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OCR Chemistry A Exam Thread (Breadth - May 27 2016 and Depth - June 10 2016) Watch

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    What points did you write for the bond angle question and the explanation: I was suprised that it was 4 marks. This is what i wrote:
    1) 104.5
    2) Electron pairs repel as far as possible.
    3) Lone pairs repel more than bonded pairs decreasing bond angle by 2.5 per lone pair?
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    (Original post by Ajan123)
    What points did you write for the bond angle question and the explanation: I was suprised that it was 4 marks. This is what i wrote:
    1) 104.5
    2) Electron pairs repel as far as possible.
    3) Lone pairs repel more than bonded pairs decreasing bond angle by 2.5 per lone pair?
    yeah that's exactly what I put 😊
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    (Original post by Ajan123)
    What points did you write for the bond angle question and the explanation: I was suprised that it was 4 marks. This is what i wrote:
    1) 104.5
    2) Electron pairs repel as far as possible.
    3) Lone pairs repel more than bonded pairs decreasing bond angle by 2.5 per lone pair?
    I just mentioned this and just said 'Lone pairs repel each other with greater force, hence squashing the bonded pairs slightly together' but I think you'd get a mark for stating "two lone pairs and to bonded pairs around central atom"
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    (Original post by Ajan123)
    What points did you write for the bond angle question and the explanation: I was suprised that it was 4 marks. This is what i wrote:
    1) 104.5
    2) Electron pairs repel as far as possible.
    3) Lone pairs repel more than bonded pairs decreasing bond angle by 2.5 per lone pair?
    In a rush i messed that up and only realised at the end - would i get one mark for mentioning about the bonded pairs repel each other and spread out as far as possible even though i got the angle wrong?
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    Butanoic acid is 100% wrong, sorry It told you in the question the 2nd largest peek belonged to a secondary carbocation at the bottom. Therefore, it HAS to be a branched structure.
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    (Original post by ComputeiT)
    In a rush i messed that up and only realised at the end - would i get one mark for mentioning about the bonded pairs repel each other and spread out as far as possible even though i got the angle wrong?
    I really don't think the angle was 104.5, the bond was c-O-h right, O central atom
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    (Original post by HarrisonGCSE)
    Butanoic acid is 100% wrong, sorry It told you in the question the 2nd largest peek belonged to a secondary carbocation at the bottom. Therefore, it HAS to be a branched structure.
    Was it second largest? I thought it said the peak in the most abundance 🤔🤔
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    (Original post by HarrisonGCSE)
    Butanoic acid is 100% wrong, sorry It told you in the question the 2nd largest peek belonged to a secondary carbocation at the bottom. Therefore, it HAS to be a branched structure.
    true
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    (Original post by ineedA)
    I really don't think the angle was 104.5, the bond was c-O-h right, O central atom
    Two lone pairs, two bonded pairs; 104.5 and non-linear
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    (Original post by alevelnerd123)
    1, if that. If a lot of people but butanoic acid they might accept it... because it's not wrong as such, it's just a different isomer. I did the same as you
    It is wrong though because they said the biggest peak was a secondary carbocation which was at 43 which fits with 2-methylpropanoic acid because of the CH3CHCH3 but not in butanoic acid.

    I can't believe that I figured it out almost right after the exam finishes. I swear this happens all the time. I'm sitting there thinking of the questions and I realise I made a mistake. Oh well, it's not that many marks. I think I did well in the rest.
    (Original post by katiekat0208)
    My teacher said that you'd only lose like 1 mark for that 2 marks at the most. I think
    Thanks

    (Original post by Major Wilson)
    Given that you have used the evidence appropriately you should lose just one.
    Thanks
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    (Original post by HarrisonGCSE)
    Butanoic acid is 100% wrong, sorry It told you in the question the 2nd largest peek belonged to a secondary carbocation at the bottom. Therefore, it HAS to be a branched structure.
    How many marks will I lose if I did everything else right?
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    (Original post by TH3-FL45H)
    It is wrong though because they said the biggest peak was a secondary carbocation which was at 43 which fits with 2-methylpropanoic acid because of the CH3CHCH3 but not in butanoic acid.



    Thanks
    What about [CH3CH2CH2]?
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    (Original post by ineedA)
    I don't think there are lone pairs
    An oxygen atom has six electrons in its outer shell, two of which were bonded. Leaving four which is two lone pairs.
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    I really failed to see how the C-O-H bond was 104.5, cause I worked it out and got 109.5, but the question said non-linear so I just went with 104.5?? Anyone else have this problem?
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    (Original post by KevinClyde)
    What about [CH3CH2CH2]?
    Thats not a secondary carbocation. The carbocation is the last carbon (as its only bonded to 3 atoms) in that which means it's primary.

    In CH3CH(CH3)COOH you get a secondary carbocation as you get CH3CHCH3 where the second carbon is only attached to 3 atoms so thats a secondary carbocation

    I don't think we'll lose that many marks tbh. I thought 2 but people are saying 1 so I'm hopeful.
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    (Original post by ineedA)
    I don't think you can assume this
    What do you mean you can't assume that oxygen has two lone pairs? It DOES. You were also told in the question that it was non-linear, so it was 104.5 anyways
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    (Original post by alevelnerd123)
    I really failed to see how the C-O-H bond was 104.5, cause I worked it out and got 109.5, but the question said non-linear so I just went with 104.5?? Anyone else have this problem?
    109.5 because four pairs of electrons make it tetrahedral and then two lone pairs take off 2.5 degrees each so it becomes 104.5
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    (Original post by KevinClyde)
    What about [CH3CH2CH2]?
    Thats a primary carbocation, not secondary
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    (Original post by KevinClyde)
    What do you mean you can't assume that oxygen has two lone pairs? It DOES. You were also told in the question that it was non-linear, so it was 104.5 anyways
    Probably trolling
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    (Original post by KevinClyde)
    An oxygen atom has six electrons in its outer shell, two of which were bonded. Leaving four which is two lone pairs.
    Didn't realise the question said non linear , oops how many makrs was that
 
 
 
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