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Author Topic: Calculationg percentage ionisation of a diprotic acid or base?  (Read 1744 times)

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lbjohnson

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Calculationg percentage ionisation of a diprotic acid or base?
« on: September 09, 2018, 10:15:14 PM »

Trying to calculate percentage ionisation of a compound at pH 7.4 with two pKa values of 1.5 and 10.5.

I know that for calculating percent ionised for a compound with one pKa value it's:

[tеx] Percent unionised = 100/1+10^pKa-pH [/tеx]

How do I calculate the % ionised for both pKa values simultaneously at pH 7.4?
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Borek

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Re: Calculationg percentage ionisation of a diprotic acid or base?
« Reply #1 on: September 09, 2018, 11:30:22 PM »

First of all: how do you define percentage of ionization for the multiprotic acid?

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lbjohnson

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Re: Calculationg percentage ionisation of a diprotic acid or base?
« Reply #2 on: September 25, 2018, 10:20:34 PM »

First of all: how do you define percentage of ionization for the multiprotic acid?

Do you mean this:

H2A ::equil::HA-+H+

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Borek

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Re: Calculationg percentage ionisation of a diprotic acid or base?
« Reply #3 on: September 26, 2018, 01:29:41 AM »

That's dissociation reaction, I asked how do you _define_ the value you want to calculate.

For a monoprotic acid HA of a total concentration CA percentage ionisation is rater trivial:

[tex]\% = \frac {[A^-]}{C_A} \times 100\%[/tex]

But how are you going to define it for H2A?
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