Presentation is loading. Please wait.

Presentation is loading. Please wait.

Solutions Unit 12: Properties of Solutions Dr. Jorge L. Alonso Miami-Dade College – Kendall Campus Miami, FL Textbook Reference: Chapter # 14 Module #

Similar presentations


Presentation on theme: "Solutions Unit 12: Properties of Solutions Dr. Jorge L. Alonso Miami-Dade College – Kendall Campus Miami, FL Textbook Reference: Chapter # 14 Module #"— Presentation transcript:

1 Solutions Unit 12: Properties of Solutions Dr. Jorge L. Alonso Miami-Dade College – Kendall Campus Miami, FL Textbook Reference: Chapter # 14 Module # 2 CHM 1046: General Chemistry and Qualitative Analysis

2 Solutions Solutions (soln) are homogeneous mixtures of two or more pure substances. The solvent (solv) is present in greatest abundance. All other substances are solutes (solu). Volumetric flask {PrepASolu}

3 Solutions Solutions are homogeneous mixtures of two or more pure substances. In a solution, the solute ( 50%). Homogeneous Heterogeneous

4 Solutions Student, Beware!: solution vs. reaction Just because a substance disappears when it comes in contact with a solvent, it doesn’t mean the substance dissolved. Dissolution is a physical change—you can get back the original solute by evaporating the solvent. If you can’t, the substance didn’t dissolve, it reacted. Mg (s) + 2 HCl (aq)  H 2 (g) + MgCl 2 (aq) Cu(NO 3 ) 2 (s) Cu(NO 3 ) 2 (aq) H2OH2O H2OH2O

5 Solutions How Does a Solution of Salts in Water Form? NaCl (s) Na + (aq) + Cl - (aq) dissociation + H 2 0 The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles. Example: {NaCl + H 2 O*}

6 Solutions Solubility in water Covalent Compounds: many are insoluble gases, polar covalent are mostly soluble. Ionic Compounds: many are soluble. SOLUBILITY RULES: for Ionic Compounds (Salts) 1.All salts of alkali metals (IA) are soluble. 2.All NH 4 + salts are soluble. 3.All salts containing the anions: NO 3 -, ClO 3 -, ClO 4 -, (C 2 H 3 O 2 - ) are soluble. 4.All Cl -, Br -, and I - are soluble except for Ag +, Pb 2+, and Hg 2 2+ salts. 5.All SO 4 2- are soluble except for Pb 2+, Sr 2+, and Ba All O 2- are insoluble except for IA metals Ca 2+, Sr 2+, and Ba 2+ salts. {Soluble metal oxides form hydroxides: CaO Ca OH - } 7. All OH - are insoluble except for IA metals, NH 4 + & slightly soluble Ca 2+ Ba 2+ & Sr 2+ 6.All salts containing the anions: CO 3 2-, PO 4 3-, AsO 4 3-, S 2- and SO 3 2- are insoluble except fro IA metals and NH 4 + salts. 7. For salts containing the anions not mentioned above (e.g., CrO 4 2-, Cr 2 O 7 2-, P 3-, C 2 O 4 2- etc.) assume that they are insoluble except for IA metals and NH 4 + salts, unless, otherwise informed. H2OH2O Elements: mostly insoluble solids, liquids & gases.

7 Solutions Energetics of Solutions Heats (Enthalpy) of Solution (  H soln ) Exothermic solution process NH 4 NO 3 (s) NH 4 + (aq) + NO 3 - (aq) CaCl 2 (s) Ca 2+ (aq) + 2Cl - (aq) H2OH2O Endothermic solution process CaCl 2 + H 2 O NH 4 NO 3 +H 2 O  H soln = kJ/mol + Heat  H soln = kJ/mol Heat + H2OH2O Hot & Cold Packs

