Chapter 3 Composition of Substances and Solutions

Chapter Outline

3.1  Formula Mass and the Mole Concept

3.2  Determining Empirical and Molecular Formulas

3.3  Molarity

3.A  Other Units for Solution Concentrations

Lakes have long been a source for drinking water, fishing, and human recreation. However, runoff has brought issues for such activities and resources. Runoff is excess water (usually from rain or snowmelt) that does not absorb into the land surface that carries with it anything that dissolves into the water. Thus, runoff can contain dirt, garbage from the streets, and fertilizers and pesticides used for agriculture that is drained into local bodies of water after rainfall, affecting the level of contaminants. Of specific concern are nitrogen and phosphorous, which are limiting nutrients that cause algae blooms after rain or larger storms. The EPA standard for the amount of nitrate nitrogen in lakes and reservoirs is 10mg/L, and the criterion for phosphorous is 0.10ug/L (United States Environmental Protection Agency)^. If the concentration of nitrogen and phosphorous increases, then algae blooms occur in natural bodies of water, such as Lake Erie (Figure 3.1). Runoff in essential bodies of water, like Lake Erie, pollutes the drinking water for local communities, threatens the wildlife, and prevents people from enjoying recreational activities (Alliance for the Great Lakes). Furthermore, low-income communities are more affected by water pollution due to inequitable funding, sociopolitical factors, and infrastructure. People of color usually reside in lower-income communities compared to white individuals due to systemic injustices, which makes water pollution an issue of both environmental justice and human rights. Regulations and the reduction of farm runoff can allow lakes and other bodies of water to maintain the healthy concentration of nitrogen and phosphorous, preventing algae blooms and thus providing safer, clean water for the local communities. Quantitative aspects of the composition of substances (such as the EPA standard for nitrogen and phosphorous) and mixtures (such as the lake water) are the important topics of this chapter.