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Properties of Solutions Chapter 13 BLB 11 th

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Properties of Solutions. Chapter 13 BLB 11 th. Expectations:. g ↔ mol (using molar mass) g ↔ mL (using density) Other conversions: temp., pressure, etc. Solve for any variable in a formula. Distinguish between molecular and ionic compounds. - PowerPoint PPT Presentation

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Page 1: Properties of Solutions

Properties of SolutionsChapter 13 BLB 11th

Page 2: Properties of Solutions

Expectations: g ↔ mol (using molar mass) g ↔ mL (using density) Other conversions: temp., pressure, etc. Solve for any variable in a formula. Distinguish between molecular and ionic

compounds. Convert between different concentration

units. Describe the properties of solutions.

Page 3: Properties of Solutions

13.1 The Solution Process Solution – homogeneous mixture

Solute – present in smaller quantity Solvent – present in larger quantity

Intermolecular forces are rearranged when a solute and solvent are mixed.

Page 4: Properties of Solutions

Making a Solution1. Solute molecules separate (endothermic)2. Solvent molecules separate (endothermic)3. Formation of solute-solvent interactions

(exothermic)ΔHsoln = total energy

ΔHsoln – enthalpy change for the formation of a solution; exothermic – usually favorable; endothermic – usually unfavorable

Page 5: Properties of Solutions
Page 6: Properties of Solutions

Will a solution form? Solute-solvent interaction must be stronger or

comparable to the separation of solute and solvent particles.

Intermolecular forces play a key role. Entropy (disorder) is also a factor.

Disorder is favorable. (2nd law of thermodynamics) Solution formation increases entropy.

Dissolve vs. react (p. 533-4)

Page 7: Properties of Solutions

Entropy in Solution Formation

Ionic compoundvery ordered

As the ionic compound dissolves, itbecomes more disordered.

Page 8: Properties of Solutions

13.2 Saturated Solutions and Solubility Saturated solution – solution is in equilibrium

with undissolved solute.

Solute + solvent ⇌ solution

Unsaturated – less solute than saturated Supersaturated – more solute than saturated

dissolution

crystallization

Page 9: Properties of Solutions

A Saturated Solution

A dynamic equilibrium – ions continually exchange between the solid and solution form.

Page 10: Properties of Solutions

13.3 Factors Affecting Solubility1. Like dissolves like, i.e. same polarity.

Polar solutes are soluble in polar solvents. Nonpolar solutes are soluble in nonpolar solvents. If two liquids: miscible or immiscible

Examples:✔ water + alcohol, NaCl + water, hexane + pentane✘ water + hexane, NaCl + benzene, oil + water

Page 11: Properties of Solutions

Fat- and Water-Soluble Vitamins

Page 12: Properties of Solutions

13.3 Factors Affecting Solubility2. Pressure Effects (for gases in any liquid

solvent) Solubility increases as the partial pressure above the

solution increases. Henry’s Law: Sg = kPg

Sg – solubility of gask – Henry’s Law constant; conc./pressure unitsPg – partial pressure of gas above solution

Page 13: Properties of Solutions

The partial pressure of O2 in your lungs varies from 25 to 40 torr. What molarity of O2 can dissolve in water at each pressure? The Henry’s Law constant for O2 is 6.02 x 10-5 M/torr.

Page 14: Properties of Solutions

13.3 Factors Affecting Solubility3. Temperature Effects

For solids: Solubility ↑ as temperature ↑ - usually. If ΔHsoln > 0 (endothermic) If ΔHsoln < 0 (exothermic)

For gases: Solubility ↓ as temperature ↑ - always. Kinetic energy plays a primary role. Entropy is also a factor.

Page 15: Properties of Solutions

Ioniccompounds

Page 16: Properties of Solutions

Gases(In liquids)

Page 17: Properties of Solutions

13.4 Ways of Expressing Concentration Mass %, volume %, and ppm

610solutiongsolutegppm

100%solutionmLsolutemL%volume

100%solutiongsoluteg%mass

Page 18: Properties of Solutions

13.4 Ways of Expressing Concentration, cont. Mole fraction, molarity, and molality

solventkgsolutemol

solutionLsolutemolsolutionmolsolutemol

m

M

X

Page 19: Properties of Solutions

44. A solution contains 80.5 g ascorbic acid (C6H8O6) in 210 g water and has a density of 1.22 g/mL at 55°C.Calculate mass %, X, m, and M.

Page 20: Properties of Solutions

51. Commercial aqueous nitric acid has a density of 1.42 g/mL and is 16 M. Calculate mass % of HNO3.

Page 21: Properties of Solutions

43. A sulfuric acid solution containing 571.6 g of H2SO4 per liter of solution has a density of 1.329 g/cm3. Calculate the mass %, mole fraction, molality, and molarity.

