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Lidstrom:Buffers: Difference between revisions
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** The form the phosphate takes will shift based on how many protons are available in solution. Thus it can be a source/sink for protons. Like all (good) buffers, if more H+ ions show up in solution, it can help absorb these and maintain the initial pH. Converseley, it can release H+ ions when they disappear from solution. | ** The form the phosphate takes will shift based on how many protons are available in solution. Thus it can be a source/sink for protons. Like all (good) buffers, if more H+ ions show up in solution, it can help absorb these and maintain the initial pH. Converseley, it can release H+ ions when they disappear from solution. | ||
** The details: | ** The details: | ||
***Aqueous phosphate exists in four forms. In strongly basic conditions, the phosphate ion (PO<sub>4</sub><sup>3−</sup>) predominates, whereas in weakly basic conditions, the hydrogen phosphate ion (HPO<sub>4</sub><sup>2−</sup>) is prevalent. In weakly acid conditions, the dihydrogen phosphate ion (H2PO<sub>4</sub><sup>−</sup>) is most common. In strongly acidic conditions, trihydrogen phosphate (H< | ***Aqueous phosphate exists in four forms. In strongly basic conditions, the phosphate ion (PO<sub>4</sub><sup>3−</sup>) predominates, whereas in weakly basic conditions, the hydrogen phosphate ion (HPO<sub>4</sub><sup>2−</sup>) is prevalent. In weakly acid conditions, the dihydrogen phosphate ion (H2PO<sub>4</sub><sup>−</sup>) is most common. In strongly acidic conditions, trihydrogen phosphate (H<sub>3</sub>PO<sub>4</sub>) is the main form. | ||
* You can make phosphate buffers several ways. The difference between them is how much salt and what type of salt is also present in solution. | * You can make phosphate buffers several ways. The difference between them is how much salt and what type of salt is also present in solution. | ||
** If you want a desired pH, you can use a ratio of hydrogen phosphate and dihydrogen phosphate salts to get the pH you desire. There are tables that correlate desired pH values and concentrations to volumes you should use. | ** If you want a desired pH, you can use a ratio of hydrogen phosphate and dihydrogen phosphate salts to get the pH you desire. There are tables that correlate desired pH values and concentrations to volumes you should use. | ||
