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AS Chemistry Rates of reaction

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    I'm doing a past paper question on rates of reaction. It talks about a reaction between hydrochloric acid and magnesium carbonate, and asks what would be the effect on the rate of reaction if the acid was changed. But says assume the concentration of both acids is the same. I have no idea what the answer is. I would have said about different concentrations of the acids but that's obviously not correct. Help!
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    (Original post by talliehughes)
    I'm doing a past paper question on rates of reaction. It talks about a reaction between hydrochloric acid and magnesium carbonate, and asks what would be the effect on the rate of reaction if the acid was changed. But says assume the concentration of both acids is the same. I have no idea what the answer is. I would have said about different concentrations of the acids but that's obviously not correct. Help!
    Does it say what acid it is changed to? It will more than likely be something to do with mole ratios.
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    (Original post by talliehughes)
    I'm doing a past paper question on rates of reaction. It talks about a reaction between hydrochloric acid and magnesium carbonate, and asks what would be the effect on the rate of reaction if the acid was changed. But says assume the concentration of both acids is the same. I have no idea what the answer is. I would have said about different concentrations of the acids but that's obviously not correct. Help!
    It doesn't matter what acid is used.

    As long as the concentration of both are the same then we will have an equal no. of hydrogen ions reacting in the mixture.

    Hence, the rate will not change.

    EDIT: I strongly suggest reading the two posts after this one.
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    (Original post by Ari Ben Canaan)
    It doesn't matter what acid is used.

    As long as the concentration of both are the same then we will have an equal no. of hydrogen ions reacting in the mixture.

    Hence, the rate will not change.
    What about a strong diprotic acid, e.g. H2SO4?
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    (Original post by thegodofgod)
    What about a strong diprotic acid, e.g. H2SO4?
    The concentration is assumed to be the same.

    EDIT : I see where you are coming from.... I was thinking in terms of the concentration of H+ ions being the same. A diprotic acid of equal concentration as HCl would produce twice as many hydrogen ions and hence there would be double the no. of H+ ions.
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    All it says is "replace with weak acid" that's why I would have mentioned about the concentration but then it says "assume the concentration of both acids and all other conditions are the same." I would have mentioned that the rate wouldn't change also but it asks us to sketch a curve on the graph next to the previous reaction with the hydrochloric acid. So I wasn't sure.
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    (Original post by talliehughes)
    All it says is "replace with weak acid" that's why I would have mentioned about the concentration but then it says "assume the concentration of both acids and all other conditions are the same." I would have mentioned that the rate wouldn't change also but it asks us to sketch a curve on the graph next to the previous reaction with the hydrochloric acid. So I wasn't sure.
    If it's a weak acid then it doesn't undergo ionisation easily. Hence, there is likely to be a low concentration of H+ ions in the reaction mixture.

    Thus, the reaction rate falls.

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