confused2021 Posted February 17, 2021 Share Posted February 17, 2021 Hello. My question is as follows :Calculate the pI of Leucine pKa (carboxyl) = 2.4; pKa (amino) = 9.6; What is the ratio of COO- : COOH at pH 3.4? For pI I get 6 (9.6 + 2.4/2 = 6). I am having great difficulty with the 2nd part of the question. I get 63.8% COO-: 36.2% COOH. I deduced this since 50% is dissociated at pH2.4 and 100% is dissociated at pH6. There are 3.6 units from 2.4 to 6. Since it is one above 2.4, I divided 1/3.4 and multiplied it by 50 to get 13.8%. This added to the 50% dissociated at 2.4pH equals 63.8% dissociated and 36.2% not dissociated. Any help on how to reason this out to get the right answer would be greatly appreciated!!!! Link to comment Share on other sites More sharing options...
BabcockHall Posted April 14, 2021 Share Posted April 14, 2021 Did you try using the Henderson-Hasselbalch equation? Link to comment Share on other sites More sharing options...
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