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    (Original post by KB_97)
    ah. Okay. I kinda get it now. I didn't know enthalpy solution= hydration enthalpy - lattice enthalpy. But it makes sense using a born haber cycle.

    You get 3 marks for talking about lattice enthalpy and hydration enthalpy and how it's both more -ev for KF and the normal explanation thing we're used to. But last mark is for saying that lattice enthalpy has a larger effect than hydration enthalpy. Does anyone know why? Is it because it's just a larger negative number than hydration enthalpy?
    With lattice enthalpy the attraction is between two oppositely charged ions whereas in hydration the attraction is between one charged ion and a water molecules. having two oppositely charged ions will release more energy when they collide in comparison to one ion colliding with a water molecule. giving lattice enthalpy to be more negative as you said and hence having greater affect on the enthalpy change of solution as you said.
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    Could anyone help me with june 14 8A,8b and 8e
    Edit:Nvm think I got it
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    (Original post by maisym00)
    Does anyone know where you can get some difficult practice questions for this unit? I've done all the past papers and am trying to find some more questions to do
    Try AQA and Edexcel papers. There are LOADS of Edexcel papers since they do the IAL as well which has January and June papers. Some stuff is not relevant to us and they are hard though!
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    (Original post by vishva97)
    With lattice enthalpy the attraction is between two oppositely charged ions whereas in hydration the attraction is between one charged ion and a water molecules. having two oppositely charged ions will release more energy when they collide in comparison to one ion colliding with a water molecule. giving lattice enthalpy to be more negative as you said and hence having greater affect on the enthalpy change of solution as you said.
    Thank you!!
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    Hey can someone please explain 4e from the june 2011 paper please?? I
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    Remember that if an element or ion has changed states in a reaction (i.e aqueous to solid) it must be included in the ionic equation!!
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    (Original post by selenmer)
    Hey can someone please explain 4e from the june 2011 paper please?? I
    Does this help? I chose lactic acid because if pKa 3.86 gives a pH of 2.11 then the closest one to pH od 3.55 would be lactic..looking at the answer from 4 c). And then you just find the ratio
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    (Original post by milutin767)
    Does this help? I chose lactic acid because if pKa 3.86 gives a pH of 2.11 then the closest one to pH od 3.55 would be lactic..looking at the answer from 4 c). And then you just find the ratio
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    I think you choose lactic acid because buffer solutions work best if PH=PKa, so the closest pka was lactic acid, well thats how I went about it anyway
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    (Original post by milutin767)
    Does this help? I chose lactic acid because if pKa 3.86 gives a pH of 2.11 then the closest one to pH od 3.55 would be lactic..looking at the answer from 4 c). And then you just find the ratio
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    Hey! Thank you very much for your help! But I was wondering how you know that buffer solutions work well if pka is similar to ph?
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    (Original post by HFancy1997)
    I think you choose lactic acid because buffer solutions work best if PH=PKa, so the closest pka was lactic acid, well thats how I went about it anyway
    How do you know that it works well if ph=pka ?
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    (Original post by selenmer)
    How do you know that it works well if ph=pka ?
    Explained in this video:

    https://www.youtube.com/watch?v=tsS_T2Cph28
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    What does a very negative exothermic value mean? More energy is needed to make the bonds than something with a less negative exothermic value?
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    (Original post by uk_shahj)
    Explained in this video:

    https://www.youtube.com/watch?v=tsS_T2Cph28
    Thank you so much
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    (Original post by annaj97)
    What does a very negative exothermic value mean? More energy is needed to make the bonds than something with a less negative exothermic value?
    Yes think about bendomexo, if it has a very negative value, it is more exothermic, therefore the attraction between the ions or whatever is greater, and more energy is released when bonds are made between them
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    If the Ka of and Ch3Cooh is 1.25(random)
    why is the Ka of the buffer solution also 1.25? Should it not be different as the Ch3Coo- concentration is coming from the salt of the acid so the Ka of the buffer would be different as there are different ch3coo- concentrations.

    TLDR Same equation, different concentration so different Ka???
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    (Original post by AqsaMx)
    Attachment 552624

    Ca anyone explain how to calculate the gas C?
    I worked it out by writing the other products and seeing what was left over in the reactions giving me N2 but the ms shows a calculation, which I don't understand. Could anyone explain the calculation please?
    This is what I think, but not 100% sure on my answer for B

    It's N2 because basically the question was talking about 1.17gcm-3 but in words to make it more confusing
    You need to x24 to get the Mr of your gas as 28.08 which is N2
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    (Original post by HFancy1997)
    If the Ka of and Ch3Cooh is 1.25(random)
    why is the Ka of the buffer solution also 1.25? Should it not be different as the Ch3Coo- concentration is coming from the salt of the acid so the Ka of the buffer would be different as there are different ch3coo- concentrations.

    TLDR Same equation, different concentration so different Ka???
    Is this actual a question in a paper since you've said your concentration is randomly made up
    Otherwise I would think the ka would be different as well
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    can someone pls explain part ii)

    https://gyazo.com/ab8f36e27a338e17312ffcc9a86183d8
    https://gyazo.com/f90cb74c027aac2acd3cc8d3f2b33cf0 (question)
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    (Original post by tcameron)
    Is this actual a question in a paper since you've said your concentration is randomly made up
    Otherwise I would think the ka would be different as well
    June 14, 6d. The answer uses Ka of the acid as the Ka for the buffer solution
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    because of machemguy grade boundaries will be sky high lol
 
 
 
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