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Equilibria, Energetics and Elements (F325) - June 2011 Exam. watch

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    (Original post by smoozth)
    Can someone help me with Q9 of the practice questions on P225 I'm stuck
    okay so to get the moles of NaS2O3 used you do 0.02015x0.2 = 0.00403 (n=c x v)
    as you can see, the ratio of thiosulfate:iodine is 2:1, but the ratio in the first equation of iodine:Cu2+ is 1:2, so the moles you've just calculated are the moles in 25cm3
    times 0.00403 by 10, so you have the moles in 250cm3
    c = n/v so 0.0403/0.25 = 0.1612 mol dm3
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    Can anyone explain how you know if a complex ion is tetrahedral or square planar?
    e.g. (CuCl4)2- is tetrahedral
    but (NiCl4) 2- is square planar
    how would you know if its what as they both have a coordination number of 4?
    plus whats the bond angle or tetrahedral and square planar?
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    (Original post by wilsea05)
    okay so to get the moles of NaS2O3 used you do 0.02015x0.2 = 0.00403 (n=c x v)
    as you can see, the ratio of thiosulfate:iodine is 2:1, but the ratio in the first equation of iodine:Cu2+ is 1:2, so the moles you've just calculated are the moles in 25cm3
    times 0.00403 by 10, so you have the moles in 250cm3
    c = n/v so 0.0403/0.25 = 0.1612 mol dm3
    Thanks
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    (Original post by Schoolio93)
    Hi can someone exactly tell me what we need to know about neutralisation? Do we need to know how to calculate the enthalpy of dissociation?
    We need to be able to define the enthalpy change of neutralisation which is the enthalpy change which accompanies the addition of aqueous base to neutralise aqueous acid, to form 1 mole of water.
    We then need to be able to use the equation Q= mc^T (had to use ^ to represent triangle!) to work out enthalpy changes- which was also covered at AS.
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    (Original post by cws121)
    Can anyone explain how you know if a complex ion is tetrahedral or square planar?
    e.g. (CuCl4)2- is tetrahedral
    but (NiCl4) 2- is square planar
    how would you know if its what as they both have a coordination number of 4?
    plus whats the bond angle or tetrahedral and square planar?
    At A level I think that we are surposed to assume that apart from cis-platin (NiCl2(NH3)2) which is teh drug we need to know about is the complex ion has a co-ordination number of 4 it has a tetrahedral shape.

    Tetrahedral shape = 109.5
    Square planar= 90
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    start doing the last two modules of unit 2 on monday afternoon and
    expecting to get 90%...........what are the chances???
    I havent even looked at it since January...it's just the last two, the first one
    I know it inside out....awwwr it F215 on monday
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    Can someone help me with this :
    FeO4 2- + H+ -------> O2 + H20 + Fe 3+
    Q asks to balance this? I think they use oxidation numbers for this: the answer is :
    4FeO4 2- + 20H+ ------->3 O2 + 10H20 + 4Fe 3+

    How did they do this??? I could just balance it when looking at the nunber of oxygens, hydrogens etc but i get different answer, Can someone please please help me out...
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    (Original post by wilsea05)
    ..
    Sorry for the inverted image but here it is

    The questions are:

    1. State the energy for the first electron affinity of chlorine

    2. Calculate the enthalpy formation of MgCl2
    Attached Images
     
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    (Original post by hey-hey-hey)
    Can someone help me with this :
    FeO4 2- + H+ -------> O2 + H20 + Fe 3+
    Q asks to balance this? I think they use oxidation numbers for this: the answer is :
    4FeO4 2- + 20H+ ------->3 O2 + 10H20 + 4Fe 3+

    How did they do this??? I could just balance it when looking at the nunber of oxygens, hydrogens etc but i get different answer, Can someone please please help me out...
    I think that you not only have to balance the numbers, but also the charges.
    So looking at their answer the charge on either side of the equation = +12
    This wouldn't be the case if you balanced only using oxidation numbers.
    I hope this makes sense, let me know if i'm not being clear!
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    (Original post by sportycricketer)
    Sorry for the inverted image but here it is

    The questions are:

