Polyprotic buffers (20 pts) Phosphoric acid is a triprotic acid. Below are its dissociation equilibria. H* H H* 0 0 0 ||

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Polyprotic Buffers 20 Pts Phosphoric Acid Is A Triprotic Acid Below Are Its Dissociation Equilibria H H H 0 0 0 1 (256.19 KiB) Viewed 47 times

Polyprotic buffers (20 pts) Phosphoric acid is a triprotic acid. Below are its dissociation equilibria. H* H H* 0 0 0 || HO POH◄ O H SAMPLE MIDTERM 1 QUESTIONS Acid 0 HO pk =2.2 P T 0 H -O +0 pk =7.2 -P O T O H pk =12.3 Dibasic -2 0 0 P O O M M Monobasic -1 a) Circle the species that are amphoteric salts (1) (b-1) You want to prepare 750 mL of 10 mM potassium phosphate PH 7.0 buffer starting with 0.020 M phosphoric acid (H3PO4) and 0.20 M potassium hydroxide (KOH). The steps for doing this are already broken down so that you can demonstrate expertise at each step. b) What is the pH of the 0.20 M KOH solution? SHOW WORK (2) Tribasic -3 c) What is the APPROXIMATE pH of the 0.020 M phosphoric acid solution? DO NOT TRY TO BE EXACT SHOW WORK (3) d) What volume of 0.020 M phosphoric acid would you need to start with? mL (1) e) What would happen to the pH of the phosphoric acid solution if it was diluted to twice its volume with pure water? increase decrease (BE CAREFUL!) (1) remain the same f) For this pH 7.0 buffer solution, the relevant acid species (HA) is and the corresponding conjugate base (A-) (1, no partial). is g) What is the ratio of the conjugate base to acid at pH 7.0? SHOW WORK FOR CREDIT (2) h) What are the concentrations of [HA] and [A-] in the final 10 mM buffer at pH 7.0? SHOW WORK FOR CREDIT (3 acid conjugate base i) What final concentration of KOH would need to be added to achieve pH 7.0? SHOW WORK AND BE CAREFUL (2) j) What volume of 0.20 N KOH would need to be added? SHOW WORK (1) k) What is the final concentration of K+ ions? (1) 1) If you started with 0.020 M monobasic potassium phosphate (KH₂PO4) instead of phosphoric acid, what volume of base would you have needed to add instead? (Hint: you do not need to do a complete calculation, you already have everything you need to calculate this directly in one step). (2)