8 Solutions (3) Formation of Ion-dipole interactions How Does a Solution Form? (3 events) If an ionic salt is soluble in water, it is because the ion-dipole interactions are strong enough to overcome the lattice energy of the salt crystal.  H Lattice Energy +788 kJ/mol Endothermic NaCl Crystal Lattice H- bonding H2OH2O  H vap +41 kJ/mol Endothermic Energy of Solution  H soln = + or - (1) Separation of solute molecules (2) Separation of solvent molecules Exothermic

9 Solutions Energy Changes in Solution The enthalpy change of the overall process depends on  H for each of these steps. {EnerSoln} -+

10 Solutions Exothermic solution process Endothermic solution process NH 4 NO 3 (s) NH 4 + (aq) + NO 3 - (aq)  H soln = kJ/mol CaCl 2 (s) Ca 2+ (aq) + 2Cl - (aq)  H soln = kJ/mol H2OH2O H2OH2O Why do Endothermic Reactions occur Spontaneously?

11 Solutions Concentration of Solutions (General) Saturated  Solvent holds as much solute as is possible at that temperature.  Dissolved solute is in dynamic equilibrium with solid solute particles. Unsaturated  Less than the maximum amount of solute for that temperature is dissolved in the solvent. {UnsatSoln} Solubility of NaCl in H 2 O = 35.9 g/100 mL (25 °C) NaC 2 H 4 O 2 = 76 g/100 ml (0°C)

12 Solutions Supersaturated  Solvent holds more solute than is normally possible at that temperature.  These solutions are unstable; crystallization can usually be stimulated by adding a “seed crystal” or scratching the side of the flask. {*SuperSat1}SuperSat1 {*SuperSat2} Concentration of Solutions (General)

13 Solutions 1.Polarity 2.Temperature Factors Affecting Solubility A. Solids and Liquids: B. Gases : 1.Molar Mass 2.Pressure – Henry’s Law 3.Temperature

14 Solutions {Water + Oil} Factors Affecting Solubility of Solids and Liquids: (1) Polarity Chemists use the axiom “like dissolves like”:  Polar substances tend to dissolve in polar solvents.  Nonpolar substances tend to dissolve in nonpolar solvents. [Know molecular shapes and polar molecules] (hydrocarbon chain) hydrophobic water- hating, nonpolar, hydrophilic water- loving, polar,

15 Solutions Chemists use the axiom “like dissolves like”:  Polar substances tend to dissolve in polar solvents.  Nonpolar substances tend to dissolve in nonpolar solvents. Factors Affecting Solubility of Solids and Liquids: (1) Polarity [Know molecular shapes and polar molecules] Polar heads Non-Polar tails Polar Non- Polar

16 Solutions Glucose (which has hydrogen bonding) is very soluble in water, while….. Factors Affecting Solubility of Solids and Liquids: (1) Polarity …..cyclohexane (which only has dispersion forces) is not.

17 Solutions Vitamin A is soluble in nonpolar compounds (like fats). Vitamin C is soluble in water. {*Iodine + Water then + CCl 4 } Factors Affecting Solubility of Solids and Liquids: (1) Polarity

18 Solutions Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature. Factors Affecting Solubility of Solids and Liquids: (2) Temperature

19 Solutions Factors Affecting Solubility of Gases in Solution: (1) Molar Mass Larger molecules have stronger London dispersion forces. In general, the solubility of gases in water increases with increasing molar mass. g-MM 28 g/n 32 g/n 40 g/n 84 g/n Why? Which gas dissolves best in water?

20 Solutions Factors Affecting Solubility of Gases in Solution: (2) Pressure {Henrys Law} The solubility of liquids and solids does not change appreciably with pressure. The solubility of a gas (S g ) in a liquid is directly proportional to its pressure (P g ). S g P g

21 Solutions Henry’s Law: where S g is the solubility of the gas; P g is the partial pressure of the gas above the liquid. k is the Henry’s law constant for that gas in that solvent; S g = kP g Factors Affecting Solubility of Gases in Solution: (2) 25 0 C, P N 2 = 0.75 atm, S N2 = M. What is S N2 when P N2 = 1.50 atm? Ans.= M PgPg SgSg {movie} S g P g

22 Solutions The opposite is true of gases:  Gases in carbonated soft drinks are less soluble when warmed.  Warm lakes have less O 2 dissolved in them than cool lakes. Factors Affecting Solubility of Gases in Solution: (3) Temperature

23 Solutions Colligative Properties Pure Solvent Solution: Solvent + Solute How does the presence of a solute change the properties of a solvent? 1.Vapor pressure? 2.Boiling point? 3.Freezing (melting) point? 4.Osmotic pressure?