    1. State the energy for the first electron affinity of chlorine

    2. Calculate the enthalpy formation of MgCl2
    1) -698 (E)
    2) that pictures really blurry but add (2xE) and F together, then take away (2xD), C and B from it, to get A (enthalpy change of formation)
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    (Original post by cws121)
    Can anyone explain how you know if a complex ion is tetrahedral or square planar?
    e.g. (CuCl4)2- is tetrahedral
    but (NiCl4) 2- is square planar
    how would you know if its what as they both have a coordination number of 4?
    plus whats the bond angle or tetrahedral and square planar?
    (Original post by science rules! :))


    At A level I think that we are surposed to assume that apart from cis-platin (NiCl2(NH3)2) which is teh drug we need to know about is the complex ion has a co-ordination number of 4 it has a tetrahedral shape.

    Tetrahedral shape = 109.5
    Square planar= 90
    This is right, but also i've been looking at mark schemes, and if there is four co-ordinate bonds in a complex ion they give marks for either tetrahedral or square planar - regardless of which is right.
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    (Original post by wilsea05)
    1) -698 (E)
    2) that pictures really blurry but add (2xE) and F together, then take away (2xD), C and B from it, to get A (enthalpy change of formation)
    1) why dont you multiply by 2? cos 2 moles of Cl have electron affinity?

    2) Isn't G enthalpy change of formation? I know the diagram is blurr but can you see and let me know?

    The values are:

    A = 148
    B = 736
    C = 1450
    D = 244
    E = -698
    F = -2522
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    How come when a system increases in entropy, it becomes energetically more stable?
    I thought if entropy increased, T(DeltaS) would increase, and that means that (Delta)G<0 which means the reaction is spontanoeous?? Or am i just overcomplicating things
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    (Original post by sportycricketer)
    1) why dont you multiply by 2? cos 2 moles of Cl have electron affinity?

    2) Isn't G enthalpy change of formation? I know the diagram is blurr but can you see and let me know?

    The values are:

    A = 148
    B = 736
    C = 1450
    D = 244
    E = -698
    F = -2522
    sorry yeah, thats laid out differently to how im used to.
    -2522-2x698=-3918 +148+736+1450+2x244 =-1096 kJ mol -1
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    (Original post by wilsea05)
    sorry yeah, thats laid out differently to how im used to.
    -2522-2x698=-3918 +148+736+1450+2x244 =-1096 kJ mol -1
    Alright thanks mate, thats what I got as well Just wanted to verify if the answer in the book was wrong!
    Last qs, so you have to multiply 2 by -698 right to work out the electron affinity? because its 2 moles?
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    how would i do the following question? i've tried everything but keep getting the wrong answers:

    1. 25.00cm^3 of an aqueous solution of ethanedioic acid reacted exactly with 15.0cm^3 of 0.0200 mol dm^-3 Manganate (VII) ions. Calculate the concentration of the solution of ethanedioic acid.

    The equation involved is:

    2MnO4^- + 5(COOH)2 + 6H+ ---> 2Mn2+ + 8H2O + 10CO2
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    Has anhyone got exam cafe answers for this unittt ???

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    (Original post by Princess_perfect786)
    how would i do the following question? i've tried everything but keep getting the wrong answers:

    1. 25.00cm^3 of an aqueous solution of ethanedioic acid reacted exactly with 15.0cm^3 of 0.0200 mol dm^-3 Manganate (VII) ions. Calculate the concentration of the solution of ethanedioic acid.

    The equation involved is:

    2MnO4^- + 5(COOH)2 + 6H+ ---> 2Mn2+ + 8H2O + 10CO2
    0.02x0.015x2.5, then divide by 0.025 = 0.03mol dm3
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    (Original post by Jtking3000)
    RES12_chem_book_answers.pdf:
    Your file of 1.89 MB bytes exceeds the forum's limit of 976.6 KB for this filetype.

    blast
    CAn you send it to me via email pleasee ?? if i pm you my email
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    (Original post by wilsea05)
    0.02x0.015x2.5, then divide by 0.025 = 0.03mol dm3
    why do you have to do this part?
 
 
 
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