Environmental Engineering Reference
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2. Explain: (a) why HCl is weaker than HNO 3 used in acid digestion? (b) why dryness
should be avoided in acid digestion and why dryness is particularly harmful if HClO 4 is
used? (c) why HClO 4 should not be used alone for acid digestion?
3. Describe the difference in the acid preservation procedure between total metals and
dissolved metals.
4. Explain why speciation analysis is particularly important for Cr, As, and Se? What are
the major valance (oxidation number) for each of these three elements? Describe their
impact with regard to plant, and animal/human.
5. Describe/define briefly: (a) dissolved metals, (b) alkaline digestion for Cr(VI),
(c) selenate ion vs. selenite ion, (d) arsenate and arsenite.
6. Explain: (a) why a chemical with a Henry's law constant (H)of10 4 atmm 3 /mol
cannot be separated using separate funnel L-L extraction; (b) why a solution containing
a chemical with very high vapor pressure could be low in volatility?
7. Describe how distribution coefficient (D) and the phase ratio affect the extraction
efficiency in the L-L extraction.
8. Describe the operational steps in using Soxhlet extraction.
9. Explain: (a) why acetone or acetonitrile cannot be used in solvent extraction? (b) in
extracting organics from aqueous solutions using separatory funnel, which layer (top or
bottom) should be collected if benzene is used? What if chloroform is used?
10. Explain: (a) why solid phase extraction (SPE) can only be used for liquid samples?
(d) why anhydrous sodium sulfate (Na 2 SO 4 ) is added during solid sample extraction?
(b) why SPME can be used for both liquid and solid samples?
11. Discuss the advantage and disadvantage of the following sample preparation:
(a) conventional Soxhlet extraction, (b) ultrasonic extraction, (c) solid phase extraction,
(d) supercritical fluid extraction.
12. Discuss the advantage of: (a) microwave assisted acid digestion over hotplate digestion,
(b) Soxtec over conventional Soxhlet, (c) pressured fluid extraction over extraction with
ambient temperature and pressure.
13. Why CO 2 in its supercritical state increases the extraction efficiency? What are the major
mechanisms for the enhanced extraction efficiency? Why is a minor amount of solvent
used in the SFE system?
14. Draw a schematic diagram for the supercritical extraction system (SFE).
15. Draw a schematic diagram for the purge-and-trap system with GC as the analytical
instrument.
16. Discuss the principles and compound applicability of the following sample cleanup
procedures: (a) alumina, (b) Florisil, and (c) silica gel.
17. Derivatization is sometimes used prior to HPLC and GC analysis: (a) what are the
purposes of derivatization? (b) what types of compounds (e.g., with certain functional
groups) normally need to be derivatized?
18. Describe: (a) silylation, (b) acylation, (c) esterification.
19. Describe the following and indicate in general what types of contaminants (i.e., with
regard to solubility, volatility, etc) are applicable: (a) dynamic headspace extraction
(purge-and-trap), (b) static headspace extraction, (c) azeotropic distillation, and (d)
vacuum distillation.
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