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4 Analytical Chemistry Questions.

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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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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.

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the answers may be found in the chemistry and engineering news issues of june 2, 2008(questions1-8) and march 9, 2009(questions 9-10)
look under ACS news (2008 issue) or salary survey (2009 issue) and be sure to check the attached tables.

1. what was the median annual starting salary of 2007 BA/BS chemistry graduates (latest year for which figures are available) with full-time permanent employment and less than 12 months technical work experience prior to graudation?

2. what was the median annual starting salary of 2007 MS and PhD graduates?

3. arrange the following categories of employment in order of decreasing starting salary for BA/BS 2007 chemistry graduates with full-time permanent employment: development and design, management, production/quality control, research, and teaching. What was the spread between the median salaries of the top and bottom of these categories?

4. what percentage of recent year BA/BS chemistry graduates secured either full-or part-time jobs?

5. what percentage of recent year BA/BS chemistry graduates enrolled in graduate or professional schools?

6. what percentage of 2007 BA/BS chemistry graduates who secured any employment started working for each of the following types of employers? industry (include all types), Academia (including high school teaching), Government, Analytical/Clinical labs?

7. what were the 3 most effective job search methods for 2007 BA/BS graduates with full-time employment? give the % of graduates who found jobs these ways?

8. note that the answers to the above questions for 2007 BA/BS graduates are based on the response of a small fraction of graduates. what is this percentage?

9. as of March 2008, what if the median salary of all BA/BS chemists 10-14 years after receiving their degree?

10. answer question 9 for chemists with PhD degrees.

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