Titrations and Equivalence Points

TripleDegree

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Another question - as test day approaches and my BP inches upwards.... (time to stimulate my ADHRH)

Anyway - is there an intuitive way of understanding equivalence and half-equivalence points? I understand the technical definition, but find it really hard to solve problems since I guess I don't really understand the concept. And when it comes to diprotic acids, I am often clueless.

Any tidbits would be welcomed
 

indo

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TripleDegree said:
Another question - as test day approaches and my BP inches upwards.... (time to stimulate my ADHRH)

Anyway - is there an intuitive way of understanding equivalence and half-equivalence points? I understand the technical definition, but find it really hard to solve problems since I guess I don't really understand the concept. And when it comes to diprotic acids, I am often clueless.

Any tidbits would be welcomed


Think about the equiv. and 1/2 equiv. points in terms of what species of the biprotic acid are left.

1. H2A + H2O -> HA- + H3O
At the 1/2 point [H2A]=[HA-]
At the 1st eq point the solution is all HA- and you can use the pKa2 to find the pH but don't forget the change in volume when doing the calculations.

2. HA- + H2O -> A2- + H3O
Same thing applies here but us the pKb to find the pH at the endpoint.
 
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