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HELP 😭😭CHEMISTRY QUESTION ON pH change watch

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    HELPP!!! 😭😭😰
    In my revision guide its says "you need to add more weak base than strong base to a string acid to cuase a pH change , and the change is less pronounced. On the other hand, you need to add less strong base to a weak acid to see a large change in pH" .

    I dont get what the revision guidewas trying to say .

    I wouldd appreciate it so much if someone helped 😊😭
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    Assuming all acids and bases are monobasic, i.e. release 1 H+ or OH- per molecule.

    If you start with 1 mol HCl, the pH will be 0. Adding 0.5 mol of solid strong base or weak base will neutralise 0.5 mol of the acid and the pH will change to 0.3.

    "you need to add more weak base than strong base to a string acid to cuase a pH change , and the change is less pronounced" in this case is not correct.

    If you start with 0.5 mol of HCl and add 1 mol of strong or weak base, then there will be base left over. The strong base fully ionise and lead to a higher pH than the remainder of the weak base. In this case, the above statement is partially correct. The needing to add more is never correct.

    1 mol of a weak acid will require 1 mol of a weak or strong base to neutralise it, so "you need to add less strong base to a weak acid to see a large change in pH" is also wrong. Unless again, it is referring to making the pH change AFTER neutralisation. In which case, why even mention the initial weak acid?

    What revision guide is this? I'd throw it in the bin, if I were you.
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    (Original post by Pigster)
    Assuming all acids and bases are monobasic, i.e. release 1 H+ or OH- per molecule.

    If you start with 1 mol HCl, the pH will be 0. Adding 0.5 mol of solid strong base or weak base will neutralise 0.5 mol of the acid and the pH will change to 0.3.

    "you need to add more weak base than strong base to a string acid to cuase a pH change , and the change is less pronounced" in this case is not correct.

    If you start with 0.5 mol of HCl and add 1 mol of strong or weak base, then there will be base left over. The strong base fully ionise and lead to a higher pH than the remainder of the weak base. In this case, the above statement is partially correct. The needing to add more is never correct.

    1 mol of a weak acid will require 1 mol of a weak or strong base to neutralise it, so "you need to add less strong base to a weak acid to see a large change in pH" is also wrong. Unless again, it is referring to making the pH change AFTER neutralisation. In which case, why even mention the initial weak acid?

    What revision guide is this? I'd throw it in the bin, if I were you.

    thank youuuu !!!
 
 
 
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