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    Hi! I was doing some revision (via practice questions) and I got this answer wrong but I don't understand why the answer is what it is and so I was wondering whether any of you could help?

    The question says

    Which of the following statements are correct about a solution of weak acid?

    1) It contains only HA, H+ and A- ions

    2) It has a pH between 3 and 7

    3) It will neutralise less sodium hydroxide than the same volume of a strong acid of the same concentration.

    They say that only statement 1 is correct but I thought statement 3 would be as well because weak acids don't fully dissociate.

    When I looked at the answer their reasoning for why statement 3 wasn't correct was "weak acids ionise completely in their reactions with alkalis".

    I'm very confused. Any help would be greatly appreciated.

    Thanks,
    Blake
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    (Original post by Blake Jones)
    Hi! I was doing some revision (via practice questions) and I got this answer wrong but I don't understand why the answer is what it is and so I was wondering whether any of you could help?

    The question says

    Which of the following statements are correct about a solution of weak acid?

    1) It contains only HA, H+ and A- ions

    2) It has a pH between 3 and 7

    3) It will neutralise less sodium hydroxide than the same volume of a strong acid of the same concentration.

    They say that only statement 1 is correct but I thought statement 3 would be as well because weak acids don't fully dissociate.

    When I looked at the answer their reasoning for why statement 3 wasn't correct was "weak acids ionise completely in their reactions with alkalis".

    I'm very confused. Any help would be greatly appreciated.

    Thanks,
    Blake
    weak acids partially dissociate in aqueous solution, correct.

    As you add alkali, it takes up the dissociated protons, by Le Chatelier's principle this causes more of the acid to dissociate so more protons are available and so on. Eventually all the protons from the weak acid will be taken up by the added alkali, so a weak acid can neutralise the same amount of alkali as a strong acid!

    hope that makes sense, as always, just ask if anything needs clarifying
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    (Original post by MexicanKeith)
    weak acids partially dissociate in aqueous solution, correct.

    As you add alkali, it takes up the dissociated protons, by Le Chatelier's principle this causes more of the acid to dissociate so more protons are available and so on. Eventually all the protons from the weak acid will be taken up by the added alkali, so a weak acid can neutralise the same amount of alkali as a strong acid!

    hope that makes sense, as always, just ask if anything needs clarifying
    Awesome! Thank you! That makes sense
 
 
 
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