Chapter 8. Solutions. Gas Liquid Solid

Transcription

1 1 Chapter 8 Solutions Gas Liquid Solid

2 2 Ch 8.1 Characteristics of Solutions A solution is a mixture Two or more substances; each retains its own identity Composition can vary Properties can vary with Uniform properties throughout One visible phase Can be separated by means

3 3 Solvent Solute quantity same phase as solution quantity material dissolved in solvent Figure 8.1 colored crystals (solute) dissolve in clear liquid (solvent) to produce a solution.

4 4 Ch 8.2 Solubility is the maximum amount of solute that will dissolve in a given amount of solvent under a given set of conditions. Factors affecting solubility of solute & solvent Temperature Pressure (in case of gases) Presence of other

5 5 Most solids become soluble in water with increasing temperature. Table 8.1

6 6 The solubility of a gas in water with increasing temperature. Fish kill as a result of oxygen depletion.

7 7 Effect of Pressure on Solubility of Gases Henry s Law William Henry The amount of a gas that will dissolve in a liquid at a given temperature is directly proportional to the pressure of the gas above the liquid.

8 The larger oxygen partial pressure in an oxygen-enriched mixture translates into increased oxygen uptake. 8

9 9 Decompression Sickness (divers' disease, the bends or caisson disease) describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization. Most commonly a type of scuba diving hazard but may be experienced in caisson working, flying in unpressurised aircraft, and extra-vehicular activity from spacecraft. Scuba divers making a decompression stop Decompression chambers.

10 A saturated solution contains the amount of solute that can be dissolved under a given set of conditions. Figure 8.3 In a saturated solution, the dissolved solute is in dynamic equilibrium with undissolved solute. 10 Example: NaCl(s) + H 2 O(l) dissociation Na + (aq) + Cl - (aq)

11 A supersaturated solution is an unstable solution that temporarily contains more dissolved solute than that present in a saturated solution. It will produce crystals rapidly, often in a dramatic manner, if it is slightly disturbed or if it is with a tiny crystal of solute. 11

12 12 Unsaturated solution contains than the maximum amount of solute Concentrated solution contains a large amount of solute relative to the amount that could dissolve Dilute solution contains a amount of solute relative to the amount that could dissolve

13 13 Ch 8.3 Solution Formation Fig. 8.5 An ionic compound dissolves in H 2 O to form ions.

14 Energy is needed to overcome forces: Attraction between solute particles (ionic bonds for ionic compounds) Attraction between solvent particles (hydrogenbonding for water molecules) Energy is released from the solvation of the ions. The overall process can be exothermic or. Instant Cold Pack NH 4 NO 3 + H 2 O Endothermic Instant Hot Pack CaCl 2 or MgSO 4 + H 2 O 14

15 15 Supplemental material: Entropy The universe has a tendency to move towards disorder. Throw a deck of cards and they will fall in a disorderly heap, not assembled according to suit. When disorder increases, we say entropy.

16 When salts dissolve in water, disorder/entropy. Salts that dissolve in an endothermic process (such as in the Instant Cold Pack) do so because the change in entropy is sufficiently favorable to counterbalance the unfavorable change in enthalpy (heat of solution). 16

17 17 Ch 8.4 Solubility Rules A. Gases mix with each other in all proportions. Neither liquids nor solids can be solutes in air. Fog and smoke are colloids, not. B. Ionic solutes in water Table 8.2 Solubility guidelines for ionic compounds in water.

18 C. Molecules as solute and solvent The generalization is a good tool to predict solubility behavior when molecules are involved. 18 Water, which is a polar solvent, is a good solvent for polar solutes, ionic compounds, and substances that produce ions in water. It is not a good solvent for nonpolar molecules. Figure 8.6 Oil and H 2 O have different and are relatively insoluble in each other.

19 19 Molecules that mix in all proportions are miscible. CH 3 CH 2 -OH + H 2 O are miscible because of.

20 Compared to ethanol, n-hexanol s solubility in water is much lower (0.59g/100mL at 20 o C) because of its long hydrocarbon chain. CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -OH 20 Hydro portion (nonpolar), no interaction with water Hydro polar & attracted to water

21 Sodium stearate has an 18-carbon, hydrophobic and a charged hydrophilic group. It forms micelles in 21 aqueous solution and is the major component of soaps along with many types of solid deodorants, rubbers, latex paints, inks. A typical micelle in aqueous solution. The hydrophobic head groups are in contact with water, sequestering the hydrophobic single tails in the micelle center.

22 22 Nonpolar solvents, will readily dissolve solutes. Fat-soluble vitamins (A, D, E, K), for example, have nonpolar structures that are compatible with the nonpolar nature of fats. The hydrophobic character of the fat-soluble vitamins determines their.

