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Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread watch

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    (Original post by Blazyy)
    Normally you'd get just Cr3+ by using the reactants I mentioned.There is no need to do anything, because Cr2+ and Cr3+ are in equilibrium, but the concentration of Cr2+ is very low because it immediately reacts with oxygen to make Cr3+. Although I'm not sure what to do if you want Cr3+ alone.
    Okay thank you for your help! 😊


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    (Original post by Wunderbarr)
    Would anyone kindly give a good but simple (Edexcel) definition of oxidation state/number ? The one with the bit about being an ion?
    Oh wait, I forgot to attach the question

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    (Original post by :D :))
    can someone explain to me why the answer to Q3 of JUNE 14R is D.
    Most negative electrode on the left hand side by convention so surely on the right it should be a more positive value las E RHS- E LHS.
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    (Original post by C0balt)
    RHS-LHS=emf
    yeah but can you explain it in terms of oxidation reduction. Because if the cells were the other way round that method wouldn't work
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    (Original post by Z.e.e)
    Al(OH)4-

    Mathematically speaking, try this

    x + (-4) = -1 where x is the oxidation state of Al and -4 is the oxidation state of OH

    x is 3
    Thank you, and Don Pedro too
    I knew Edexcel fried my brain with c3 already haha
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    (Original post by sayshay)
    Oh wait, I forgot to attach the question

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    Ok thanks!

    Although it spawns the question of whether "bonding electrons" would be suitable since transition elements have multiple oxidation states.
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    (Original post by sayshay)
    Oh wait, I forgot to attach the question

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    Which paper is this?
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    Can anyone help ?
    what I did was worked the out number of of moles of Cr2+ in the 250 cm^3 by dividing the 2.66 x 10^-3 by 10. I then used the equation involving the oxidation of Cr2+ to Cr3+ by Mno4 - to find the number of moles of Mno4 that will react with the cr2+ to changed it to cr3+ . so I got 5.32 x10 ^-5 for the moles of Mno4 thats needed to change cr2+ to cr3+, then I thought that changing Cr2+ to cr3+ involve increase in 1 oxidation state so in changing cr2+ to cr+6 I will need 4 times the moles of Mno4 but the answer I got using this method is only worth 3 marks ? Name:  IMG_20160621_184421_edit.jpg
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    (Original post by Franckenstar)
    No because you need to keep it under hydrogen atmosphere as oxygen in the air will oxidize cr2+ to cr3+
    It's a nitrogen atmosphere (inert).
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    Guys how would you draw the displayed structure of nitrobenzene?
    It looks like the nitrogen forms 5 bonds (two with each oxygen and one with the benzene ring), but if that's the case, shouldn't it have a charge? :/




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    (Original post by Whizbox)
    Which paper is this?
    June 2013 R


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    anyone got a copy of jan 16 IAL paper + mark scheme + report? would be appreciated
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    Gonna get a few hours sleep.
    I'll revise after suhoor.

    Good luck everyone, may the odds be ever in your favour.
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    Someone explain why it's C please?

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    (Original post by sayshay)
    Guys how would you draw the displayed structure of nitrobenzene?
    It looks like the nitrogen forms 5 bonds (two with each oxygen and one with the benzene ring), but if that's the case, shouldn't it have a charge? :/




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    There are some few ways of drawing it from my travels.

    But generally I've seen the N having a positive charge and then single bond O with a negative charge.
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    (Original post by sayshay)
    Guys how would you draw the displayed structure of nitrobenzene?
    It looks like the nitrogen forms 5 bonds (two with each oxygen and one with the benzene ring), but if that's the case, shouldn't it have a charge? :/




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    Look it up on Google; the N has a + charge and the O has a - charge apparently!
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    https://a5c076379da85d2c0b501a60f1a4...0Chemistry.pdf

    Q19ai) HOW do we know that the water from combustion is being measured?! theres no experiment outlined? And why is it unreasonable to assume that water could react with A??
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    (Original post by genevievelaw)
    anyone got a copy of jan 16 IAL paper + mark scheme + report? would be appreciated

    https://56leomessiphotoshop.blogspot...materials.html


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    Do all amino acids exist as zwitter ions in pH 7? The MC in June 14 asked what alanine would look like in pH 7...unless we're meant to know that the isoelectric point of alanine is pH 7?
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    (Original post by RUNSran)
    Can anyone help ?
    what I did was worked the out number of of moles of Cr2+ in the 250 cm^3 by dividing the 2.66 x 10^-3 by 10. I then used the equation involving the oxidation of Cr2+ to Cr3+ by Mno4 - to find the number of moles of Mno4 that will react with the cr2+ to changed it to cr3+ . so I got 5.32 x10 ^-5 for the moles of Mno4 thats needed to change cr2+ to cr3+, then I thought that changing Cr2+ to cr3+ involve increase in 1 oxidation state so in changing cr2+ to cr+6 I will need 4 times the moles of Mno4 but the answer I got using this method is only worth 3 marks ? Name:  IMG_20160621_184421_edit.jpg
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    Chromium (II) Ethanoate has two Chromium atoms so the moles of MnO4- needed would be 4x2 = 8. You should then get a titre value double what you got
 
 
 
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