1. Chapter 7 Solutions 7.1 Solutions 1

2. Solute and Solvent Solutions are homogeneous mixtures of two or more substances. consist of a solvent and one or more solutes. 2

3. Nature of Solutes in Solutions Solutes spread evenly throughout the solution. cannot be separated by filtration. can be separated by evaporation. are not visible, but can give a color to the solution. 3

4. Examples of Solutions The solute and solvent in a solution can be a solid, liquid, and/or a gas. 4

5. Example Identify the solute in each of the following solutions. A. 2 g of sugar and 100 mL of water B. 60.0 mL of ethyl alcohol and 30.0 mL of methyl alcohol C. 55.0 mL of water and 1.50 g of NaCl D. Air: 200 mL of O 2 and 800 mL of N 2 5

6. Water Water is the most common solvent. is a polar molecule. forms hydrogen bonds between the hydrogen atom in one molecule and the oxygen atom in a different water molecule. 6

7. Formation of a Solution Na + and Cl - ions on the surface of a NaCl crystal are attracted to polar water molecules. are hydrated in solution with many H 2 O molecules surrounding each ion. 7 When NaCl(s) dissolves in water, the reaction can be written as H 2 O NaCl(s) Na + (aq) + Cl - (aq) solid separation of ions

8. Example Solid LiCl is added to water. It dissolves because A. the Li + ions are attracted to the 1) oxygen atom (  - ) of water. 2) hydrogen atom (  + ) of water. B. the Cl - ions are attracted to the 1) oxygen atom (  - ) of water. 2) hydrogen atom (  + ) of water. 8

9. Like Dissolves Like Two substances form a solution when there is an attraction between the particles of the solute and solvent. when a polar solvent such as water dissolves polar solutes such as sugar, and ionic solutes such as NaCl. when a nonpolar solvent such as hexane (C 6 H 14 ) dissolves nonpolar solutes such as oil or grease. 9

10. Like Dissolves Like Like Dissolves Like Solvents Solutes Water (polar) Ni(NO 3 ) 2 CH 2 Cl 2 (nonpolar) (polar) I 2 (nonpolar) 10

11. Example Which of the following solutes will dissolve in water? Why? 1) Na 2 SO 4 2) gasoline (nonpolar) 3) I 2 4) HCl 11

12. 7.2Electrolytes and Nonelectrolytes 12

13. In water, strong electrolytes produce ions and conduct an electric current. weak electrolytes produce a few ions. nonelectrolytes do not produce ions. 13 7.2Electrolytes and Nonelectrolytes

14. Strong Electrolytes Strong electrolytes dissociate in water, producing positive and negative ions. conduct an electric current in water. in equations show the formation of ions in aqueous(aq) solutions. H 2 O 100% ions NaCl(s) Na + (aq) + Cl − (aq) H 2 O CaBr 2 (s) Ca 2+ (aq) + 2Br − (aq) 14

15. Examples Complete each for strong electrolytes in water. H 2 O A. CaCl 2 (s) 1) CaCl 2 (s) 2) Ca 2+ (aq) + Cl 2 − (aq) 3) Ca 2+ (aq) + 2Cl − (aq) H 2 O B. K 3 PO 4 (s) 1) 3K + (aq) + PO 4 3− (aq) 2) K 3 PO 4 (s) 3) K 3 + (aq) + P 3− (aq) + O 4 − (aq) 15

16. Weak Electrolytes A weak electrolyte dissociates only slightly in water. in water forms a solution of a few ions and mostly undissociated molecules. HF(g) + H 2 O(l) H 3 O + (aq) + F - (aq) NH 3 (g) + H 2 O(l) NH 4 + (aq) + OH - (aq) 16

17. Nonelectrolytes Nonelectrolytes dissolve as molecules in water. do not produce ions in water. do not conduct an electric current. 17

18. Examples Classify each of the solute represented in the following equations as a strong, weak, or nonelectrolyte a.NH 4 OH(aq) NH 4 + (aq) + - OH(aq) b.HCl (aq)  H + (aq) + Cl - (aq)

19. Equivalents An equivalent (Eq) is the amount of an electrolyte or an ion that provides 1 mole of electrical charge (+ or -). 1 mole of Na + = 1 equivalent 1 mole of Cl − = 1 equivalent 1 mole of Ca 2+ = 2 equivalents 1 mole of Fe 3+ = 3 equivalents 19

20. Electrolytes in Body Fluids In replacement solutions for body fluids, the electrolytes are given in milliequivalents per liter (mEq/L). Ringer’s Solution Na + 147 mEq/L Cl − 155 mEq/L K + 4 mEq/L Ca 2+ 4 mEq/L The milliequivalents per liter of cations must equal the milliequivalents per liter of anions. 20

21. Examples A. In 1 mole of Fe 3+, there are 1) 1 Eq.2) 2 Eq. 3) 3 Eq. B. In 2.5 moles of SO 4 2−, there are 1) 2.5 Eq.2) 5.0 Eq. 3) 1.0 Eq. C.An IV bottle contains NaCl. If the Na + is 34 mEq/L, the Cl − is 1) 34 mEq/L.2) 0 mEq/L. 3) 68 mEq/L. 21

22. 7.3 Solubility Solubility is the maximum amount of solute that dissolves in a specific amount of solvent. expressed as grams of solute in 100 grams of solvent, usually water. g of solute 100 g water 22

