Chapter 13 – Properties of Solutions

Jennie L. Borders

Section 13.1 – The Solution ProcessSection 13.1 – The Solution Process

• A solution is a homogeneous mixture.A solution is a homogeneous mixture.

• The solvent is present in the largest The solvent is present in the largest amount.amount.

• The solutes are the other components.The solutes are the other components.

• Aqueous solutions are have water as Aqueous solutions are have water as the solvent.the solvent.

• Solutions can be solids, liquids, or Solutions can be solids, liquids, or gases.gases.

SolutionsSolutions

• The ability of substances to form The ability of substances to form solutions depends on two factors:solutions depends on two factors:

1.1. The intermolecular forces involved.The intermolecular forces involved.

2.2. The tendency of the substance to spread The tendency of the substance to spread into larger volumes.into larger volumes.

Intermolecular ForcesIntermolecular Forces

• Ion-dipole forces are present when ionic Ion-dipole forces are present when ionic substance dissolve in water.substance dissolve in water.

• Dispersion forces are present when Dispersion forces are present when nonpolar substances form solutions.nonpolar substances form solutions.

• Solutions form when the attractive Solutions form when the attractive forces between the solute and solvent forces between the solute and solvent particles are comparable to the forces particles are comparable to the forces that exist between 2 solute particles or that exist between 2 solute particles or 2 solvent particles.2 solvent particles.

Solvation and HydrationSolvation and Hydration

• Solvation is the interaction between the Solvation is the interaction between the solute and solvent particles.solute and solvent particles.

• Hydration is the interaction between the Hydration is the interaction between the solute and solvent particles when the solute and solvent particles when the solvent is water.solvent is water.

Energy ChangesEnergy ChangesHHsolnsoln = = HH11 + + HH22 + + HH33

HHsolnsoln is the energy change when the is the energy change when the

solution forms.solution forms. HH11 is the energy is the energy requiredrequired to separate the to separate the

solute particles (endothermic).solute particles (endothermic). HH22 is the energy is the energy requiredrequired to separate the to separate the

solvent particles (endothermic).solvent particles (endothermic). HH33 is the energy is the energy releasedreleased when the solute when the solute

and solvent particles attract (exothermic).and solvent particles attract (exothermic).

Energy Changes

Will a solution form?Will a solution form?

• Processes that are exothermic tend to Processes that are exothermic tend to be spontaneous, but endothermic be spontaneous, but endothermic processes still occur. processes still occur.

Ex: ammonium nitrate spontaneously Ex: ammonium nitrate spontaneously dissolves in water even though dissolves in water even though HHsolnsoln = =

26.4 kJ/mol26.4 kJ/mol

EntropyEntropy• Spontaneous processes involve two Spontaneous processes involve two

factors:factors:

1. energy (exothermic)1. energy (exothermic)

2. tendency to spread out 2. tendency to spread out

• Entropy is the degree of randomness or Entropy is the degree of randomness or disorder of a system.disorder of a system.

• Processes in which the entropy Processes in which the entropy (randomness) of the components (randomness) of the components increases tend to be spontaneous.increases tend to be spontaneous.

SolutionsSolutions

• The formation of solutions involves The formation of solutions involves enthalpy (energy change) and entropy enthalpy (energy change) and entropy (randomness).(randomness).

Sample Exercise 13.1Sample Exercise 13.1

• The picture below shows the following The picture below shows the following reaction:reaction:

NaNa22SOSO4(s)4(s) + 10H + 10H22OO(g)(g) Na Na22SOSO44..10H10H22OO(s)(s)

Essentially all of the water vapor in the Essentially all of the water vapor in the closed container is consumed in this closed container is consumed in this

reaction.reaction.

Sample Exercise 13.1 con’tSample Exercise 13.1 con’t

• If we consider our system to consist If we consider our system to consist initially of Nainitially of Na22SOSO4(s) 4(s) and 10Hand 10H22OO(g) (g)

a. does the system become more or a. does the system become more or less ordered in the process?less ordered in the process?

b. does the entropy of the system b. does the entropy of the system increase or decrease?increase or decrease?

