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3 30 marks a solution containing acetic acid oxalic

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Unformatted text preview: otein behavior. 3. [30 marks] A solution containing acetic acid, oxalic acid, ammonia and pyridine has a pH of 9.00. All relevant equilibria are shown below. You do not know any formal concentrations of any of the species. (a) What fraction of ammonia is not protonated? (b) What is the principal species of oxalic acid in the solution (prove your answer)? Species Acetic acid, HAc Oxalic acid, H2Ox Equilibria Equilibrium constant Ammonia, NH3 Pyridine, R-N Regardless of how many equilibria are present, each individual equilibrium must be individually satisfied. Therefore, so that is . The fraction of unprotonated ammonia where the denominator comes from the mass balance for ammonia. Multiplying the right-hand side by 1, where yields where ratio is known. The fraction of unprotonated ammonia is0.363. A more pedestrian route: You could also rearrange to yield and then substitute into . (b) For the principal species of oxalic acid: . Since and . . Since Since , , and . , Ox2- is the principal species. 4.[70...
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