Expt#7. Dissolved Oxygen Level in Natural Waters CHEM 101

CHM 101 Experiment 7 Dissolved Oxygen Levels in Natural Waters Objectives To learn the chemical reactions involved in fixing and analyzing water sample for dissolved oxygen using Winkler method. To determine the dissolved oxygen concentration of a natural water sample. Introduction The aesthetic appearance of bodies of water such as the color, surface growth and odor indicate an immediate perception of the quality of water. Other parameters give clear description of the quality of a water sample such as: pH, dissolved oxygen, alkalinity and hardness. Alkalinity and hardness levels are determined by titrimetric techniques. The level of dissolved oxygen in a water sample is an important factor for the quality of water. Dissolved oxygen refers to the level of free, non-compound oxygen present in water. Oxygen can slowly diffuse into water from the surrounding atmosphere. It is an important parameter in assessing water quality because of its influence on the organisms living within a body of water. The amount of dissolved oxygen is a measure of the biological activity in which high oxygen concentrations indicate aerobic conditions: clean, clear and unpolluted. However, low oxygen concentrations indicate anaerobic conditions: high turbidity, foul odors and extensive plant growth on the surface. It is used as an indicator of the health of a water body. The solubility of free oxygen in water is inversely proportional to temperature and directly proportional to pressure. As the temperature increases, the amount of oxygen decreases, however as the pressure increase the dissolved oxygen increases. Dissolved oxygen level is usually reported in milligrams per liter (mg/L) or ppm. The modern method for dissolved oxygen measurements is done with an instrument known as Dissolved Oxygen Meter. In laboratory, dissolved oxygen is measu