Lesson plan
Isoionic point
The isoionic point is the pH value at which a zwitterion molecule has an equal number of positive and negative charges and no adherent ionic species. It was first defined by S.P.L. Sørensen, Kaj Ulrik Linderstrøm-Lang and Ellen Lund in 1926 and is mainly a term used in protein sciences. It is different from the isoelectric point (pI) in that pI is the pH value at which the net charge of the molecule, including bound ions is zero. Whereas the isoionic point is at net charge zero in a deionized solution. Thus, the isoelectric and isoionic points are equal when the concentration of charged species is zero. For a diprotic acid, the hydrogen ion concentration can be found at the isoionic point using the following equation : [H^+]=\sqrt{{K_1 K_2 C + K_1 K_w} \over {K_1 + C}} * [H^+] = hydrogen ion concentration * K_1 = first acid dissociation constant * K_2 = second acid dissociation constant * K_w = dissociation constant for water * C = concentration of the acid Note that if K_1 K_2 C \gg K_1 K_w then K_1 K_2 C + K_1 K_w \approx K_1 K_2 C and if C \gg K_1 then K_1 + C \approx C .…
Article summary
The isoionic point is the pH value at which a zwitterion molecule has an equal number of positive and negative charges and no adherent ionic species. It was first defined by S.P.L. Sørensen, Kaj Ulrik Linderstrøm-Lang and Ellen Lund in 1926 and is mainly a term used in protein sciences. It is different from the isoelectric point (pI) in that pI is the pH value at which the net charge of the molecule, including bound ions is zero. Whereas the isoionic point is at net charge zero in a deionized solution. Thus, the isoelectric and isoionic points are equal when the concentration of charged species is zero. For a diprotic acid, the hydrogen ion concentration can be found at the isoionic point using the following equation : [H^+]=\sqrt{{K_1 K_2 C + K_1 K_w} \over {K_1 + C}} * [H^+] = hydrogen ion concentration * K_1 = first acid dissociation constant * K_2 = second acid dissociation constant * K_w = dissociation constant for water * C = concentration of the acid Note that if K_1 K_2 C \gg K_1 K_w then K_1 K_2 C + K_1 K_w \approx K_1 K_2 C and if C \gg K_1 then K_1 + C \approx C .…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.