23 23 Drill problem. Name the following molecules and predict which will dissolve in H 2 O. Explain your predictions. NH 3 CH 4 CCl 4 LiNO 3

24 24 Ch 8.5 Solution Concentration Units Percent Concentration % by mass = mass of solute x 100 total mass of solution mass of solution = mass solute + mass solvent units are usually in grams and abbreviated as % (m/m) or w/w % Sample calculation: What is the w/w % of a solution prepared by dissolving 6.4 g NaCl in g water? 6.4g NaCl x 100 = 6.4g NaCl x g NaCl + g H 2 O g solution = % NaCl

25 25 % by volume = volume of solute x 100 volume of solution units are usually in ml and abbreviated as % (v/v) A 5% (v/v) alcohol-in-water solution contains 5.0 ml of alcohol to a total volume of 100 ml with water.

26 26 When volumes of two different liquids are combined, the volumes are not. Figure 8.7 Figure 8.8 The combined volumes or alcohol and water are less than the sum of the individual volumes. 50 ml alcohol + 50 ml water = ml solution

27 27 Percent by volume is the commonly used unit on labels of alcohol-containing products. Many countries also use a measure called a standard drink. In the USA, it is any drink that contains about 14 g of pure alcohol, which is thought to be the amount that an average liver can metabolize in one hour. The purpose of the standard drink measure is to help drinkers monitor and control their alcohol intake. Sample calculation: How many ounces of wine (12 % v/v) are in one standard drink? 12 ml pure alcohol in 100 ml wine Density of pure alcohol = g/ml 1 ounce = ml g alcohol ml alcohol ml wine ounces wine 14 g alcohol x 1 ml x 100 ml wine x 1 oz. 1 standard drink g 12 ml alcohol ml = oz of wine/standard drink

28 28 Examples of one standard drink: 40% 12% 5% (v/v) Proof (a standard of alcohol strength) = 2 x % (v/v) Historically, proof was defined as the most dilute spirit that would sustain combustion of gunpowder (57.15 % v/v).

29 Mass-Volume % = mass of solute (g) x 100 volume of solution (ml) The units are specified in grams and ml because they. The abbreviation is % (m/v) or w/v %. Normal saline is the commonlyused term for a solution of 0.9 % w/v of NaCl. It contains 0.9 g NaCl in 100 ml of aqueous solution. Sample calculation: How many grams of NaCl are present in 1.0 L of normal saline solution? 1.0 L soln x 10 3 ml x 0.9 g NaCl = NaCl 1 L 100 ml soln 29

30 30 Supplemental material: Parts-per notation is used when particularly low concentrations are involved. Parts-per-million ppm = mass or volume of solute x 10 6 mass or volume of solution ppb parts-per-billion, 1 part in ppt parts-per-trillion, 1 part in

31 31 Chemists prefer to use the concentration unit of Molarity. Molarity (M) = moles of solute L of solution Sample calculation: How many grams of solute are contained in L of 0.10 M KCl? (F.W amu) L KCl solution mol KCl g KCl L x 0.10 mole KCl x g KCl = g KCl L mol

32 32 Drill problem: A particular reaction requires g Ca 2+. What volume of 2.0 M CaCl 2 is needed to provide that amount? g Ca 2+ mol Ca 2+ mol CaCl 2 volume soln Ca 2+ x 1 mol x 1 mol CaCl 2 x 1 L g 1 mol Ca mol CaCl 2 = L or 24 ml

33 33 Ch 8.6 Dilution Figure 8.9 Frozen orange juice concentrate is diluted with water prior to drinking. Figure 8.4 Both solutions contain the amount of solute. concentrated stock solution dilute solution A simple relationship exists between the concentrations (C) and volumes (V) of the two solutions (soln). C stock soln x V stock soln = C dilute soln x V dilute soln

34 34 Practice calculation. If 50 ml of a stock solution of 1.0 M KBr are diluted to a volume of 1.0 L, what will be the final concentration of the dilute solution of KBr? C s x V s = C d x V d (you must know this equation) 1.0 M x 50 ml = C d x units must cancel C d = M KBr This is a 20-fold dilution of the stock solution.

35 Practice problem: How much water must be added to 100 ml of M NaCl to prepare a M NaCl solution? 35 C s x V s = C d x V d (you must know this equation) M x 100 ml = M x V d V d = 600 ml = final volume (V s + V water ) V water = V d V s = 600 ml 100 ml = 500 ml Q: How many-fold of a dilution has occurred?

36 36 Ch 8.7 Colloidal Dispersions and Suspensions Milk is NOT a solution but a. Colloidal dispersions light (Tyndall effect), true solutions do not.

