outer electrons
    so it shares one with each Fluorine/Chlorine molecule to make 3 bonds
    there are hence no lone pairs on the boron

    3 areas of electron density = 120 degrees
    as there are three molecules (attached to the B) it is trigonal planar

    nukethemaly above has mentioned the points that get the marks :P
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    (Original post by nukethemaly)
    You have to speak about the repulsion theory here
    • there are 3 bonding pairs of electrons
    • they each repeal one another
    • to get as far as possible in the given space
    I understand that. But, Boron doesn't achieve an inert gas configuration as each Cl atom shares one electron with B?
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    I'm so nervous for tomorrow
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    Hi

    F334 JAN 2013 - Last question. how do you calculate rate of disappearance?!?!
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    (Original post by :)ella)
    Does anyone have a copy of the Jan 13 paper?

    I'm so nervous for tomorrow
    January Paper.pdf
    January MS.pdf

    Don't worry! It's only natural to get exam nerves now; best thing to do is go over you notes, finish off them past papers; so you can gain confidence for tomorrow. Try your best, and you'll get what you put in
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    (Original post by abzy1234)
    Attachment 227995
    Attachment 227996

    Don't worry! It's only natural to get exam nerves now; best thing to do is go over you notes, finish off them past papers; so you can gain confidence for tomorrow. Try your best, and you'll get what you put in
    thanks wsa just looking for this :P

    wait it's not workinng
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    (Original post by Tikara)
    thanks wsa just looking for this :P

    wait it's not workinng
    Re-uploaded them
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    hay guys im probably missing something simple here but how do you know what the oxidation state of Cr is in Na2CrO4. Its question 2aii in the jun 12 paper http://www.ocr.org.uk/Images/131295-...-materials.pdf
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    (Original post by MTI)
    hay guys im probably missing something simple here but how do you know what the oxidation state of Cr is in Na2CrO4. Its question 2aii in the jun 12 paper http://www.ocr.org.uk/Images/131295-...-materials.pdf
    oxygen is always -2
    Na is group 1 so +1

    totalling them up gives +2 -8 = -6
    So for the whole molecule to be neutral the Cr must have +6 state
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    (Original post by MTI)
    hay guys im probably missing something simple here but how do you know what the oxidation state of Cr is in Na2CrO4. Its question 2aii in the jun 12 paper http://www.ocr.org.uk/Images/131295-...-materials.pdf
    You should know what Na is +1 while Oxygen is always -2, so Cr has an oxidation state of +6


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    (Original post by Tikara)
    oxygen is always -2
    Na is group 1 so +1

    totalling them up gives +2 -8 = -6
    So for the whole molecule to be neutral the Cr must have +6 state
    (Original post by super121)
    You should know what Na is +1 while Oxygen is always -2, so Cr has an oxidation state of +6
    haha thank you i feel silly now for not knowing Na is +1
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    (Original post by desiboy20395)
    Hi

    F334 JAN 2013 - Last question. how do you calculate rate of disappearance?!?!
    I was just about to ask this to, does anyone know?

    All i can assume is that to make iodine (I2) (i.e the rate of dissapearance of I-) is twice the rate given because you need 2I- to make I2. I have absolutely no idea if that is right but its all i can think of to justify getting the answer of 2.0 x 10-5. Hopefully someone else can confirm or correct me
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    http://www.ocr.org.uk/Images/79818-q...-materials.pdf

    question 1div, how does going over the end point make concentration of e300 seem lower? I don't understand this at all. (Or that rate of dissapearrance of i2 on that other paper. **** iodine)
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    (Original post by abzy1234)
    January Paper.pdf
    January MS.pdf

    Don't worry! It's only natural to get exam nerves now; best thing to do is go over you notes, finish off them past papers; so you can gain confidence for tomorrow. Try your best, and you'll get what you put in
    Thank you
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    Just did the Jan 13 paper and I got a worse mark than I did in January
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    Do Tm and Tg like go up with each other?
    What I mean is say Tm is 'higher than average' does that mean Tg is 'higher than average'?
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    what colours of compounds/ions etc do we need to have memorised for tomorrow? do we need to remember all the complex ion colours?
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    Whats the difference between a condensation reaction and an elimination reaction? I thought condensation was losing water but HCl can be lost too
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    Can someone explain the difference between secondary and tertiary structure for me? I know it's really simple but I never know how to write it... :/
 
 
 
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