Exchangeable Acidity of Soils

The acidity of soils can occur due to various processes that promote a pH reduction. These processes occur naturally or by human action. The main sources of soil acidity are associated to hydrogen ions (H+) and aluminum ions (Al+3) in the soil's solution. Exchangeable acidity is determined through the use of neutral salts solutions such as potassium chloride (KCl). The acid ions (aluminum and hydronium) that are held in the colloidal fraction of the soil, that in the presence of a displacing ion (K+), makes those enter the soil solution. Afterward, that solution is titrated with a sodium hydroxide solution of the exact concentration to reach the last point of the neutralization reaction using phenolphthalein as an indicator.