Integrated Science Unit 8, Chapter 23 Unit Eight: Water and the Environment Chapter 23 Water and Solutions 23.1 Water 23.2 Solutions 23.3 Solubility 23.4 Acids, Bases, and pH Chapter 23 Learning Goals Identify and describe the unique properties of water. Describe the shape and polarity of a water molecule. Discuss the nature of hydrogen bonds and their influence on the properties of water. Identify the components of a solution. Categorize mixtures as solutions, suspensions, or colloids. Define solubility. Describe saturated, unsaturated, and supersaturated solutions. Explain how temperature and pressure influence solubility. Understand solubility values. Interpret temperature-solubility graphs. Identify the characteristic properties of acids and bases. Relate the pH scale to examples of acids and bases. Chapter 23 Vocabulary Terms acid alloy base colloid dissociation dissolved electrolyte equilibrium hydrogen bond nanometer neutralization nonpolar molecule pH pH indicator pH scale polar molecule saturated solubility solubility value solute solution solvent suspension supersaturated Tyndall effect unsaturated 23.1 Water A water molecule is made of one oxygen atom that forms a chemical bond with two hydrogen atoms. Because negative charges repel, the four electrons pairs around the oxygen atom are located where they can be the farthest apart from each other. 23.1 Water The geometric shape that allows them to be the farthest apart is called a tetrahedron. In a molecule of water, the electrons are shared unequally between oxygen and hydrogen. 23.1 Water Water is a polar molecule that is, it has a negative end (pole) and a positive end (pole). The oxygen side of the molecule has a partially negative charge and the hydrogen side of the molecule has a partially positive charge. 23.1 Hydrogen Bonding and Water Water molecules behave like a group of magnets. The positive end of one water molecule will align with the negative end of another. The formation of a bond between the hydrogen on one molecule to another atom on another molecule is called a hydrogen bond. hydrogen bonds 23.1 Water Key Question: What are the properties of water? *Read text section 23.1 BEFORE Investigation 23.1 23.2 Solutions A solution is a mixture of two or more substances that is homogeneous at the molecular level. The particles in a solution exist as individual atoms, ions, or molecules. A solution is a mixture of solute dissolved in a solvent. (An alloy is a solution of two or more metals.) Solutions, Solutes and Solvents 23.2 Colloids and Suspensions Colloids and suspensions are not solutions. 23.2 Colloids and Suspensions Colloid particles are formed from clusters of atoms or molecules. Suspensions are mixtures that settle upon standing. Filtering a suspension will separate the different components. 23.2 Solutions Key Question: Can you identify mixtures as solutions, suspensions, or colloids? *Read text section 23.2 BEFORE Investigation 23.2 23.2 Solution Concentrations Molarity is one way of expressing the concentration of a solution. Molarity (M) = Moles of solute Liters of solution 23.2 Solution Concentrations Mass percent is another way to express concentration of solutions. Mass percent = mass of solute x 100% tot. mass of solution 23.3 Solubility The term solubility means the amount of solute that can be dissolved in a specific volume of solvent under certain conditions. Several factors affect solubility: — chemical nature of the solvent — the volume of solute — temperature 23.3 Solubility of Gases The solubility of gases in liquids decreases as temperature increases. The solubility of a gas also depends on pressure. 23.3 Solubility Key Question: What factors affect solubility? *Read text section 23.3 BEFORE Investigation 23.3 23.4 Acids, Bases, and pH Key Question: What is pH? *Read text section 23.4 AFTER Investigation 23.4 23.4 Acids, Bases, and pH Acids An acid is any substance that produces hydronium ions (H3O+) when dissolved in water. They react with metals to produce hydrogen gas (H2) They change the color of a plant dye (called litmus) from blue to red. 23.4 Acids, Bases, and pH Bases A base is any substance that produces hydroxide ions (OH-) when dissolved in water. While you should never touch a laboratory chemical, the bases you use every day such as soap, have a slippery feel. They change the color of litmus from red to blue. 23.4 Acids and bases in your body It is very important for your blood pH to stay within the normal range. The rate at which you breathe controls the concentration of carbon dioxide in your blood.