Chapter 8 Solutions

1. Chapter 8 Solutions • Definition • A solution is a homogeneous mixture of two or • more different substances • only one phase • composition is variable • almost always clear (transparent) • A solution cannot be separated into its components • by filtration Solute – dissolved substance (smaller amount) Solvent – dissolving medium (larger amount) Solutions can be in gas, liquid or solid phases

2. Types of solutions • a) Solid – liquid • 1. Ionic compound • NaCl in water H2O NaCl Na+ + Cl- breaking of ionic bond Ion-dipole attraction Hydration

3. 2. Covalent compounds sugar in water

4. b. Liquid - liquid C O H and H2O H H H (CH3OH) Polar polar CH3 CH3 H H O H O H O Polar dissolves in polar Nonpolar dissolves in nopolar

5. c. Gas – liquid All gases are slightly soluble in water d. Gas-gas All mixtures of gases are solutions • Solid – solid • Cu (copper) in Au (gold) Alloy Brass (Cu/Zn)

6. Solubility • Soluble – dissolves a large amount • Insoluble – dissolves an negligible amount • Miscible – both components are liquid and can dissolve • (mix) in any proportion • example: H2O and CH3OH • Solubility - # of grams that can be dissolved in 100 g • of solvent at saturation (equilibrium)

7. Figure 8.3 In a saturated solution, the dissolved solute is in equilibrium with the undissolved solute. Example:

8. Table 8.1 Solubilities of Various Compounds in Water at 0oC, 50oC, and 100oC.

9. Unsaturated solution – dissolved amount less than solubility Supersaturated solution - dissolved amount more than solubility Aqueous solution – solution in water

10. D. Factors affecting solubility 1. Nature of solute and solvent In general, for non-ionic solutes, “like dissolves like’. • polar solutes dissolve in polar solvents. • nonpolar solutes dissolve in nonpolar solvents. Ionic compounds do not dissolve in nonpolar solvents Examples CH4 in water? NaCl in octane (nonploar)? CH4OH in water? HCl in water?

11. Solubility Guidelines for common Ionic Compounds in Water. • 1. All compounds containing group IA (Li+, Na+, K+, etc.) and NH4+ are soluble in water. • 2. All nitrates (NO3-) and acetates (CH3COO- orC2H3O-) • are soluble in water. • All chlorides (Cl-), bromides (Br-) and iodides (I-) are soluble in water except those of Ag+, Pb2+ and Hg22+. • All sulfates (SO42-) are soluble except • PbSO4, BaSO4, SrSO4 and CaSO4 • 5. All hydroxides (OH-) are insolubleexceptthose of IA • & Ca(OH)2, Sr(OH)2, Ba(OH)2 • 6. Most other ionic compounds are insoluble in water

12. Solubility except Li+, Na+, K+ and NH4+ soluble NO3-, CH3COO- soluble Cl- , Br-, I- soluble AgX, PbX2, Hg2X2. SO42- soluble PbSO4, BaSO4,CaSO4, SrSO4 OH- insoluble IA, Ca2+, Sr2+, Ba2+ Soluble in water? Soluble in water? K2SO4 NH4MnO4 BaSO4 PbCl2 CuCr2O7 MgSO4 CaCO3 NaCl Fe(NO3)2

13. Which of the following would be expected to be the most soluble in water?

14. 2. Temperature Generally, solubility increases as T increases, except for most gases in liquid where solubility decreases as T increases. Example: O2 in water

16. 3. Pressure (above the surface of the solution) Only affects solubility of gases in liquid. Solubility increase as P increases.

17. E. Concentrations of solutions - amount of solute in certain amount of solvent or solution. a) % by mass (mass-mass %) b) % by volume (V-V %)

18. Figure 8.7 When volumes of two different liquids are combined, the volumes are not additive.

19. Figure 8.8 Identical volumetric flasks are filled to the 50.0-mL mark with ethanol and with water.

20. c) mass-volume % d) parts per million (ppm) e) parts per billion (ppb)

21. Examples If an aqueous solution is 2.5 % w/v in aluminum sulfate, Al2(SO4)3, how many grams of aluminum sulfate are there in a liter of solution? How many grams of zinc fluoride, ZnF2, are required to make a 5.00 % w/v aqueous solution in a 250 mL volumetric flask?

