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

2. 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

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

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

5. 5 15.1 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.

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

7. 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.

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

9. 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.

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

11. 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.

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

13. 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.

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

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

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

17. Copyright© by Houghton Mifflin Company. All rights reserved.17 15.2 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.

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

19. 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.

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

21. 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

22. Copyright© by Houghton Mifflin Company. All rights reserved.22 15.3 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.

23. Copyright© by Houghton Mifflin Company. All rights reserved.23 15.4 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 100.0 grams of solution.

24. Copyright© by Houghton Mifflin Company. All rights reserved.24 15.5 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.

25. Copyright© by Houghton Mifflin Company. All rights reserved.25 15.5 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

26. 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.

27. 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.

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

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