Introduction to Soil Chemistry

pH
9.5
9
8.5
8
7.5
7
6.5
6
5.5
ph titration of soil 117
Titration of Soil with NaOH
5
0 20 40
Titrant Volume
60
Figure 6.5. Titration of 50g of soil suspended in 50mL of distilled water with 0.1M NaOH using
a pH meter. Titrant was added slowly and continuously with stirring.
titration endpoint is seen here as there is in Figure 6.1. However, it is possible
to determine the amount of base needed to bring this soil to pH 6.5, which is
a typical pH desired for crop production.
This also explains why the pH of any extracting solution is important.
Depending on the pH of the extracting solution, the component(s) of interest
may be in the form of an ion or a polar or neutral molecule.This, in turn, determines
whether it will be solvated by the solvent chosen as the extractant. If a
certain pH is needed for an extraction process, then titration of a soil can be
carried out in order to determine how much base or acid would be needed for
the process. This would be useful in cases where removal of a contaminant
from a spill site or a field is required.
Caution: Lowering or raising a soil’s pH to effect remediation, especially
on a large scale, is not feasible for four reasons: (1) changing
the pH of soil to any great extent requires large amounts of acid or
base because soil is highly buffered, (2) soil is destroyed at both very
high and very low pH levels, (3) a large amount of material that
cannot be readily returned to the environment is produced, and (4)
the material is no longer soil!