37 37 Table 8.4 Property comparison for solutions, colloidal dispersions, and suspensions. Examples of Colloids

38 Ch 8.8 Colligative Properties of Solutions are properties that depend on the number of solute particles in solution, not on their. reduction of vapor pressure elevation of boiling point depression of freezing point osmotic pressure The magnitude of a colligative property is directly proportional to the total concentration of the species formed when solutes dissolve. Example. When 1 mole of CaCl 2 and 1 mole of sugar are dissolved together in water, we have a total of 4 moles of particles: 1 mole CaCl 2 1 mole Ca moles Cl mole sugar 1 mole of molecules. moles of particles 38

39 39 Figure 8.11 Effect of a solute on the vapor pressure of a solvent. pure solvent solution Fewer solvent molecules escape from the solution, resulting in a reduction of the vapor pressure. The greater the concentration of solute particles, the will be the reduction in the vapor pressure.

40 40 Higher temperatures are needed to raise the depressed vapor pressure of a solution to the boiling point elevation of the boiling point. An increase in the b.p. of a solvent is directly proportional to the concentration of solute particles. Example: The boiling point of water increases by 0.52 o C per mole of solute particles per kilogram of water. If the solute is 1 mole of sugar, the boiling point of the aqueous solution is o C. Q: What will be the b.p. if the solute is 1 mole of NaCl?

41 41 Figure 8.12 A water-antifreeze mixture has a higher boiling point AND a freezing point than pure water. The depression of the freezing point due to solutes is directly proportional to the total concentration of all the particles dissolved. NaCl/ice 1:3 20 o C

42 42 Freezing Point Depression at the Molecular Level. Ice Melting Freezing Solution At equilibrium: rate of melting = rate of freezing When the rate of freezing of solvent molecules decreases in the presence of solute particles, then the rate of melting must also decrease to establish a new equilibrium. For this to happen, the temperature (m.p. of the solution) must.

43 Ch 8.9 Osmosis and Osmotic Pressure Fig Osmosis is the flow of solvent through a semipermeable membrane from a solution to a more solution. 43 (b) The liquid level rises until equilibrium is reached. At equilibrium, the solvent molecules move back and froth across the membrane at equal rates.

44 44 Figure 8.14 Osmosis at the molecular level. Solute molecules literally interfere with the movement of solvent molecules across the membrane.

45 45 Figure 8.15 Osmotic pressure is the amount of pressure needed to the net flow of solvent across the membrane in the direction of the more concentrated solution. The greater the difference in concentrations between the separated solutions, the the magnitude of the osmotic pressure.

46 Reverse osmosis is used in the desalination of seawater to make drinking water. 46

47 13,080 Desalination plants world-wide produce more than 12 gallons of water a day (according to the International Desalination Association). 47 Reverse osmosis desalination plant in Barcelona, Spain

48 48 Cell membranes in both plants and animals are semipermeable in nature. Figure 8.16 The dissolved substances in tree sap create a more concentrated solution than the surrounding ground water. Water enters membranes in the roots and rises in the tree, creating an osmotic pressure that can exceed 20 atm in extremely tall trees.

49 49 The concentration of solute particle It is distinct from molarity because it measures moles of solute particles rather than of solute. osmolarity = molarity x i s is called osmolarity. i = number of particles produced from the dissociation of one formula unit of solute Example: What is the osmolarity of a solution that is 1 M in MgBr 2 and 2 M in glucose? Osmolarity = 1 M x M x 1 = MgBr 2 glucose

50 The osmotic pressure of a solution is directly proportional to the number of solute particles present. Solution A Solution B 0.30 osmol = 7.6 atm 0.15 osmol = 3.8 atm Solution C 1.5 osmol =? The relationship between osmotic pressure ( ) and the osmolarity of the solute particles resembles the gas law: V = nrt n = number of moles of all solute particles R = universal gas constant 50

51 51 Isotonic, Hypotonic, and Hypertonic solutions pertain to osmotic-type of phenomena that occur in the human body. Fig 8.17 Effects of bathing red blood cells in various types of solutions. A red blood cell in a physiological saline solution ( tonic solution). In pure water ( tonic solution) the red blood cell swells and hemolysis occurs. Shrinking or crenation occurs in a concentrated NaCl solution ( tonic solution).

52 52 Ch 8.10 Dialysis is a process in which a semipermeable membrane allows the passage of solvent, dissolved ions, and small molecules, but blocks the passage of larger particles. Before After Figure 8.18 In dialysis there is a movement of ions.

53 53 Figure 8.19 Impurities (ions) can be removed from a colloidal dispersion by using a dialysis procedure. The Artificial Kidney Hemodialysis Machine