why when you titrate a strong acid with a strong base the pH is 7 at equivalence point?

and why when you titrate a weak acid with a strong base at equivalence point is above 7?

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  • 1 decade ago
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    Note: If you observe a pH curve for a strong acid and a strong base the vertical portion is usually around this value .

    The equivalence point is defined as the point where you have added exactly the amounts of each substance as determined by the stiocheometric equation.ie)the reacting ratio.If the ratio is 1:1 and the concentrations are the same,the same volume of each is used.Why?

    The [OH-]=[H+] and cancel each other out so there is neither an excess nor deficeit of each ion and this results in a neutral solution of pH 7.

    Weak acids dissociates incompletely producing only a fraction of the H+ ions present.In this case [OH-]>[H+],the resulting solution has more OH- ions and is alkaline(pH greater than 7).

    Good Luck!

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