SOLUTIONS to Separations Practice Problems

SOLUTIONS to Separations Practice Problems - Additional...

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1 E = electric field strength = volts/cm Additional Practice Problems: SEPARATIONS Chem 241-Section 1 Spring 2008 Professor Jorgenson R S = 2t 2 t 1 ( ) W 1 + W 2 V R = V M + KV S H = L N = A + B u + Cu α = K 2 K 1 = k' 2 k' 1 = t 2 t m t 1 t m m m r M S M M S S t t t V V K V C V C k' = = = D = KH + [] K a + H + [ ] D = KK a K a + H + [ ] t r = t m 1 + k' () = L u 1 + K V S V M Q n = V 1 V 1 + KV 2 n K = C organic C aqueous K = C stationary C mobile 1 4 k' 1 k' 1 4 N R ave 2 S + = γ N N = 16R S 2 1 2 1 + k' ave k' 2 2 t' r = t r t m I = 100 n + N n Log t' X Log t' n ( ) Log t' N Log t' n velocity = µ apparent E apparent = ep + eo 2 H 2 r 2 B 2 r 2 t 2 r W t 5.55 W t 16 t N = = = σ 1 2 t t =
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2 0 5 10 D (distribution ratio) pH 7 5 3 9 11 13 AB C D 1. The chart above shows the behavior of a group of weak acids distributing between diethyl ether and an aqueous phase. Using this chart, answer the following questions: A) What is the partition coefficient, K, for compound D? The partition coefficient for compound “D” is about 9 B) What is the acid dissociation constant, K a , for compound A? The acid dissociation constant of compound A is about 10 -3.5 3 x 10 -4 C) All four of these compounds are present in an aqueous solution. Based on the information in this chart, describe the extraction procedure you would use to isolate compound B from all the other compounds in this mixture. Adjust the pH of the aqueous solution to be about 7, and extract with ether. Compounds A and B will remain in the aqueous layer. Then adjust the pH of the aqueous layer to about pH 5, and extract with ether again. This time, compound B will be isolated virtually alone and pure in the ether layer.
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3 2. Benzoic acid is a weak acid with a pK a = 4.20. The partition coefficient of benzoic acid between ether and water is 13.8, favoring ether. A) Draw a graph of the distribution coefficient (distribution ratio) vs. pH for the distribution of benzoic acid between ether and water. Make sure to label the axes of the plot, and indicate any important points or features in your graph.
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SOLUTIONS to Separations Practice Problems - Additional...

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