Introduction to Soil Chemistry

ibliography 125
tion analysis. Because of the color of soil and the fact that it is a suspension
when stirred, it is often necessary to remove the constituent of interest before
titration. In other cases it is possible to do a direct titration using an appropriate
indicator. However, even in these cases detection of the endpoint is
difficult.
Because of the complex nature of titration curves obtained using pH, ionselective
electrodes, or mV (Eh) measurements on whole soils, these methods
except for organic matter determination, are seldom used.
PROBLEMS
6.1. Explain why the endpoint of a titration is at neither end of a titration
curve.
6.2. Explain why titration is not a generally useful method for discovering
the acidity of soil.
6.3. Suggest areas in soil where there might be organic matter that is not
determined by dichromate oxidation (refer to earlier chapters).
6.4. Make a flow diagram that shows how to determine all different forms of
nitrogen found in soil.
6.5. Look up the titrimetric method for the determination of cyanide and
describe it.
6.6. Give the equation for the reaction of carbonate with acid. Describe two
ways in which titration might be used to determine carbonate.
6.7. In environmental analysis 15N can be used to determine where nitrogen
moves in the environment.Tell how 15N containing inorganic compounds
might be isolated from soil and how it could be specifically determined.
(Note: You might wish to consult Chapters 7–9 in answering this
question.).
6.8. Describe pH–stat titration in detail.
6.9. Describe the two types of information that can be obtained about a reaction
by using the pH–stat method of titration.
6.10. During most titrations the solution or suspensions are mixed sometimes
continuously. Considering this, why might it be a good idea to use an
indicator during a compleximetric titration?
BIBLIOGRAPHY
U.S. Environmental Protection Agency. Test Methods. SW-846 on-line,
http://www.epa.gov/epaoswer/hazwaste/test/9_series.htm.
Harris, DC. Quantitative Chemical Analysis, 5th ed. New York: Freeman, 1999.