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The theoretical limit for extracting solute Sfrom Phase1(volumeV1)into phase2 (volumeV2)is attained by dividing V2into an infinite number of infinitesimally small portions and conducting an infinite number of extractions. With a partition coefficient, K=[S]2/[S]1the limiting fraction of solute remaining in phase 1is2qlimit=e-(V2/V1)K(V1=V2=50mLandK=2). Let volume V2be divided intoequal portions to conduct extractions. Find the fraction of S extracted into phase 2 for n = 1,2, and 10extractions. How many portions are required to attain 95%of the theoretical limit?

Short Answer

Expert verified

To conclude the number of portions required in order to attain the 95% of the limit would be and the extracted fraction would be

0.95×0.864655=0.82143

Step by step solution

01

Given Information:

For Partition coefficient K=S2/S1,the limited fraction of solute in is

1is2qlimit=e-(V2/V1)K(V1=V2=50mLandK=2).The fraction of is extracted for forn=1,2,and10extractions.

02

To Find the fractions of the solute :

Limited fractions of solute remaining in first phase

qlimit=eV2/V1kqlimit=e-50mL/50mL×2qlimit=0.135335

The maximum fraction extracted would be

1-qlimit=1-0.1353351-qlimit=0.864665

S.NO

A

B

C

D

E

F

1

n

V2/n

Q

1-q

% Extracted

2

1

50.0

0.333

0.667

77.1

3

2

25.0

0.250

0.750

86.7

4

3

16.7

0.216

0.784

90.7

5

4

12.5

0.198

0.802

92.8

6

5

10.0

0.186

0.814

94.1

7

6

8.3

0.178

0.822

95.1

8

7

7.1

0.172

0.828

95.7

9

8

6.3

0.168

0.832

96.2

10

9

5.6

0.164

0.836

96.6

11

10

5.0

0.162

0.838

97.0

For column C calculations as q=V1V1+D×V2n

For column D calculations as 1-q

For column E calculations as 1-q1-qlimit

To conclude the number of portions required in order to attain the of the limit would be and the extracted fraction would be

0.95×0.864655=0.82143

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Most popular questions from this chapter

23-32. Chromatograms of compounds A and B were obtained at the same flow rate with two columns of equal length. The value of tmis 1.3m in both cases.


(a) Which column has more theoretical plates?

(b) Which column has a larger plate height?

(c) Which column gives higher resolution?

(d) Which column gives a greater relative retention?

(e) Which compound has a higher retention factor?

(f) Which compound has a greater partition coefficient?

(g) What is the numerical value of the retention factor of peak A?

(h) What is the numerical value of the retention factor of peak B?

(i) What is the numerical value of the relative retention?

A Gas chromatogram of a mixture of toluene and ethyl acetate is shown here:

(a)Use the width of each peak (measured at the base)to calculate the number of theoretical plates in the column. Estimate all lengths to the nearest 0.1 mm.

(b)Using the width of the toluene peak at its base, calculate the width expected at half height. Compare the measured and calculated values. When the thickness of the the line is significant relative to the length being measured, it is important to take the pen line width into account. You can measure from the edge of one line to the corresponding edge of the other line,as shown here.

Isotopic compounds (isotopologues) are separated in Figure 23-15 by repeated passage through a pair of columns. Each cycle in the figure represents

one pass through length L = 25 cm containing

L theoretical plates. The relative retention (α) is and the retention factor for

L-phenylalanine is k2=1.62. (a) The observed resolution after 10 cycles is 1.60 .

Calculate the number of theoretical plates, N , in column length L . The mixture

has passed through length 10L in 10 cycles.

(b) Find the plate height in μ³¾.

(c) Predict the resolution expected from two cycles. The observed value is 0.71 .

If you wish to extract aqueous acetic acid into hexane, is it more effective to adjust the aqueous phase to or ?

23-42. A separation of 2.5mgof an unknown mixture has been optimized on a column of length L and diameter d .

(a) Explain why you might not achieve the same resolution if the 2.5mgof unknown mixture were injected in twice the injection volume.

(b) Explain why you might not achieve the same resolution if5.0mg of unknown mixture were injected in the original injection volume.

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