22. e) Molarity, M (molar concentration) # of moles of solute/liters of solution 1L 1 mole NaCl 1 M NaCl solution NaCl Example 1 0.50 mol KOH is dissolved in 2.0L of solution. Find the molarity.

23. Example 2 How many grams of NaCl is needed to make 250 mL of a 0.50 M NaCl solution?

24. Example 3. Make a 500mL of 0.250 M K2Cr2O7 solution MW of K2Cr2O7 = 294.2

25. F. Dilution or MV = n add water M2V2 M1V1 M1V1 = M2V2 In general, C1V1 = C2V2, where C stands for concentration

26. M1V1 = M2V2 Example 1. A 250 mL 2.0M NaOH solution is diluted to 1.0 L. What is the molarity of the final solution? Example 2. What volume of a 5.0M HCl solution would be needed to prepare 2.0 L of a 0.25M HCl solution?

27. G. Colligative properties of solutions A colligative property is a physical property of a solution that depends only on the concentration. a) Lowering of vapor pressure Next day water water sugar in water sugar in water

28. water sugar in water b) Elevation of the Boiling point

29. c) Freezing point (depression) lowering Example: Antifreeze; salt-water.

30. d) Osmosis and Osmotic pressure Semi-permeable membrane H2O solution Osmosis: the flow of solvent through a semipermeable membrane from a dilute to a more concentrated solution. At equilibrium, the molecules move back and forth at equal rates.

31. This measures the osmotic pressure of the solution H2O solution The process is called osmosis Pressure applied to prevent osmosis = osmotic pressure

33. V.P. lowering, B.P. elevation and F.P depression and osmotic pressure depend on the concentration of the solute particles but not on the type of solute. Examples:

34. Example: 1.5 mol of K2CrO4 is dissolved in 1000 g of water. What is the freezing point of the solution? Freezing point (depression) lowering mol of particle =

35. Osmolarity NaCl Na+ + Cl- 1M NaCl 2 mol ions osmolarity = 2M osmolarity = M x i i = # of particles produced from the dissociation of one formula unit of solute H2O Osmolarity in cell = 0.31M (osmol) Osmolarity = 0.31M isotonic solution 5.0% m/v glucose 0.92% m/v NaCl (physiological saline solution)

37. Osmolarity = 0.31M isotonic solution Osmolarity > 0.31M hypertonic solution cell crenation Osmolarity < 0.31M hypotonic solution Burst (hemolysis)

38. Red blood cell in a) isotonic solution b) Hypertonic solution c) Hypotonic solution crenation hemolysis

39. Example Consider the following solutions 1M sugar 2M NaCl 1.5M Na2SO4 1M Ca(NO3)2 solution

40. H. Colloidal dispersions A colloidal dispersion is a mixture in which a material is dispersed rather than dissolved. 10-7 – 10-5cm . . . . . . . . . . . . dispersed phase . . . . . . . . . . . . . . . . Cannot be filtered . . . . . . . . . . . . . . . . Dispersing medium

41. solution colloidal dispersion Some proteins have size colloidal dispersion

42. I. Dialysis Dialyzing membrane - has pores large enough to allow some ions and small molecules to pass along with water and gases. Kidney cells, blood capillaries, intestinal walls, etc. function as dialyzing membranes. Dialysis - the movement of ions and small molecules (urea), including water (solvent), across a dialyzing membrane. Large molecules such as proteins cannot pass through a dialyzing membrane.

43. Figure 8.18 In dialysis, there is a net movement of ions from a region of higher concentration to a region of lower concentration. (a) Before dialysis. (b) After dialysis

44. Impurities (ions) can be removed from a solution by using a dialysis procedure.

45. Artificial kidney: a Hemodialysis Machine