Practice ExercisePractice Exercise

• Does the entropy of the system Does the entropy of the system increase or decrease when the increase or decrease when the stopcock is opened to allow mixing of stopcock is opened to allow mixing of the two gases in the apparatus?the two gases in the apparatus?

Section 13.2 – Saturated Section 13.2 – Saturated Solutions and SolubilitySolutions and Solubility

• DissolvingDissolving and and crystallizationcrystallization are are opposite processes.opposite processes.

Solute + solvent Solute + solvent solution solution

SolubilitySolubility• The maximum amount of solute that will The maximum amount of solute that will

dissolve in a given amount of solvent at dissolve in a given amount of solvent at a specified temperature is the solubility.a specified temperature is the solubility.

UnsaturatedUnsaturated

• An unsaturated solution contains less An unsaturated solution contains less than the maximum amount of solute at a than the maximum amount of solute at a given temperature.given temperature.

• If more solute is added, then itIf more solute is added, then it

will dissolve.will dissolve.

SaturatedSaturated

• A saturated solution contains the A saturated solution contains the maximum amount of solute at a given maximum amount of solute at a given temperature.temperature.

• If more solute is added, thenIf more solute is added, then

it will not dissolve and it willit will not dissolve and it will

settle at the bottom.settle at the bottom.

SupersaturatedSupersaturated

• A supersaturated solution contains A supersaturated solution contains more than the maximum amount of more than the maximum amount of solute at a given temperature.solute at a given temperature.

• A supersaturated solution is made by A supersaturated solution is made by heating the solvent to a higher heating the solvent to a higher temperature so that more solute can be temperature so that more solute can be dissolved.dissolved.

• The solution is then carefully cooled so The solution is then carefully cooled so that crystallization does not occur.that crystallization does not occur.

SupersaturatedSupersaturated

• If more solute is added, then rapid If more solute is added, then rapid crystallization occurs.crystallization occurs.

• Supersaturated solutions areSupersaturated solutions are

extremely unstable.extremely unstable.

Section 13.3 – Factors Affecting Section 13.3 – Factors Affecting SolubilitySolubility

• The stronger the attractions between The stronger the attractions between the solute and solvent molecules, the the solute and solvent molecules, the greater the solubility.greater the solubility.

• Polar solvents tend to dissolve polar or Polar solvents tend to dissolve polar or ionic solutes.ionic solutes.

• Nonpolar solvents tend to dissolve Nonpolar solvents tend to dissolve nonpolar solutes.nonpolar solutes.

• ““Like dissolves like.”Like dissolves like.”

Miscible vs. ImmiscibleMiscible vs. Immiscible

• Liquids that are miscible will dissolve Liquids that are miscible will dissolve one another. Ex: water and rubbing one another. Ex: water and rubbing alcoholalcohol

• Liquids that are immiscible will not Liquids that are immiscible will not dissolve one another. Ex: water and oildissolve one another. Ex: water and oil

Hydrocarbon MoleculesHydrocarbon Molecules• C-H bonds are considered nonpolar due C-H bonds are considered nonpolar due

to the small difference in to the small difference in electronegativity.electronegativity.

• Hydrocarbons tend to be insoluble in Hydrocarbons tend to be insoluble in polar solvents.polar solvents.

• One way to increase the solubility is to One way to increase the solubility is to increase the number of polar groups. increase the number of polar groups. Ex: an alcohol group –OH.Ex: an alcohol group –OH.

AlcoholsAlcohols

• As the carbon chain of an alcohol As the carbon chain of an alcohol increases, the solubility decreases due increases, the solubility decreases due to the increased London dispersion to the increased London dispersion forces. The molecule starts to act more forces. The molecule starts to act more nonpolar.nonpolar.

Network SolidsNetwork Solids• Network solids are not soluble in polar Network solids are not soluble in polar

or nonpolar substances due to the or nonpolar substances due to the strong bonding forces within the solid.strong bonding forces within the solid.

