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

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    Ok so let me get this straight. pH has nothing to do with whether something is acidic or alkaline? So when you heat water , equilibrium shifts to the right , producing more H+ ions and causes pH to go down? yet its still neutral???
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    (Original post by CLGC98)
    Ok so let me get this straight. pH has nothing to do with whether something is acidic or alkaline? So when you heat water , equilibrium shifts to the right , producing more H+ ions and causes pH to go down? yet its still neutral???
    Well it doesn't have nothing to do with it, on the whole it is a pretty good indicator but yes. Imagine the acid as you, and your friends as the base. If someone gave me £1 to give to each friend with me, and there were 10 people, then I have £10 pounds. If they instead gave me £14, but there were now 14 people, even though I am richer because the number of friends has also increased by the same amount I can still only give each of my friends one pound each. It is a similar story here, although the pH has decreased, because the concentration of the base and the acid both change by the same amount even though the pH is lower (richer in the example) the water is still neutral.
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    (Original post by CLGC98)
    Ok so let me get this straight. pH has nothing to do with whether something is acidic or alkaline? So when you heat water , equilibrium shifts to the right , producing more H+ ions and causes pH to go down? yet its still neutral???
    Yeo as concentration of h+ and oh- stay the same in equilibrium


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    (Original post by samb1234)
    Well it doesn't have nothing to do with it, on the whole it is a pretty good indicator but yes. Imagine the acid as you, and your friends as the base. If someone gave me £1 to give to each friend with me, and there were 10 people, then I have £10 pounds. If they instead gave me £14, but there were now 14 people, even though I am richer because the number of friends has also increased by the same amount I can still only give each of my friends one pound each. It is a similar story here, although the pH has decreased, because the concentration of the base and the acid both change by the same amount even though the pH is lower (richer in the example) the water is still neutral.
    Ah I see! thanks!
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    Please can someone explain the bromine clock reaction? Thank you
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    Hey, I have two multiple choice questions, can someone please help me ?
    • I understand that the K1 = K22 but why the standard enthalpy change of reaction has halved as well in the second equation?
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    • I get that chlorine cannot have a peak in the mass spectrum but i don't seem to find a fragment for the 37 and 78
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    (Original post by TeaAndTextbooks)
    Please can someone explain the bromine clock reaction? Thank you
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    https://www.scribd.com/doc/31083024/Bromine-Clock
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    (Original post by PlayerBB)
    Hey, I have two multiple choice questions, can someone please help me ?
    • I understand that the K1 = K22 but why the standard enthalpy change of reaction has halved as well in the second equation?
    Name:  g.JPG
Views: 101
Size:  30.7 KB
    • I get that chlorine cannot have a peak in the mass spectrum but i don't seem to find a fragment for the 37 and 78
    I think 78 refers to the parent ion peak (the one that shows the RMM of the compound). A Chlorine atom does not have mass of 35.5, 35.5 is the average mass of the chlorine atom.

    "The normal mass of Cl is 35 and 37 with a ratio of 3:1 so the AVERAGE mass of chlorine is 35.5. So you either get a peak of 37 or 35 but not 35.5." That's what I found on the interwebs
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    (Original post by PlayerBB)
    Hey, I have two multiple choice questions, can someone please help me ?
    • I understand that the K1 = K22 but why the standard enthalpy change of reaction has halved as well in the second equation?
    Name:  g.JPG
Views: 101
Size:  30.7 KB
    • I get that chlorine cannot have a peak in the mass spectrum but i don't seem to find a fragment for the 37 and 78
    As to why the standard enthalpy halves, I think it's because you have half the number of moles of reactants and products, so if you were to create a Hess cycle and use all the different enthalpies to calculate the standard enthalpy change, the values you use would be halved also, giving an overall answer which is half of the one above
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    (Original post by Don Pedro K.)
    I think 78 refers to the parent ion peak (the one that shows the RMM of the compound). A Chlorine atom does not have mass of 35.5, 35.5 is the average mass of the chlorine atom.

    "The normal mass of Cl is 35 and 37 with a ratio of 3:1 so the AVERAGE mass of chlorine is 35.5. So you either get a peak of 37 or 35 but not 35.5." That's what I found on the interwebs
    Ahh, thank you so much, I totally forgot about 3:1 ratio for chlorine atom
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    (Original post by Don Pedro K.)
    As to why the standard enthalpy halves, I think it's because you have half the number of moles of reactants and products, so if you were to create a Hess cycle and use all the different enthalpies to calculate the standard enthalpy change, the values you use would be halved also, giving an overall answer which is half of the one above
    Ahh, it makes sense, thanks
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    Anyone tried the January 2016 IAL paper? It's super nice, haha.
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    (Original post by Ayman!)
    Anyone tried the January 2016 IAL paper? It's super nice, haha.
    Yeah I didn't like it very much haha
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    (Original post by samb1234)
    Yeah I didn't like it very much haha
    Uh oh lol hope ours isn't like that then!
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    (Original post by Don Pedro K.)
    Uh oh lol hope ours isn't like that then!
    I have a habit of doing stupid stuff especially in multiple choice (like for example in that paper in my head went well it's clearly not a,b,c so it is d, then when I came to mark it I had crossed C even though I knew the answer) so I prefer papers with lower UMS
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    (Original post by samb1234)
    I have a habit of doing stupid stuff especially in multiple choice (like for example in that paper in my head went well it's clearly not a,b,c so it is d, then when I came to mark it I had crossed C even though I knew the answer) so I prefer papers with lower UMS
    Was the paper hard?
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    (Original post by Don Pedro K.)
    Was the paper hard?
    Not really no. I dropped 11 marks total pretty much exclusively from stupid mistakes which is 106 ums because of how high the ums was
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    (Original post by samb1234)
    Not really no. I dropped 11 marks total pretty much exclusively from stupid mistakes which is 106 ums because of how high the ums was
    Ohhh okay haha! So the paper itself was easy, you just had a bit of a silly moment ?
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    (Original post by Don Pedro K.)
    Ohhh okay haha! So the paper itself was easy, you just had a bit of a silly moment ?
    Well I nearly always lose at least 3 on mc, and then I just did some stupid stuff on a calculation one I hadn't done one of since I made unit 4 notes like a month ago
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    Argh... My brain is filled with geography and biology revision. Nothing from chemistry is going in. Even though I got As in the mocks, at this rate, I'm not going to be able to get it in the real thing.

    REALLY worried about Unit 4 on Tues.
 
 
 
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