24 Solutions Colligative Properties Properties that depend only on the CONCENTRATION (number of solute particles present), not on the identity of the solute particles. Pure solventSolvent + Solute 1. Vapor pressure lowering 2. Boiling point elevation 3. Freezing point depression 4. Osmotic pressure P A = X A  P  A  T b = K b  m Tf = Kf  mTf = Kf  m  = MRT

25 Solutions Ways of Expressing Concentrations of Solutions (1) Mass Percentage (%) (2) Parts per Million (ppm) & Parts per Billion (ppb) (3) Mole Fraction (X) (4) Molarity (M) (5) Molality (m)

26 Solutions ppm = mass of solu A in solution total mass of solution  10 6 Parts per Million (ppm) ppb = mass of solu A in solution total mass of solution  10 9 Mass % of A = mass of solu A in solution total mass of solution  100 or 10 2 Mass Percentage (%) (parts per Hundred) 50. g of NaCl in 100.mL of H 2 O g of NaCl in 100.mL of H 2 O 0.000,000,5 g of NaCl in 100.mL of H 2 O Parts per Billion (ppb) hundred million billion

27 Solutions moles of substance A total moles in solution (A+B+∙∙∙) X A = Mole Fraction (X) You can calculate the mole fraction of either the solvent or of the solute — make sure you find the one you need for your calculations! What are the mole fractions of methanol and water in a solution containing 128g CH 3 OH (MW=32.0) and 202 mL of H 2 O (MW=18.0)? Which is the solute and the solvent? Mole fraction of Solvent: Mole fraction of Solute:

28 Solutions mol of solute L of solution M = Molarity (M) Because volume is temperature dependent, molarity can change with temperature. {The volume of most substances expand with increasing temperature} What is the molarity of a solution containing 128g CH 3 OH (MW=32.0,  C) and 202 mL of H 2 O (MW=18.0,  C)?

29 Solutions moles of solute kg of solvent m = Molality (m) Because both moles and mass do not change with temperature, molality (unlike molarity) is not temperature dependent. What is the molality of a solution containing 128g CH 3 OH (MW=32.0,  C) and 202 mL of H 2 O (MW=18.0,  C)?

30 Solutions Problem: What is the molality (m) of a 2.0M NaCl solution at 25 0 C if its density is 1.2 g/mL? Changing Molarity to Molality If we know the density of the solution, we can calculate the molality from the molarity, and vice versa. mol of solute L of solution M = mol of solute kg of solvent m = = 1.8 m NaCl

31 Solutions Colligative Properties Properties that depend only on the number of solute particles present, not on the identity of the solute particles. Pure solventSolvent + Solute 1. Vapor pressure lowering 2. Boiling point elevation 3. Freezing point depression 4. Osmotic pressure P A = X A  P  A  T b = K b  m Tf = Kf  mTf = Kf  m  = MRT

32 Solutions 1. Vapor Pressure ( P vap ) Lowering Because of solute-solvent intermolecular attraction, higher concentrations of nonvolatile solutes make it harder for solvent to escape to the vapor phase. Therefore, the vapor pressure of a solution (P A ) is lower than that of the pure solvent (P  A ). {PureSolv} {*Solution} P A = X A  P  A

33 Solutions Raoult’s Law: P A = X A P  A where X A is the mole fraction of solvent A P  A is the normal vapor pressure of the pure solvent A at that temperature P A is the new vapor pressure of solution at that temperature Consider: X A = 1 X A = 0.9 X A = 0.5 {VapPress.WaterVsEthGlycol}

34 Solutions 2. Freezing Point Depression & 3. Boiling Point Elevation Nonvolatile solute- solvent interactions also cause solutions to have higher boiling points and lower freezing points than the pure solvent. f.pt. Pure solventf.pt. Solution b.pt. f.pt.

