Table of Contents Chapter 11: H2Woes |
|
Chapter ChallengeYou have been assigned by an international health organization, such as UNESCO, to improve the water supplies of communities in Latin America. The communities are of three types: 1.miningand logging areas that have drawn water from mountain streams; 2.farming areas that rely on wells, rivers, swamps, or lakes as sources of water;3.industrializedareas that depend on water reservoirs fed by rivers and wells. You will develop a flow chart for their recommended purification procedures, explain the chemistry behind the procedures, and present your plan to the class. |
|
Activity Summaries |
Chemistry Principles |
Activity 1: What’s in Natural Water? Students learn some of the minerals common to natural waters and that they are composed of ions. They also study the reactions involved when gases dissolve in water and how to measure concentrations. Different sources of pollution, such as agricultural runoff and industrial discharge, are encountered. |
|
Activity 2: Factors Affecting Solubility of Solids Students explore solubility for ionic compounds and develop a set of rules for various combinations of cations and anions. The solubility of covalent compounds is also investigated and the importance of hydrogen bonds is discovered. The effect of temperature on solubility is observed, as well as the exothermic or endothermic nature of solution formation.
|
|
Activity 3: How Much Solute is in the Water? Students learn several common measurements for substances found in water. These include nitrates, iron, and the alkaline earth elements, magnesium and calcium. These quantitative analysis techniques will use colorimetry and titration. |
|
Activity 4: Aqueous Balance: Equilibrium Students generate calcium oxalate in a micro-lab experiment and calculate the Ksp for the equilibrium. Similarly, the Kw of water is explored. The concept of a shift in equilibrium and methods for causing a shift are learned. |
|
Activity 5: Removing Suspended Particles and Iron As a model, students construct a filtration column using a syringe and use it to filter iron (as its hydroxide) from water. In a second experiment, iron is removed in a batch process and the results of the two experiments are compared. Suspended particles are removed using a gel of aluminum hydroxide. |
|
Activity 6: Water Softening Students study the removal of magnesium and calcium ions in the water softening process using a precipitation reaction. Quantitative results are obtained and compared to removal by an ion exchange resin. |
|
Activity 7: Removing Toxic-Metal Ions Students learn the toxic heavy metals which must be removed from a water supply and what the maximum allowed concentrations are. Copper, cadmium, and nickel are removed as their sulfides by precipitation. Also by precipitation, chromium, lead, tin, or zinc concentrations can be lowered by formation of their hydroxides. |
|
Activity 8: Disinfection Students complete their study of water purification methods by examining the final steps of the process. Bacteria are killed by administering hypochlorite solution and the effectiveness is measured by comparing tests from agar jelly. Other bacteriocides are studied and compared with regard to safety and cost. Finally, the pH is adjusted with acid or base. |
|