1. Chapter 16 Solution 1

2. Solution Formation The compositions of the solvent and the solute determine whether a sub will dissolve. 2 Nonpolar substances  e.g. oil, wax,  usually dissolve in nonpolar solvents (e.g. gasoline) Polar substances  (e.g. ionic cpds, acids, bases, salts  usually dissolve in polar solvents (e.g. water)

3. Factors Affecting Speed of dissolving Factors that determine how fast (not the amt) a sub dissolves are stirring (agitation) Temperature--heat the particle size (surface area of the dissolving particles)—fine particles 3

4. Solution Formation A cube of sugar in cold tea dissolves slowly. 4

5. Solution Formation Granulated sugar dissolves in cold water more quickly than a sugar cube, especially with stirring. 5

6. Solution Formation Granulated sugar dissolves very quickly in hot tea. 6

7. Solution Formation Stirring and Soln Formation  speeds up the dissolving process because  fresh solvent (water) is continually brought into contact with the surface of the solute (sugar). 7

8. Solution Formation Temperature and Solution Formation  higher temp → heat → higher KE of water molecules → move faster.  …more collision with the solvent molecules 8

9. Solution Formation Particle Size and Soln Formation  granules dissolves more quickly than a sugar cube because  smaller particles expose a much greater surface area to the colliding water molecules. 9

10. Solubility A saturated solution contains the max amt of solute for a given qty of solvent at a given temp and pressure. 10 An unsaturated solution contains less solute than a saturated soln at a given temp and pressure.

11. Solubility In a saturated soln, the rate of dissolving = the rate of crystallization, the total amt of dissolved solute remains constant. 11

12. Solubility The solubility of a sub the amt of solute that dissolves in a given qty of a solvent at a specified temp and (pressure) to produce a saturated soln. 12 Solubility is often expressed in grams of solute per 100 g of solvent. e.g. 10 g of sugar per 100 g of water at 25°C.

13. Solubility 13 2 (l) are immiscible  insoluble in each other. (e.g. water and oil) 2 (l) are miscible  dissolve in each other in all proportions. (e.g. water and alcohol).

14. Solubility Oil and water are immiscible. 14

15. Solubility Vinegar and oil are immiscible. 15

16. Factors Affecting Solubility Factors Affecting Solubility (the amt)  temperature (affects both speed and amt)  solids …  gases …  pressure (affect gases only) 16

17. Factors Affecting Solubility Temperature  High temp increases solubilities of (s) and (l) solutes  High temp decreases solubilities of gaseous solutes 17 Pressure (gaseous solutes only)  Higher pressure increases the solubility of gases… (directly proportional) e.g. bottled soda …

18. Factors Affecting Solubility Temperature  solubility of most (s) sub increases as the temp of the solvent increases.  solubilities of most gases are greater in cold water than in hot.  e.g. open the lid of a can of soda, put it under the sun for 30 minutes …. 18

19. Factors Affecting Solubility Crystals begin to form in the soln immediately after the addition of a seed crystal. 19

20. Factors Affecting Solubility A supersaturated soln is clear before a seed crystal is added. 20

21. Factors Affecting Solubility Excess solute crystallizes rapidly. 21

22. Factors Affecting Solubility Pressure  (g) solubility increases as the partial pressure of the (g) above the soln increases. 22

23. 23 KCl Temperature in °C

24. 24

25. 25

26. Molarity Concn units can vary greatly. Molarity defined as the # of moles of solute per L of soln. Molarity = # mol solute Volume of solution (L) 1 L solution ≠ 1 L solvent 26

27. Molarity volume → total soln vol that results (not just the volume of solvent alone). Suppose you need 1.0 L of the salt soln. 27

28. Molarity molarity of soln = 0.15M. In order to be at the same [ ] as the salt in the patient’s blood, it needs to have a concn of 0.15 moles of NaCl per L of soln. 28

29. Molarity 0.15M NaCl, where the M stands for “moles/L” and represents the word molar. 29

30. Molarity Need to know 3 things when working quantitatively: (1) the concn (M), (2) the amt of solute (g), and (3) the total vol of soln (L) needed. 30

