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    (Original post by cuckoo99)
    i put initial : colourless
    final observation : no observable change
    Cool well thats one mark gone then i put black to colourless
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    (Original post by loknath)
    Ive lost about 25 marks so a B/C ****tttttt
    Bye bye university
    Actually, an A has never been higher than 74/100, and is usually 72/100 , so 25 lost marks will get you 75/100 which is an A...

    I need 80 ums out of 120 (66%ums) for an A overall in chem.. and i lost about 30 marks. I'm going to be borderline A/B it seems.. hopefully on the side of the A borderline.. otherwise no dentistry ..
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    (Original post by PhoenixSeeker)
    Cool well thats one mark gone then i put black to colourless
    which is black ? dont remember any complexes being black
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    Can anyone remember the 3rd question for question 8
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    Probably the most obvious question on the paper, but what was the reason for not having kcl as the salt bridge?
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    (Original post by PhoenixSeeker)
    Did you put colourless going to colourless?
    That's what i put.

    Couple things about the last question though, i calculated the ratio to be Cobalt:Chloride 3:1, this is also the ratio i would have expected, as the cobalt complex was oxidised to 3+, and it said it was a solid (precipitate) it would be a neutral complex, so 3 chloride, i assume i messed up on the ratio.

    My catalyst reactions involved the Co3+ ion reacting with the reactant and water to from the product and hdrogen ions, then Co2+ reacting with Oxygen and hydrogen ions to form Co3+ and water, i assume its right because the water, hydrogen ions, and cobalt all cancelled out (if you multipled one of the reactions by 2) to give the original equation.

    The q=mc delta T question (doing Physics, im really glad that came up, aswell as E=hf (or v, whatever)), I calculated the moles of KBr, times that by the enthalpy of solution to give a value for q (in joules), then used the rearranged equation to find the temperature change.

    The blue/red light one, i assumed that for the complex to look red, it must absorb blue light (or the other way around, i cant quite remember) since the question stated Blue light frequency > red light frequency, and E=hf, then absorbing photons of a greater f would mean there was a higher energy change.

    Also, my enthalpy of lattice dissociation on Q1 was about 900 iirc.

    (Original post by toddyvedda)
    Probably the most obvious question on the paper, but what was the reason for not having kcl as the salt bridge?
    I took a stab in the dark, and said it was because it was soluble.

    Whats the consensus on the "why did electrons move from right to left" question? I put something along the lines of the left side having a higher concentration, so more Cu would be reduced (or oxidized, again, i cant remember), resulting in that electrode being positive, electrons move from negative to positive, so electrons would move right to left
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    (Original post by TLi1295)
    I put equal to...but I really wasn't sure if they wanted to know about the tiny difference in values...because obviously there would be a small amount of polarisation but AgCl is supposed to be largely ionic isn't it? It's not like Al2O3? I don't know :/

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    me too!!!
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    (Original post by Fergy94)
    I wrote colourless..
    Yay. That's another mark I've lost :cry2:.
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    (Original post by Tullia)
    The 'v' in the equation is the frequency of the light absorbed. This being blue light, as the solution was red, and the complementary colour to that transmitted is absorbed.

    As v is higher for blue light, and v is proportional to ΔE, then it was an increase.
    :lol: The chemistry Goddess has arrived. How did you find it?
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    (Original post by bananarama2)
    :lol: The chemistry Goddess has arrived. How did you find it?
    I'm pretty sure it's a guy.
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    right ok... question 6 now - please can somebody try and remember the question for 8c

    a) calculate the frequency of visible light absorbed and state the units (2)
    b) Why does this compound appear blue (2)
    c) Red/blue complex. Which has the largest value for deltaE (2)
    d) State 3 factors that affect the frequency of visible light absorbed (3)
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    (Original post by bananarama2)
    :lol: The chemistry Goddess has arrived. How did you find it?
    pretty sure Tullia is a dude.
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    For the colour change questions , i pput the right colour changes but for my equations i put things like Co3 2- and OH- in the equation , will i drop marks on this !? :s
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    (Original post by Pinkhead)
    pretty sure Tullia is a dude.

    (Original post by Padouken)
    I'm pretty sure it's a guy.
    Spoiler:
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    (Original post by mulac1)
    Can anyone remember the 3rd question for question 8
    Think you had to draw the structure of the Co complex with the di-amine molecule?
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    (Original post by bananarama2)
    :lol: The chemistry Goddess has arrived. How did you find it?
    Except he's not a girl :lolz:
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    Q5:

    a) why can KCl not be used as a salt bridge (1)
    b) why do the electrons flow from right to left (2)
    c) Why does the current fall to zero after some time (1)
    d) calculate the emf (1)
    e) Write the equation for the cell when it is being recharged (2)
    f) Give one reason why this cell produces CO2 (1)
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    (Original post by iLayton)
    Think you had to draw the structure of the Co complex with the di-amine molecule?
    brilliant thank you that was 3 marks.
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    (Original post by Dirtybit)
    Except he's not a girl :lolz:
    I know. It was an attempt at a joke :getmecoat:
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    (Original post by cuckoo99)
    in CGP book it has a graph which indicates that MgO has a higher melting point that Al2O3 and Na2O the reason for being higher than Na2O is because it forms 2+ ions so bonds more strongly than 1+ ions in Na2O. But the melting point for AlO3 is lower than MgO despite the 3+ charge on the Al, it is lower because the bonds it forms are partialy covalent.

    It also states that Na2O MgO and Al2O3 all form giant ionic lattices.
    Covalent bonding always increase bond stability.
    Consider H2 this molecule has the strongest single bond of any non polar covalent bond. The molecule is symmetrical so absolutely no ionic bonds. The stability comes from the formation of molecular orbitals which in laymans terms give the electrons more places to go and so as a result there is some place where the elctrons are most stable known as the principal bonding orbital. In the case of H2 this the region between the two protons where an electron can interact with both nuclei and keep the two together.

    hence the correct answer is that the ionic models 's prediction for AgCl was too low as it did not include covalent character.

    The reason Al2O3 seems anomolous compared to MgO is nothing to do with bond polarity. It has a lower melting point because of the different crystal structure. The ratio of aluminium to oxygen is 2:3 which is quite awkward compared to 1:1. Hence Al2O3 packs less well (compactly) than MgO so even though Al2O3 has more covalent character than MgO it has a lower melting poit as the ionic proportion of its bonding- which is the majority even for Al2O3 is considerably lower than that of MgO.


    Did anybody else put the answer of the last question as [Co(NH3)6]Cl3 ?


    REASONING
    I believe this to be correct as The NH3 would displace H2O ligands forming the straw/pale yellow solution which would oxidise to the 3+ ion and then the Cl- ions would form the negative charge to form a neutral complex. The chloride ions aren't ligands! But the ratio was smaller 2.9 instead of 3 to 1 as some of the chloride ions had in fact become ligands so did not react with AgNO3
 
 
 
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