Page 22: Properties of Solutions

Concentration Problems Practice! See Figure 13.19, p. 545, for conversion map. Several examples on pp. 544-6.

Page 23: Properties of Solutions

13.5 Colligative Properties The addition of a solute to a pure solvent:

1. Lowers the vapor pressure2. Lowers the freezing point3. Raises the boiling point4. Causes movement through a semipermeable

membrane (osmosis) Depends on the number of solute particles (moles),

not the identity; more particles the greater the effect Ionic compounds cause an even greater effect.

Page 24: Properties of Solutions
Page 25: Properties of Solutions

1. Lowering the vapor pressure Addition of solute blocks the solvent from

evaporation. More solute, less vapor, lower vapor pressure Raoult’s Law (for a nonvolatile solute):

PA = XAPA° PA – solvent v. p. over solution(PA < PA°) PA° – pure solvent v. p.

XA – mole fraction of solvent

Page 26: Properties of Solutions

1. Lowering the vapor pressure, cont. When a volatile solute is added, both the

solvent and solute contribute to the vapor pressure.

“Expanded” Raoult’s Law: Ptotal = PA + PB = XAPA° + XBPB°

If a solution obeys Raoult’s Law, it is an ideal solution.

Nonideal solutions have strong intermolecular interactions which lower the vapor pressure of the solution even further.

Page 27: Properties of Solutions

Vapor Pressure Lowering

Page 28: Properties of Solutions

62a. Calculate the vapor pressure above a solution of 32.5 g C3H8O3 (glycerin-nonvolatile) in 125 g water at 343 K. The vapor pressure of water at 343 K is 233.7 torr.

Page 29: Properties of Solutions

63. A solution is made from equal masses of water and ethanol (C2H5OH). Calculate the vapor pressure above the solution at 63.5°C. The vapor pressures of water and ethanol are 175 and 400. torr, respectively, at 63.5°C.

Page 30: Properties of Solutions

2. Boiling point elevation3. Freezing point depression

Since a solution has a lower vapor pressure: A higher temperature is needed to boil solution A lower temperature is needed to freeze solution.

To calculate effect:b.p. ↑ ΔTb = Kb·m solution − solventf.p. ↓ ΔTf = Kf·m solvent − solution ΔT – difference between boiling or freezing points of the pure

solvent and solution K – boiling or freezing pt. dep. constant (specific to solvent) m – molality

Page 31: Properties of Solutions

69a. Calculate the freezing and boiling points of a solution that is 0.40 m glucose in ethanol.For ethanol: f.p. -114.6°C, b.p. 78.4°C, Kf = 1.99 °C/m, Kb = 1.22 °C/m

Page 32: Properties of Solutions

72. Calculate the molar mass of lauryl alcohol when 5.00 g of lauryl alcohol is dissolved in 0.100 kg benzene (C6H6). The freezing point of the solution is 4.1°C. For benzene: f.p. 5.5°C, Kf = 5.12 °C/m

Page 33: Properties of Solutions

4. OsmosisOsmosis – movement of solvent molecules through

a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration

Driving force – to dilute the higher concentration Continues until:

Equilibrium is reached between two solutions, or External pressure prevents further movement.

Page 34: Properties of Solutions
Page 35: Properties of Solutions

Osmosis in red blood cells

Hypertonic solution Hypotonic solution

Page 36: Properties of Solutions

4. Osmosis, cont.Osmotic pressure

P = M R T P – osmotic pressure (atm)M – molarityR – 0.08206

L∙atom/mol∙KT – temperature (K)

Good technique for measuring molar mass of large molecules like proteins

Page 37: Properties of Solutions

4. Osmosis, cont. Applications:

Kidney dialysis Intercellular transport

Reverse osmosis – apply external pressure to reverse the flow of solvent molecules Water purification – alternative to salt ion exchange Desalination – purification of salt water

Page 38: Properties of Solutions

78. A dilute aqueous solution of an organic compound is formed by dissolving 2.35 g in water to form 0.250 L of solution. The resulting solution has an osmotic pressure of 0.605 atm at 25°C. Calculate the molar mass of the compound.

Page 39: Properties of Solutions

13.6 Colloids Colloid or colloidal dispersion

Intermediate between a solution and a suspension Dispersing medium – analogous to solvent Dispersing phase – analogous to solute; typically

large molecules with high molar masses Does not settle Tyndall effect – particles scatter light

Page 40: Properties of Solutions

Tyndall Effect

Page 41: Properties of Solutions

Types of Colloids

Page 42: Properties of Solutions

Surfactants Change the surface properties so that two

things that would not normally mix do Emulsifying agent Soap Detergent

Page 43: Properties of Solutions

Hydrophobic – water-fearing (nonpolar)Hydrophilic – water-loving (polar)

Page 44: Properties of Solutions

Action of soap on oil