(a) Explain why the concentration of dissolved oxygen in freshwater is an important indicator of the quality of the water. (b) How is the solubility of oxygen in water affected by increasing temperature?

Dissolved oxygen (DO) is the amount of oxygen that is present in water. It is an important factor in determining the quality of water, as oxygen is essential for the survival and growth of aquatic organisms, such as fish, invertebrates, and bacteria. A healthy water ecosystem requires adequate levels of dissolved oxygen to support its living organisms. Higher concentrations of dissolved oxygen typically represent better water quality, as adequate oxygen levels allow for a diverse range of aquatic life to thrive. In contrast, low oxygen levels can lead to the death of fish and other aquatic life, as they cannot survive in an oxygen-deprived environment. Additionally, low oxygen levels can promote the growth of undesirable organisms, such as some types of bacteria, which can further degrade water quality and contribute to other environmental problems. Water with a high level of oxygen helps in decomposing organic matter and breaking down pollutants more efficiently. Therefore, the concentration of dissolved oxygen in freshwater is an important indicator of the quality of water and the overall health of the aquatic ecosystem.

The solubility of oxygen in water is affected by temperature, among other factors. As the temperature of water increases, the solubility of oxygen decreases, meaning that warmer water holds less dissolved oxygen than colder water. The relationship between temperature and oxygen solubility can be explained by the kinetic energy associated with water molecules. At higher temperatures, water molecules have increased kinetic energy and move more rapidly, which makes it harder for oxygen molecules to interact with water molecules and dissolve. As a result, less oxygen can be dissolved in warmer water than in colder water. Conversely, as the temperature decreases, water molecules move more slowly, and their decreased kinetic energy allows oxygen molecules to interact more easily with water molecules, leading to a higher solubility of oxygen in colder water. This temperature-solubility relationship is significant because it has direct implications for aquatic life and water quality. Warmer water can hold less dissolved oxygen, potentially resulting in reduced oxygen availability for aquatic organisms. In extreme cases, this oxygen depletion can lead to the death of fish and other aquatic life, contributing to the overall degradation of water quality.