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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).


Solution Preview

1) pH=3 would be best because it will cause the acetic acid to be more protonated (more than 99%), which means it will be uncharged and therefore less polar. Less polar means more acetic acid will enter the hexane partition, whereas a pH of 8 ...

Solution Summary

In this solution we explore several analytical chemistry concepts, especially related to chromatography. We talk about efficient extraction and how pH can affect this phenomenon. Next, we calculate theoretical plates and plate height from experimental data. Then we define several different types of chromatography. Finally, we use partition coefficients to calculate concentrations of substances in different solvent phases.