Phenylephrine (PE, see the structure below) is a nasal decongestant and is the a

Question

Phenylephrine (PE, see the structure below) is a nasal decongestant and is the active ingredient in Sudafed, which contains phenylephrine hydrochloride (PEHCl). This conjugate acid of phenylephrine (PEH^+) has a pK_a = 5.5. At a physiological pH of 7.4, what is the ratio of concentrations, [PE]/[PEH^+]? a. 6.7 b. 0.01 c. 0.14 d. 79 e. 21 A mining operation needs to separate silver and copper. You are hired as a summer intern in a beautiful Colorado mining town, and one of your tasks is to determine whether this separation can be accomplished by oxidizing the metals to Ag^+ and Cu^+, each one at a concentration of 0.15 M, and then precipitate one as the chloride salt without precipitate the other. AgCl precipitates first. What is the concentration of the Ag^+ remaining in solution when CuCl begins to precipitate? For AgCl, pK_sp = 9.74, and for CuCl, pK_sp, = 6.76. a. 1.57 times 10^-2 M b. 1.57 times 10^-4 M c. 2.23 times 10^-2 M d. 2.23 times 10^-4 M e. 3.72 times 10^-3 M Vitamin C is a monoprotic weak acid, which also is called ascorbic acid (C_6H_8O_5, 176 g/mol). A vitamin C tablet weighing 0.75 g was dissolved in 50.0 mL of water and titrated with 0.250 M sodium hydroxide. It took 12.5 mL of the NaOH solution to reach the end point. What is the percentage of vitamin C in the tablet? Only the vitamin C reacted with the NaOH. a. 98.7% b. 64.2 % c. 87.7 % d. 95.5 % e. 73.3 %

Explanation / Answer

12. d) ie 79

Using Henderson Hesselbach equation of Acidic buffer we get PH=PKa+log[salt]/[Acid]

Putting the values we get log[salt]/[acid]=1.9 or [salt]/[acid=10^1.9=79

14. e) 73.3 %

V1S1=V2S2 now 50*S1(strength of ascorbic acid)=12.5*0.25 or S1=0.0625 M so wt of ascorbic acid=0.0625*176 g=0.55 g so %=0.55/0.75 =73.3

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