Sedimentation Time Measurements of Soil Particles by Light Scattering and Determination of Chromium, Lead, and Iron in Soil Samples via ICP

A central issue in soil pollution chemistry is how toxic metals such as chromium, arsenic, or lead interact with geosorbents such as soils, clays, and rocks as well as with solid matter suspended in groundwater, that is, colloids. Surfaces of geosorbents and colloids can bind toxic species and also promote reactions that chemically transform toxic species. In this two-part general chemistry laboratory activity, students study soil samples from home and from campus. In part one, the samples are placed in water and the suspended colloid fraction is separated using filtration, followed by a determination of colloid sedimentation rates via light scattering. In part two, the solid phase of the soil samples is dissolved in acid and analyzed for chromium, lead, and iron using an inductively coupled plasma spectrometer. The experiment can be expanded to include arsenic. Through these experiments students can draw conclusions about the physical and chemical behavior of solid components in soil, paying particular attention to their propensity for transporting and chemically transforming pollutants in the environment.