Blood is a buffered solution with pH values ranging from7.35-7.45. The important components of blood that contribute to itsbuffering capacity are species derived from carbonic acid andphosphoric acid. This problem emphasizes the phosphoric acidcomponent.
(a) (3 pts) What are the three additional species in solutionthat can be derived from phosphoric acid using Brønsted-Lowryacid-base concepts? (I will refer to them as Species #1, #2, and #3in the next parts.)
(b) (3 pts) Write the three equilibria that relate phosphoricacid with each of these species listed in part (a). (You shouldwrite three chemical equilibria, using chemical symbols, that allresemble the following.) “Phosphoric Acid†+ ___________ “Species#†+ ___________ (The items in blanks are needed to properlybalance the equations.)
(c) (3 pts) For a pH value of 7.40, calculate the followingratios (you may use relevant Ka values that are tabulated for 25ï‚°Cin Appendix D of your textbook): [Species #1] [Species #2] [Species#3] ; ; [Phosphoric Acid] [Phosphoric Acid] [Phosphoric Acid]
(d) (2 pts) Which forms of phosphoric acid are the most abundantand the least abundant in water at a pH of 7.40?
(e) (10 pts) You work in a medical research lab with abiochemist who asks you to make a 1.00 L phosphate buffer stocksolution with pH = 7.35. The total phosphorus concentration is tobe 0.150 M. In the storeroom, there are the following reagents: (1)a 3.00 M phosphoric acid stock solution, (2) solid sodiumdihydrogen phosphate, (3) solid sodium monohydrogen phosphate, (4)solid, sodium phosphate, (5) a 3.00 M HCl(aq) stock solution, (6) a3.00 M NaOH(aq) stock solution, and (7) deionized water.
(i) (2 pts) To make an optimum buffer, it is important that thepKa of the acid part is close to the target pH of the buffer. Whichphosphate species has a pKa value closest to pH = 7.35?
(ii) (4 pts) Choose this phosphate species (in i) as the onlyphosphorus component. What amounts of this substance and any otherreagents (grams of solid(s); mL of any solution(s) and water) wouldyou need to make the buffer with pH = 7.35?
(iii)(4 pts) Choose this phosphate species (in i) and either itsconjugate acid or base as the only two phosphorus components. Whatamounts of this substance, its conjugate acid or base, and water(grams of solid(s); mL of any solution(s) and water) would you needto make the buffer with pH = 7.35?