31. Preparing 1 L of 0.15 M NaCl Solution (1) How to prepare 1.0 L of a 0.15M NaCl soln? 31

32. Preparing 1 L of 0.15 M NaCl Solution (2) thus measure 8.8 g of NaCl 32

33. Preparing 1 L of 0.15 M NaCl Solution (3) (2) Add some H 2 O to dissolve it, and then (3) Add enough additional H 2 O to bring the total vol of the soln to 1.0 L. 33

34. Preparing a Different Vol of a Glucose Soln How would you prepare 5.0L of a 1.5M soln of glucose, C 6 H 12 O 6 ? (1) Determine the # of g of glucose to add to a 5.0-L container. 34

35. Preparing a Different Vol of a Glucose Soln The 1.5M soln must contain 1.5 mol of glucose per L of soln. We need 270 g of glucose for 1 L of solution. 35

36. Add the measured amt of glucose (1350 g) to a 5.0-L container, add enough H 2 O to dissolve the glucose, and fill with H 2 O to the 5.0-L mark. Preparing a Different Vol of a Glucose Soln 36

37. Calculating Molarity Problem: You add 32.0 g of KCl to a container and add enough H 2 O to bring the total soln volume to 955 mL. What is the molarity of this soln? 37

38. Calculating Molarity Molar mass of KCl = 40g + 35g = 75g # moles of KCl = Molarity of KCl = Mass Cl Molar mass KCl KCl 38

39. Example 1 Intravenous saline solutions are often administered to patients in the hospital. One saline solution contains 0.90 g NaCl in exactly 100 mL of solution. What is the molarity of the solution? 39

40. answer 0.15M 40

41. Example 2 Household laundry bleach is a dilute aq soln of sodium hypochlorite (NaClO). How many moles of solute are present in 1.5 L of 0.70M NaClO? How many g of NaClO was used? 41

42. Answer 1.05 moles 42

43. Dilution problems Dilution Add water Volume of solution increases Lower concentration → molarity decreases #mol of solute remains constant → molarity x volume = constant M 1 V 1 = M 2 V 2 43

44. Example 3 How many mL of aq 2.00M MgSO 4 soln must be diluted with water to prepare 100.0 mL of aq 0.400M MgSO 4 ? 44

45. % solutions e.g. in one L of 30% rubbing alcohol contains 300 mL of pure alcohol and 700mL of water % by mass (m/m) = % by volume (v/v) = Volume of solute Volume of solution X 100% Mass of solute Mass of solution X 100% 45

46. ppm Parts per million (parts) [ ] represented by # of parts of solute in one million parts of soln e.g. 56 parts of Cu in 1,000,000 parts of ocean water --- 56 ppm For solutes present in very small amts 46

47. Example 4 What is the % by vol of ethanol in the final soln when 85 mL of ethanol is diluted to a vol of 250 mL with water? 47

48. Example 5 If 10 mL of acetone is diluted with water to a total soln volume of 200 mL, what is the % by volume of acetone in the soln? 48

49. Example 6 How many g of K 2 SO 4 would you need to prepare 1500 g of 5.0% K 2 SO 4 (m/m) soln? 49

50. CST problem 1 How many moles of HNO 3 are needed to prepare 5.0 L of a 2.0 M soln of HNO 3 ? A2.5 B5 C 10 D20 50

51. CST problem 2 The Dead Sea is the saltiest sea in the world. It contains 332 g of salt per 1000 g of water. What is the [ ] in parts per million (ppm)? A0.332 ppm B332 ppm C33,200 ppm D332,000 ppm 51

52. CST problem 3 If the solubility of NaCl at 25°C is 36.2 g/100 g H 2 O, what mass of NaCl can be dissolved in 50.0 g of H 2 O? A18.1 g B36.2 g C72.4 g D86.2 g 52

53. SubstanceFormula/StateSolubility (g/100g H 2 O) Magnesium chlorideMgCl 2 / solid54.6 AmmoniaNH 3 / gas34 EthanolCH 3 CH 2 OH / liquidinfinite Benzoic acidC 6 H 5 COOH / solid0.29 CST problem 4 Which of the substances in the table can act as either the solute or the solvent when mixed with 100 g of water at 20°C? ANH 3 BC 6 H 5 COOH CMgCl 2 DCH 3 CH 2 OH Solubility of substances in water @20°C 53

54. The End 54