35 Solutions Freezing Point Depression The change in freezing point is proportional to the molality of the solution :  T f = K f  m Here K f is the molal freezing point depression constant of the solvent.  T f is subtracted from the normal freezing point of the solvent. {f.pt. Equil} {f.pt. Lower}

36 Solutions Boiling Point Elevation The change in boiling point is proportional to the molality of the solution:  T b = K b  m where K b is the molal boiling point elevation constant, a property of the solvent.  T b is added to the normal boiling point of the solvent.

37 Solutions Freezing Point Depression & Boiling Point Elevation Note that in both equations,  T does not depend on what the solute is, but only on how many particles are dissolved.  T f = K f  m  T b = K b  m

38 Solutions Osmosis The movement of water from an area of high concentration to lower concentration (diffusion) across a semipermeable membrane (SPM), until a homogeneous solution has been formed (equilibrium). The SPM allows smaller particles (water) to pass through, but blocks other larger particles. Diffusion of water across a SPM. Diffusion The movement of particles from an area of high concentration to lower concentration until a homogeneous solution has been formed.

39 Solutions Osmosis In osmosis, there is net movement of solvent from the area of higher solvent concentration (lower solute concentration) to the area of lower solvent concentration (higher solute concentration). {*OsmoPress} Solvent Solution

40 Solutions {*OsmoSemiPerMemb} Solution side (Low Conc. H2O) Solvent side (High Conc. H 2 O) SPM

41 Solutions Osmosis in Cells If the water concentration outside the cell is more than that inside the cell, the solution is hypotonic (low in solute). Water will flow into the cell, and hemolysis results. {EggOsmoPres} H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O High Water Low Water H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O (high solute) (low solute)

42 Solutions Osmosis in Blood Cells If the water concentration outside the cell is lower than that inside the cell, the solution is hypertonic (high in solute). Water will flow out of the cell, and crenation results. Isotonic: equal concentrations. H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O (salt water) (salt water) High Water (high solute) (low solute) H2OH2O H2OH2O H2OH2O H2OH2O

43 Solutions 3. Osmotic Pressure The pressure required to stop osmosis, known as osmotic pressure, , is nVnV  = ( ) RT where M is the molarity of the solution  V = n RT  = MRT

44 Solutions Reverse Osmosis The method of purifying liquid by pushing it through a semi-permeable membrane. Pressure is utilized to reverse the natural osmotic flow through a synthetic membrane so that pure water molecules pass through and impurities are flushed away. What exactly is Reverse Osmosis? Reverse Osmosis is the method of purifying liquid by pushing it through a semi- permeable membrane.Osmosis is the process by which water and nutrients are supplied to living cells. The natural flow of water is from a dilute to a concentrated solution across a cell wall. Cell walls are natural, selective semi- permeable membranes, which allow certain materials to pass through but reject others.In a reverse osmosis system, pressure is utilised to reverse the natural flow through a synthetic membrane so that pure water molecules pass through and impurities are flushed away. {RevOsmo} Membrane H2OH2OH2OH2OH2OH2O Contaminated water Reverse Osmosis What exactly is Reverse Osmosis? Reverse Osmosis is the method of purifying liquid by pushing it through a semi- permeable membrane.Osmosis is the process by which water and nutrients are supplied to living cells. The natural flow of water is from a dilute to a concentrated solution across a cell wall. Cell walls are natural, selective semi- permeable membranes, which allow certain materials to pass through but reject others.In a reverse osmosis system, pressure is utilised to reverse the natural flow through a synthetic membrane so that pure water molecules pass through and impurities are flushed away. {RevOsmo} Membrane H2OH2OH2OH2OH2OH2O Pure H2OH2O Contaminated water

