Copyright© by Houghton Mifflin Company. All rights reserved. Chapter 15 Solutions

Copyright© by Houghton Mifflin Company. All rights reserved.2 Solutions = homogeneous mixture; a mixture in which the components are uniformly intermingled. All parts are the same; completely mixed. Solutions can be solids, liquids, or gases. Solid solution = brass (copper = zinc) Solvent = largest amount of substance present Solutes = other substances in solution Aqueous solutions = water is solvent

Copyright© by Houghton Mifflin Company. All rights reserved.3 Figure 15.7: Steps involved in the preparation of a standard aqueous solution.

Copyright© by Houghton Mifflin Company. All rights reserved.4

Solubility of ionic substances What is an ionic substance? A substance containing anions (-) and cations (+) that dissolve in water, separating the ions and thus able to conduct an electric current.

Copyright© by Houghton Mifflin Company. All rights reserved.6 Figure 15.1: Dissolving of solid sodium chloride.

Copyright© by Houghton Mifflin Company. All rights reserved.7 Solid state ions are packed closely together. Each polar water molecule attaches itself to a sodium ion or a chloride ion. What does polar mean? One side positive and one side negative. What part of the water molecule attached to the sodium ions? The oxygen, the negative side.

Copyright© by Houghton Mifflin Company. All rights reserved.8 Figure 15.2: Polar water molecules interacting with positive and negative ions of a salt.

Copyright© by Houghton Mifflin Company. All rights reserved.9 Solubility of Polar substances Polar substances contain a polar bond which makes it able to dissolve in water. Sugar and ethanol are polar substances. They have an O-H bond where the H can bond with the water molecule.

Copyright© by Houghton Mifflin Company. All rights reserved.10 Figure 15.3: The ethanol molecule contains a polar O—H bond.

Copyright© by Houghton Mifflin Company. All rights reserved.11 Figure 15.3: The polar water molecule interacts strongly with the polar O—H bond in ethanol.

Copyright© by Houghton Mifflin Company. All rights reserved.12 Figure 15.4: Structure of common table sugar.

Copyright© by Houghton Mifflin Company. All rights reserved.13 Substances insoluble in water Petroleum does not dissolve in water. C and H form non polar bonds because C and H have similar electronegativities. Nonpolar bonds are non-compatible with the polar bonds in water. **Like substances dissolve.

Copyright© by Houghton Mifflin Company. All rights reserved.14 Figure 15.5: A molecule typical of those found in petroleum.

Copyright© by Houghton Mifflin Company. All rights reserved.15 Figure 15.6: An oil layer floating on water.

Copyright© by Houghton Mifflin Company. All rights reserved.16 Which substance is soluble and which is insoluble?

Copyright© by Houghton Mifflin Company. All rights reserved Solution Composition The amount of a substance that will dissolve in a solvent is referred to as its solubility. Many factors affect solubility, such as temperature and, in some cases, pressure. – There is a limit as to how much of a given solute will dissolve at a given temperature. A saturated solution is one holding as much solute as is allowed at a stated temperature. Unsaturated = not holding as much as allowed.

Copyright© by Houghton Mifflin Company. All rights reserved.18 Figure 12.3: Comparison of unsaturated and saturated solutions.

Copyright© by Houghton Mifflin Company. All rights reserved.19 Solubility: Saturated Solutions Sometimes it is possible to obtain a supersaturated solution, that is, one that contains more solute than is allowed at a given temperature. Supersaturated solutions are unstable. If a small crystal of the solute is added to a supersaturated solution, the excess immediately crystallizes out.

Copyright© by Houghton Mifflin Company. All rights reserved.20 Figure 12.4: Crystallization begins. Photo courtesy of James Scherer.

Copyright© by Houghton Mifflin Company. All rights reserved.21 Amount of substance can vary. Concentrated = a relatively large amount of solute Dilute = a relatively small amount of solute

Copyright© by Houghton Mifflin Company. All rights reserved Factors Affecting Rate of Dissolving 1. Surface area – the more surface area exposed, the faster the substance is dissolved 2. Stirring – exposed new surfaces 3. Temperature – molecules move faster thus dissolve faster.

Copyright© by Houghton Mifflin Company. All rights reserved Solution Composition: Mass Percent The mass percentage of solute is defined as: For example, a 3.5% sodium chloride solution contains 3.5 grams NaCl in grams of solution.

Copyright© by Houghton Mifflin Company. All rights reserved Molarity Easier to use volume instead of mass. Concentration = the amount of solute in a given volume of solution. Concentration = M (Molarity) Standard solution = a solution whose concentration is accurately known.

Copyright© by Houghton Mifflin Company. All rights reserved Molarity The molarity = the number of moles of solute per volume (liters) of solution. For example, 0.20 mol of ethylene glycol dissolved in enough water to give 2.0 L of solution has a molarity of

Copyright© by Houghton Mifflin Company. All rights reserved.26 Figure 15.8: Process of making 500 mL of a 1.00 M acetic acid solution.

Copyright© by Houghton Mifflin Company. All rights reserved.27 Figure 15.9: A bubble in the interior of liquid water surrounded by solute particles and water molecules.

Copyright© by Houghton Mifflin Company. All rights reserved.28 Figure 15.10: Pure water.

Copyright© by Houghton Mifflin Company. All rights reserved.29 Figure 15.10: Solution (contains solute).