16. Analytical chem question on sapling correct answers will get rated! thanks T

Question

16. Analytical chem question on sapling

correct answers will get rated! thanks

The partition coefficient, K, for compound A between toluene and water is 6.95. What is the concentration of A remaining in the aqueous phase after 40.0 mL of 0.360 M A are extracted with the quantities of toluene indicated below?

one 35.0 mL portion . . . [A]1 = ? M

two 17.5 mL portions . . . [A]2 = ? M

Five 7.00 mL portions . . . [A]5 = ? M

Ten 3.50 mL portions . . . [A]10 = ? M

HINT= Calculate the fraction of A remaining in the aqueous phase for each extraction, then multiply this value by the original concentration to determine the concentration remaining.

Explanation / Answer

ANSWER:

The question is based on distribution law and can be solved by using following formulla

Wn = W (KDV / KDV + v)n

Wn = amount of solute left at the end of nth operation

W = amount of solute to be extracted

V = volume of solution

v = volume of other solven

n = nth operation

Moles of A (W) = Molarity X volume

(W) = 0.36 X 40 = 14.4mmoles = 0.0144Moles = 1.44 X 10-2Moles

(i) one 35.0 mL portion

n = 1

v = 35

W1 = W (6.95 X 40  / 6.95 X 40 + 35)1

W1 = 0.888W = 8.88 X 10-2W

W1 = 0.888 X 1.44 X 10-2 = 1.278 X 10-2 M

fraction of A remaining in the aquous phase = (Vaq / KVorg + Vaq)n

Vaq = volume of aquous solution, Vorg = volume of organic solvent

here n = 1

fraction of A remaining in the aquous phase = (40 / 6.95 X 35 + 40) = 0.141 = 1.41 X 10-1

(ii) two 17.5 mL portions

n = 2, v = 17.5

W2 = W (6.95X 40 / 6.95 X 40 + 17.5)2

W2 = 0.885 X 1.44 X 10-2 = 1.274 X 10-2 M

Fraction of A that remains in water = (40 / 6.95 X 17.5 + 40)2

Fraction of A that remains in water = 6.12 X 10-2

(iii) Five 7.00 mL portions

n = 5, v= 7.0mL

W5 = 1.44 X 10-2 (6.95 X 40  / 6.95 X 40 + 7.0)5 = 1.270 X 10-2 M

Fraction Of A in water = (40 / 6.95 X 7.0 + 40)5

Fraction Of A in water = 1.87 X 10-2

(iv) Ten 3.50 mL portions

n = 10, v = 3.5

W5 = 1.44 X 10-2 (6.95 X 40  / 6.95 X 40 + 3.5)10

W5 = 1.27 X 10-2 M

Fraction of A in solution = (40 / 6.95 X 3.5 + 40)10

Fraction of A in solution = 8.6 X 10-2

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