23. Unsaturated Solutions Unsaturated solutions contain less than the maximum amount of solute. can dissolve more solute. 23

24. Saturated Solutions Saturated solutions contain the maximum amount of solute that can dissolve. have undissolved solute at the bottom of the container. 24

25. Examples At 40  C, the solubility of KBr is 80 g/100 g of H 2 O. Identify the following solutions as either 1) saturated or 2) unsaturated. Explain. A. 60 g KBr added to 100 g of water at 40  C. B. 200 g KBr added to 200 g of water at 40  C. C. 25 g KBr added to 50 g of water at 40  C. 25

26. Examples The solubility of NaNO3 in water at 50 o C is 110/100mL. In a laboratory, a student use 50.0 g of NaNO 3 with 200 g of water at the same temperature ◦ How many grams of NaNO 3 will dissovle? ◦ Is the solution saturated or unsaturated? ◦ What is the mass, in grams, of any solid NaNO 3 on the bottom of the container?

27. Effect of Temperature on Solubility Solubility depends on temperature. of most solids increases as temperature increases. Hot tea dissolves more sugar than does cold tea because the solubility of sugar is much greater in higher temperature When a saturated solution is carefully cooled, it becomes a supersaturated solution because it contains more solute than the solubility allows. of gases decreases as temperature increases. At higher temperature, more gas molecules have the energy to escape from the solution Leaving higher pressure inside the container 27

28. Solubility and Pressure Henry’s law states the solubility of a gas in a liquid is directly related to the pressure of that gas above the liquid. at higher pressures, more gas molecules dissolve in the liquid. 28

29. 29 A. Why could a bottle of carbonated drink possibly burst (explode) when it is left out in the hot sun? B. Why do fish die in water that is too warm?Examples

30. Soluble and Insoluble Salts Ionic compounds that dissolve in water => soluble salts Ionic compounds that do not separate into ions in water => insoluble salt How do we know which ionic compounds is soluble or insoluble?

31. Precipitation Reactions and Solubility Guidelines

32. Examples Predict whether the following ionic salt is soluble in water ◦ FeCl 3 ◦ Na 2 CO 3 ◦ AgCl ◦ BaSO 4

33. 7.4 Percent Concentration The concentration of a solution is the amount of solute dissolved in a specific amount of solution. amount of solute amount of solution 33

34. Mass Percent Mass percent (% m/m) is the concentration by mass of solute in a solution. mass percent = g of solute x 100 g of solute + g of solvent amount in g of solute in 100 g of solution. mass percent = g of solute a 100 g of solution 34

35. Calculating Mass Percent The calculation of mass percent (% m/m) requires the grams of solute (g KCl) and grams of solution (g KCl solution). g of KCl = 8.00 g g of solvent (water) = 42.00 g g of KCl solution = 50.00 g 35

36. Example A solution is prepared by mixing 15.0 g of Na 2 CO 3 and 235 g of H 2 O. Calculate the mass percent (% m/m) of the solution. 1) 15.0% (m/m) Na 2 CO 3 2) 6.38% (m/m) Na 2 CO 3 3) 6.00% (m/m) Na 2 CO 3 36

37. Volume Percent The volume percent (% v/v) is percent volume (mL) of solute (liquid) to volume (mL) of solution. volume % (v/v) = mL of solute x 100 mL of solution solute (mL) in 100 mL of solution. volume % (v/v) = mL of solute 100 mL of solution 37

38. Mass/Volume Percent The mass/volume percent (% m/v) is percent mass (g) of solute to volume (mL) of solution. mass/volume % (m/v) = g of solute x 100 mL of solution solute (g) in 100 mL of solution. mass/volume % (m/v) = g of solute 100 mL of solution 38

39. Percent Conversion Factors Two conversion factors can be written for each type of % value. 39 Copyright © 2009 by Pearson Education, Inc.

40. Using Percent Concentration (m/m) as Conversion Factors How many grams of NaCl are needed to prepare 225 g of a 10.0% (m/m) NaCl solution? STEP 1: Given: 225 g solution; 10.0% (m/m) NaCl Need: g of NaCl STEP 2: g solution g NaCl STEP 3: Write the 10.0% (m/m) as conversion factors. 10.0 g NaCl and 100 g solution 100 g solution 10.0 g NaCl STEP 4: Set up using the factor that cancels g solution. 40

41. Example How many milliliters of a 5.75% (v/v) ethanol solution can be prepared from 2.25 mL of ethanol? 1) 2.56 mL 2) 12.9 mL 3) 39.1 mL 41

42. Using Percent Concentration (m/v) as Conversion Factors How many mL of a 4.20% (m/v) will contain 3.15 g of KCl? STEP 1: Given: 3.15 g of KCl(solute); 4.20% (m/v) KCl Need: mL of KCl solution STEP 2: Plan: g of KCl mL of KCl solution STEP 3: Write conversion factors. 4.20 g KCl and 100 mL solution 100 mL solution 4.20 g KCl STEP 4: Set up the problem 42

43. Example How many grams of NaOH are needed to prepare 125 mL of a 8.80% (m/v) NaOH solution? 43

44. Example What is the % m/v of NaOH in a solution prepared by dissovling 12.0 g of NaOH in enough water to make 220.0 mL solution?