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    does anyone have the 2015 f324 and f325 papers please?
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    (Original post by ForgottenApple)
    There's also that one guy who posted the paper & answers on twitter right after the exam last year, crappy quality but I was able to check my answers reasonably well with it. (Think he made a mistake though so if you disagree on a question that'll be why...probably).
    Thank-you do you know what his name was? Haha ok thank-you hopefully it will just his mistake and not my own 😂
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    Does anyone know what factors affect the isoelectric point? I mean I know adding an NH2 group to the R group increases the pH but I don't understand why...?

    I think it's because if an amino acid has 2 'base' molecules than it is very likely to accept protons so it's very basic, which means a higher isoelectric point? Or in a higher pH the basic groups are more likely to want to accept protons? Idk


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    (Original post by Saywhatyoumean)
    Does anyone know what factors affect the isoelectric point? I mean I know adding an NH2 group to the R group increases the pH but I don't understand why...?

    I think it's because if an amino acid has 2 'base' molecules than it is very likely to accept protons so it's very basic, which means a higher isoelectric point? Or in a higher pH the basic groups are more likely to want to accept protons? Idk


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    It says on the spec 'state that different R groups in alpha amino acids may result in different isoelectric points' so I'm pretty sure that we just need to know that it does affect it but we don't have to explain how in the exam or predict the isoelectric point based on looking at the R groups? But I guess it would be helpful to understand it, my teachers didn't mention it at all though and it's not in the textbook which is weird

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    (Original post by LThomas694)
    It says on the spec 'state that different R groups in alpha amino acids may result in different isoelectric points' so I'm pretty sure that we just need to know that it does affect it but we don't have to explain how in the exam or predict the isoelectric point based on looking at the R groups? But I guess it would be helpful to understand it, my teachers didn't mention it at all though and it's not in the textbook which is weird

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    The only thing you need to know other then that is if r is a cooh group or nh3 how that changes the isoelectric
    point it has come up before


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    (Original post by CSLady)
    The only thing you need to know other then that is if r is a cooh group or nh3 how that changes the isoelectric
    point it has come up before


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    Only this will come up, or at the most a very unsubtle question, with either a lot of amine or COOH groups with a very obviously basic/acid pH and asked to match them up.
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    (Original post by LThomas694)
    It says on the spec 'state that different R groups in alpha amino acids may result in different isoelectric points' so I'm pretty sure that we just need to know that it does affect it but we don't have to explain how in the exam or predict the isoelectric point based on looking at the R groups? But I guess it would be helpful to understand it, my teachers didn't mention it at all though and it's not in the textbook which is weird

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    (Original post by CSLady)
    The only thing you need to know other then that is if r is a cooh group or nh3 how that changes the isoelectric
    point it has come up before


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    (Original post by ForgottenApple)
    Only this will come up, or at the most a very unsubtle question, with either a lot of amine or COOH groups with a very obviously basic/acid pH and asked to match them up.
    Thanks for the response, I was just confused at how much we needed to know
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    (Original post by CSLady)
    The only thing you need to know other then that is if r is a cooh group or nh3 how that changes the isoelectric
    point it has come up before


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    (Original post by ForgottenApple)
    Only this will come up, or at the most a very unsubtle question, with either a lot of amine or COOH groups with a very obviously basic/acid pH and asked to match them up.
    Thank you! So does a basic R group increase the isoelectric point and an acidic R group decrease it?

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    (Original post by LThomas694)
    Thank you! So does a basic R group increase the isoelectric point and an acidic R group decrease it?

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    That's what I was taught^ (:
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    (Original post by ReeceM1)
    That's what I was taught^ (:
    Okay thank you! We weren't taught it and I can't find it in the revision guide or textbook so it's so weird

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    I know this is a chemistry thread but just wanted to ask did you do solomon papers to prepare for c4 and c3, and roughly wat marks were you getting with these papers?
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    How prepared is everyone?


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    (Original post by SSAA9)
    How prepared is everyone?


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    Considering that I forgot the formula for Photosynthesis, I'm not feeling that prepared.