45 Solutions Determining Molar Mass from Colligative Properties We can use the effects of a colligative property such as freezing point depression to determine the molar mass (MM) of a compound. A solution of an unknown nonvolatile electrolyte was prepared by dissolving 0.250g of the substance in 40.0 g of CCl 4. The b. pt. of the resultant solution was C higher than that of the pure solvent. What is MM of solute? The K b for CCl 4 is C/m.  T b = K b  m

46 Solutions Determining Molar Mass from Colligative Properties We can use the effects of a colligative property such as osmotic pressure to determine the molar mass of a compound.  = MRT The osmotic pressure of a protein solution was 25 0 C to be 1.54 torr. The solution contained 3.50 mg of protein dissolved in water to make 5.00 mL of solution. Determine the molar mass (MM) of the protein.

47 Solutions  = MRT  Vapor pressure lowering:  Boiling point elevation:  Freezing point depression:  Osmotic pressure:  T f = K f  m P A = X A  P  A Colligative Properties & Molar Mass =  P  A  T b = K b  m = K b  = K f  = RT

48 Solutions Colligative Properties of Electrolytes Since these properties depend on the number of particles dissolved, solutions of electrolytes (which dissociate in solution) should show greater changes than those of nonelectrolytes. You would expect a 1 M solution of CaCl 2 to show three times the change in freezing point that a 1 M solution of C 6 H 12 O 6, however ……………. CaCl 2 (s) Ca 2+ (aq) + 2Cl - (aq) H2OH2O C 6 H 12 O 6 (s) C 6 H 12 O 6 (aq) H2OH2O 1η1η 1 η molecules 1η1η 3 η ions Non-electrolyte: Electrolyte:

49 Solutions van’t Hoff Factor One mole of NaCl in water does not really give rise to two moles of ions. Some Na + and Cl − reassociate for a short time, so the true concentration of particles is somewhat less than two times the concentration of NaCl. Reassociation is more likely at higher concentration. Therefore, the number of particles present is concentration dependent.

50 Solutions The van’t Hoff Factor We modify the previous equations for Colligative Properties by multiplying them by the van’t Hoff factor, i Equations  Vapor pressure lowering:  Boiling point elevation:  Freezing point depression:  Osmotic pressure:  = i MRT  T b = i K b  m  T f = i K f  m P A = i X A P  A

51 Solutions Colloidal Dispersion homogeneous mixtures of particles larger than individual ions or molecules, but too small to be settled out by gravity.

52 Solutions Tyndall Effect The scattering of light by colloids.

53 Solutions Colloids in Biological Systems Some molecules have a polar, hydrophilic (water- loving) end and a nonpolar, hydrophobic (water- hating) end. Sodium stearate is one example of such a molecule. Non- Polar Tail Polar Head Soap Micelles in water solution H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O

54 Solutions Colloids in Biological Systems These molecules can aid in the emulsification of fats and oils in aqueous solutions. {Cotton Fabric Softener} {Micelle}

55 Solutions Suspension: heterogenousheterogenous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre.[1] The internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation, with the use of certain excipients or suspending agents.solidsedimentation[1]agitation

56 Solutions

57

58

59

60

61 2006 (A)

62 Solutions

63

64

65 2003 A

66 Solutions Na + (aq) + C 2 H 3 O 2 _ (aq) NaC 2 H 3 O 2(s) Energetics of Solutions Heats of Solution (  H soln ) crystallization Recyclable Hot Pack: Super Saturated Solution of Sodium Acetate heating {HotPack Na Acet} ∆H soln = - 67 kJ/n


Download ppt "Solutions Unit 12: Properties of Solutions Dr. Jorge L. Alonso Miami-Dade College – Kendall Campus Miami, FL Textbook Reference: Chapter # 14 Module #"

Similar presentations


Ads by Google