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

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    (Original post by TeachChemistry)
    No
    Initial rate of reaction decreases in first 200 seconds since less particles per unit volume hence frequency of effective collisions decreases?
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    (Original post by ronnydandam)
    Initial rate of reaction decreases in first 200 seconds since less particles per unit volume hence frequency of effective collisions decreases?
    Surely there is only one 'initial rate of reaction' and it has one value.
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    (Original post by TeachChemistry)
    Surely there is only one 'initial rate of reaction' and it has one value.
    Yeah I mean rate. For that 2 marker about why it decreases in first 200 secs
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    (Original post by ronnydandam)
    Yeah I mean rate. For that 2 marker about why it decreases in first 200 secs
    Then you are likely to get the marks.
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    (Original post by TeachChemistry)
    Then you are likely to get the marks.
    Cheers, sorry for all the questions
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    (Original post by ronnydandam)
    Cheers, sorry for all the questions
    No problem. As it's a forum it's up to me whether I answer anyway.
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    Could someone tell me if what i have done is right and the amount of marks i would get:

    1) For the first 6 marker i talked about electrophillic addition fully drew a diagram and referred to carbocation stability (alkyl groups) and said how this could lead to a more likely product to be formed.

    2) Not sure if this is right but drew a line across the point it asked and worked out gradient by subtracting the y value by 0 and dividing it by the x value minus 0.
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    (Original post by hashman)
    when you name the molecule doesnt the bromo come before the methyl and when there are 2 methyls isnt it dimethyl because i got something like that
    Technically yes, because it goes in alphabetical order, but I knew what he meant


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    (Original post by TeachChemistry)
    Please feel free to stalk my previous posts and prove yourself incorrect. Goodbye.
    That's not proof. Students have been saying the same thing. And why would a teacher be on a thread like this anyways? Have you not got anything else to do?
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    (Original post by TeachChemistry)
    Happy?
    No, I'd like to see the question, then I'd be happy
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    (Original post by TeachChemistry)
    Yawn. Get back to me on 18th August.
    Why should I get back to you? What's my grade to you? And how does that answer what the question asked?
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    (Original post by 4nonymous)
    Why should I get back to you? What's my grade to you? And how does that answer what the question asked?
    He posted a pic of the paper. Call it a day


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    (Original post by MsDanderson)
    He posted a pic of the paper. Call it a day


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    But I would like to know what the question said. He comes in to the forum being rude to me for no reason so why should I call it a day. If I was wrong then so what. He didn't have to go off on one
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    (Original post by TeachChemistry)
    No problem. As it's a forum it's up to me whether I answer anyway.
    hey

    would we still get 2 out of 3 marks if we draw an incorrect tangent but use change in Y over change X to get the gradient for the rates question?

    And for the experiment question I wrote something like:
    place container and contents on mass balance and start timer and keep noting down mass after every 30 seconds and do it for 10 mins but make sure it is calibrated beforehand and then do 3 repeats and find mean average mass lost and then use that to find mean average rate of reaction? How many out of 3 marks do you think I have got? Thanks a lot!!
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    (Original post by TeachChemistry)
    No problem. As it's a forum it's up to me whether I answer anyway.
    also do you think the boundary will be less than 80% for an A since last year it was 46/60 and 78/100 which is 77.3% and it is new spec and with all content assessed in 1 exam so around 76%? Thank you
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    (Original post by alienz22)
    also do you think the boundary will be less than 80% for an A since last year it was 46/60 and 78/100 which is 77.3% and it is new spec and with all content assessed in 1 exam so around 76%? Thank you
    It is impossible to say. Don't waste time even thinking about this. I, and all of my students, thought the papers were both very fair.
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    (Original post by TeachChemistry)
    It is impossible to say. Don't waste time even thinking about this. I, and all of my students, thought the papers were both very fair.
    just worried that I may just miss out on an A if it's 80%... and I need an A* prediction but yes it is done now and I can't change it
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    (Original post by alienz22)
    hey

    would we still get 2 out of 3 marks if we draw an incorrect tangent but use change in Y over change X to get the gradient for the rates question?

    And for the experiment question I wrote something like:
    place container and contents on mass balance and start timer and keep noting down mass after every 30 seconds and do it for 10 mins but make sure it is calibrated beforehand and then do 3 repeats and find mean average mass lost and then use that to find mean average rate of reaction? How many out of 3 marks do you think I have got? Thanks a lot!!
    There will no doubt be a range for the tangent value. There will be a mark for showing it on the graph.

    The question required you to measure the volume of gas evolved. Does your method do this?
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    (Original post by alienz22)
    just worried that I may just miss out on an A if it's 80%... and I need an A* prediction but yes it is done now and I can't change it
    If my student was close to A boundary and I knew they had worked hard all year and thought they had the potential I may still predict A*.
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    (Original post by TeachChemistry)
    There will no doubt be a range for the tangent value. There will be a mark for showing it on the graph.

    The question required you to measure the volume of gas evolved. Does your method do this?
    ah that is relieving thank you., although most people did change in Y/200 where as I did change in y/176 cos my tangent, it wasn't 'for the first 200 secs' was it? and nope - only mass lost because because the graph just had seconds and mass - I am guessing I lost 2 marks there
 
 
 
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