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Please explain this multiple choice answer, AS chemistry watch

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    I'm in year 12 and just got back my chemistry mock, and I messed up on some of the multiple choice answers. Would someone please explain why C is the correct answer to this question?

    'The percentage of iron in a sample of impure iron sulphate crystals can be determined by titrating solutions, made from separate weighed samples acidified with dilute sulphuric acid, against a standard solution of potassium manganate. Which of the following would lead to an inaccurate result? A(transferring the weighed sample of iron sulphate into a wet conical flask), B(failing to measure accurately the volume of water used to dissolve each weighed sample of iron sulphate), C(transferring the standard solution of potassium manganate from its original container to the burette using a wet beaker), or D(failing to measure accurately the volume of dilute sulphuric acid added to the mixture before titration).

    Apparently the correct answer is C, so could someone explain why C is the correct answer and not B or D?

    Thanks in advance.
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    is it because in C you are adding water to the potassium manganate so are diluting it so the concentration you think it is is now off slightly?
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    If you add extra liquid to standard solution and it goes above the measuring line (at 250ml) its considered diluted and so it would give innacurate results. so its c. if this happens in your practical you would have to make the standard solution over again
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    (Original post by shohaib712)
    If you add extra liquid to standard solution and it goes above the measuring line (at 250ml) its considered diluted and so it would give innacurate results. so its c. if this happens in your practical you would have to make the standard solution over again
    Okay, this makes sense... but can someone please explain why it isn't any of the other options?
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    (Original post by purpleunicorns)
    Okay, this makes sense... but can someone please explain why it isn't any of the other options?
    A) Its really hard to understand what this one means. Are they saying that they would titrate the Standard solution against the iron sulphate. So have the acidified solution in a flask and the alkali in the burette? If so it wouldnt change the result except you would find out the endpoint for the volume of alkali used.

    Or is it saying that you added it into a flask which could have impurities/water. if so i dont think it would react with it/affect the concentration of the solution. Were only interested in the concentration it doesnt matter if we added other things that would change the mass.

    This one is really confusing id suggest asking your teacher about this one.

    B) Doesnt matter how much we add its not gonna change the amout of the solute (iron). Its only going to change the concentration but were gonna titrate it so we would find out how concentrated it is anyways.

    d) Doesnt matter cuz the although it would change the endpoint, the amount of iron is still going to be the same. so if we did use too much acid the end point would be sooner *less acid would be needed to neutralise the alkali* but the amount of iron would still be the same and we would still get the same mass of iron once we did the mole equations.

    Hope this helps. Where did you get the questions from? Do you mind sending me a copy of the paper i think it would provide some good practice for my Alevel exams
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    (Original post by shohaib712)
    A) Its really hard to understand what this one means. Are they saying that they would titrate the Standard solution against the iron sulphate. So have the acidified solution in a flask and the alkali in the burette? If so it wouldnt change the result except you would find out the endpoint for the volume of alkali used.

    Or is it saying that you added it into a flask which could have impurities/water. if so i dont think it would react with it/affect the concentration of the solution. Were only interested in the concentration it doesnt matter if we added other things that would change the mass.

    This one is really confusing id suggest asking your teacher about this one.

    B) Doesnt matter how much we add its not gonna change the amout of the solute (iron). Its only going to change the concentration but were gonna titrate it so we would find out how concentrated it is anyways.

    d) Doesnt matter cuz the although it would change the endpoint, the amount of iron is still going to be the same. so if we did use too much acid the end point would be sooner *less acid would be needed to neutralise the alkali* but the amount of iron would still be the same and we would still get the same mass of iron once we did the mole equations.

    Hope this helps. Where did you get the questions from? Do you mind sending me a copy of the paper i think it would provide some good practice for my Alevel exams
    Sorry, I only have a physical copy of the paper, because it was from a mock exam we did in school! Thanks for the answer though.
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    (Original post by purpleunicorns)
    Sorry, I only have a physical copy of the paper, because it was from a mock exam we did in school! Thanks for the answer though.
    could you scan it/take a photogragh of it?
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    (Original post by shohaib712)
    could you scan it/take a photogragh of it?
    The whole paper?
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    (Original post by purpleunicorns)
    The whole paper?
    nevermind i have already found it online
 
 
 

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