    What about you?
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    (Original post by Firenze26)
    Considering that I forgot the formula for Photosynthesis, I'm not feeling that prepared.

    What about you?
    In chemistry??😳
    Lol neither am i, had a mock today and it was horrible😔


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    (Original post by SSAA9)
    How prepared is everyone?


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    Not as prepared as I'd like to be lol


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    Help please
    I really don't know understand the measuring of rates of reaction using tangents on a graph - it doesn't make sense to me in the book
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    (Original post by tcameron)
    Help please
    I really don't know understand the measuring of rates of reaction using tangents on a graph - it doesn't make sense to me in the book
    Gosh, I wish I could help but I didn't even know you measure rates of reactions using tangents on a graph.

    I've heard of using the gradient as it is basically the (indicator of reaction)/(time) but I've never heard of using a tangent. Maybe you treat it as a mixture of a line of best fit and a regression line (used with scatter diagrams) of the curve?


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    (Original post by tcameron)
    Help please
    I really don't know understand the measuring of rates of reaction using tangents on a graph - it doesn't make sense to me in the book
    It's the same as drawing a tangent to a curve in maths. So you mark a point on the curve where you want to measure the rate of reaction, so for example after 6 seconds on the x axis, and then you draw a tangent to the curve at that point. And then you measure the gradient of the tangent so measure the gradient at that point on the curve. The gradient is equal to the rate of reaction because the gradient is change in y/change in x, and in a conc/time graph, the gradient is the change in concentration of a reactant/product over time, so it's equal to the gradient. So basically drawing a tangent is just a way of calculating the gradient, and therefore the rate of reaction at a particular point

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    (Original post by LThomas694)
    It's the same as drawing a tangent to a curve in maths. So you mark a point on the curve where you want to measure the rate of reaction, so for example after 6 seconds on the x axis, and then you draw a tangent to the curve at that point. And then you measure the gradient of the tangent so measure the gradient at that point on the curve. The gradient is equal to the rate of reaction because the gradient is change in y/change in x, and in a conc/time graph, the gradient is the change in concentration of a reactant/product over time, so it's equal to the gradient. So basically drawing a tangent is just a way of calculating the gradient, and therefore the rate of reaction at a particular point

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    I don't understand when it says like measure the rate after t=0 or t=20 where am I meant to start my line
    Would I start my line at 0 seconds? but then it's just a straight line not touching anything at 0 seconds
    The steepness of my tangent isn't always the same so my answers are different
    In the book on the page measuring reaction rates they do one where t=3000 and I have no idea when to know where to start your line and how to make sure it only touches in one place
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    (Original post by tcameron)
    I don't understand when it says like measure the rate after t=0 or t=20 where am I meant to start my line
    Would I start my line at 0 seconds? but then it's just a straight line not touching anything at 0 seconds
    The steepness of my tangent isn't always the same so my answers are different
    In the book on the page measuring reaction rates they do one where t=3000 and I have no idea when to know where to start your line and how to make sure it only touches in one place
    The method is the same for whatever value of t including t=0.
    You first mark the point on the curve where t=0 by drawing an x or a dot.
    You then draw a straight line that touches the curve where you've drawn the dot, and you make sure that the gradient of the line is same as the gradient at that point which is kinda hard to get accurate but usually in exam papers they will have drawn the curve our for you and they allow you a range of answers because it's hard to get it exactly right.
    It's hard to explain without drawing it out for you so it might help to get someone in your class or a teacher to draw one and show you how they do it?
    And then you measure the gradient of the tangent which is alright because the tangent is just a straight line.
    For t=0 it's just the same as any other value of t. You draw an x or a dot at t=0 and you then draw a tangent that's touching where you've drawn the dot. You're basically measuring the gradient of the very first bit of the curve where the gradient is steepest.
    It doesnt matter if it touches in more than one place you just draw a tangent touching the curve at t=3000 and measure the gradient of the tangent.
    When drawing the line you just line up your ruler so it's touching the dot and has the same gradient as the curve and you just draw a straight line that can be as long or as short as you like it doesn't matter where the line starts or ends?

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