Ignoring Second Deprotonation

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Joey_Okumura_1E
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Joined: Wed Sep 30, 2020 9:58 pm

Ignoring Second Deprotonation

Postby Joey_Okumura_1E » Sat Jan 16, 2021 11:21 pm

When calculating pH, how do you know when it is acceptable to ignore the second deprotonation for a polyprotic acid? Can you always assume it is negligible?
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Victor Qiu 1C
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Re: Ignoring Second Deprotonation

Postby Victor Qiu 1C » Sun Jan 17, 2021 8:53 am

Take H3PO4 as an example, Ka1=7.1 × 10-3, Ka2=6.3 × 10-8, Ka3=4.5 × 10-13. The difference between Ka1 and Ka2 is at the scale of 105. Thus, I think if it is not clarified specifically, the second deprotonation can often be ignored.
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David Jen 1J
Posts: 107
Joined: Wed Sep 30, 2020 9:33 pm

Re: Ignoring Second Deprotonation

Postby David Jen 1J » Thu Jan 28, 2021 7:26 pm

is there a specific cut off point for this though? Like a difference of 10^-3 or more?
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