Conductivity—titration profiles

We know that HCl is a considerably stronger acid as compared to CH COOH. HCl ionizes fully and almost all the hydrogen of HCl is present as H at any point of time. HCl also conducts the electric current much better than CH COOH. The two acids, however, have similar titration profiles. 25 ml of 0.01 N NaOH are required to fully titrate 25 ml of 0.01 N HCl. The same amount of O.OllVNaOH is required to fully titrate 25 ml of O.OIN CH COOH. Both acids give similar titration response because of the following scheme of events. Acetic acid is weakly ionized and only 1.3% of its hydrogen is present as H. When we add alkali to this solution, the OH ions liberated from it combine with the H present and remove them in the form of water. 

Schwertmann, 1993). Such soils are characterized by a hydraulic conductivity somewhere in the profile which is too low to cope with the high rainfall, so that all pores will be filled with water for certain periods of time (see above). In this case, the oxygen supply is limited by the low level of O2 dissolved in the soil water (46 mg O2 at 25 °C) and reduction of Mn-oxides, nitrate and Fe oxides sets in. Soils containing Fe oxides are, therefore, redox-buffered (poised). The redox titration curve (Fig. 16.14) of a soil with 23 g kg Fe as Fe oxides shows buffering at two different pe -1- pH levels, one at ca. 11 and another at ca. 9, which indicate the presence of a more reducible (e. g. ferrihydrite) and a less reducible (e. g. goethite) Fe oxide, respectively, in accordance with their different solubilities (see Chap. 9). 

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