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Analytical Chemistry - aqueous solutions

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17. A certain material "X" has an ether/water partition coefficient, KD = 3.3. If 55 mL of 12 ppt aqueous solution is extracted with 6.0 mL of ether, how much X is drawn into the ether layer?

18. The amount of mercury in a freshwater stream is determined by flowing 500 m3 of water through a charcoal filter canister. The charcoal is later extracted with aqueous HNO3 for a total extract volume of 500.00 mL. Assuming the combined capture and extraction efficiency to be 73%, what is the (w/v) concentration of mercury in the stream if the extract measures 50 ppm?

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(17) Partition coefficient(K) = conc.of X in ether/conc. of X in water
Conc. of X in water = (12/1000) x (1000/55) mol/l
= 12/55 mol/l = 0.2182 mol/l
3.3 = conc.of X in ether/conc. of X in water
3.3 x conc. of X in water = conc.of X ...

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Two questions on aqueous solutions and mercury in freshwater.

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4 Analytical Chemistry Questions.

1. If you wish to extract aqueous acetic acid into hexane, is it more effective to adjust the aqueous phase to pH 3 or pH 8?

2. A chromatogram with ideal Gaussian bands has tr = 17.5 min and w 1/2 = 1.50 min. A) How many theoretical plates are present? B) Find the plate height if the column is 10 cm long.

3. Match the terms in the first list with the characteristics in the second list and give an example of how each type of chromatography could be used in analytical chemistry.

1. adsorption chromatography
2. partition chromatography
3. ion-exchange chromatography
4. molecular exclusion chromatography
5. affinity chromatography

a. Ions in mobile phase are attracted to the counterions covalently attached to stationary phase
b. Different-sized solutes penetrate voids in stationary phase to different extents. Largest solutes are eluted first.
c. Solute equilibrates between mobile phase and surface of stationary phase.
d. Solute in mobile phase is attracted to specific groups covalently attached to stationary phase
e. Solute equilibrates between mobile phase and film of liquid attached to stationary phase.

4.Solute S has a partition coefficient of 3.0 between water (phase 1) and chloroform (phase 2) in equation 22-1.

a) Calculate the concentration of S in chloroform if [S (aq)] is 0.015M.
b) If the volume of water is 70.0 mL and the volume of chloroform is 12.0 mL, find the quotient (mol S in chloroform)/(mol S in water).

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