Sample Exercise 13.2Sample Exercise 13.2

• Predict whether each of the following Predict whether each of the following substances is more likely to dissolve in substances is more likely to dissolve in the nonpolar solvent carbon the nonpolar solvent carbon tetrachloride or water: Ctetrachloride or water: C77HH1616, Na, Na22SOSO44, ,

HCl, and IHCl, and I22..

Practice ExercisePractice Exercise• Arrange the following substances in Arrange the following substances in

order of increasing solubility in water:order of increasing solubility in water:

PressurePressure• The solubilities of liquids and solids are The solubilities of liquids and solids are

not affected by pressure, but the not affected by pressure, but the solubility of a gas is affected.solubility of a gas is affected.

• The solubility of a gas increases when The solubility of a gas increases when pressure is increased.pressure is increased.

Henry’s LawHenry’s Law• Henry’s Law shows the relationship Henry’s Law shows the relationship

between pressure and solubility of a gas:between pressure and solubility of a gas:

SSgg = kP = kPgg

SSgg = solubility of a gas (M = molarity) = solubility of a gas (M = molarity)

k = Henry’s law constant (different for each k = Henry’s law constant (different for each solute-solvent pair and changes with solute-solvent pair and changes with temperature) (mol/Ltemperature) (mol/L..atm)atm)

PPgg = partial pressure of the gas (atm) = partial pressure of the gas (atm)

Sample Exercise 13.3Sample Exercise 13.3

• Calculate the concentration of COCalculate the concentration of CO22 in a in a

soft drink that is bottled with a partial soft drink that is bottled with a partial pressure of COpressure of CO22 of 4.0 atm over the of 4.0 atm over the

liquid at 25liquid at 25ooC. The Henry’s law constant C. The Henry’s law constant for COfor CO22 in water at this temperature is in water at this temperature is

3.1 x 103.1 x 10-2-2 mol/L mol/L..atm.atm.

Practice ExercisePractice Exercise

• Calculate the concentration of COCalculate the concentration of CO22 in a in a

soft drink after the bottle is opened and soft drink after the bottle is opened and equilibrates at 25equilibrates at 25ooC under a COC under a CO22 partial partial

pressure of 3.0 x 10pressure of 3.0 x 10-4-4 atm. atm.

TemperatureTemperature• The solubility of most solids increases The solubility of most solids increases

as temperature increases.as temperature increases.

• The solubility of most gases decreases The solubility of most gases decreases with increasing temperature.with increasing temperature.

Section 13.4 – Ways of Section 13.4 – Ways of Expressing ConcentrationExpressing Concentration

• We do not need to cover parts per We do not need to cover parts per million (ppm), parts per billion (ppb), million (ppm), parts per billion (ppb), mass percent, molality, or normality.mass percent, molality, or normality.

Mole Fraction and MolarityMole Fraction and Molarity

• Mole Fraction = Mole Fraction = mole of componentmole of component

total molestotal moles

• Molarity = Molarity = moles of solute moles of solute

liters of solutionliters of solution

MolarityMolarity

• The molarity of a solution does change The molarity of a solution does change with temperature because the with temperature because the contraction or expansion of the solution contraction or expansion of the solution changes the volume.changes the volume.

Sample Exercise 13.6Sample Exercise 13.6

• An aqueous solution of hydrochloric An aqueous solution of hydrochloric acid contains 36% HCl by mass. acid contains 36% HCl by mass. Calculate the mole fraction of HCl in the Calculate the mole fraction of HCl in the solution. solution.

Practice ExercisePractice Exercise

• A commercial bleach solution contains A commercial bleach solution contains 3.62 mass % NaOCl in water. Calculate 3.62 mass % NaOCl in water. Calculate the mole fraction of NaOCl in the the mole fraction of NaOCl in the solution.solution.

Section 13.5 – Colligative Section 13.5 – Colligative PropertiesProperties

• Colligative properties are properties of a Colligative properties are properties of a solvent that change when solute solvent that change when solute particles are added.particles are added.

• Colligative properties are only based on Colligative properties are only based on the number of solute particles, not the the number of solute particles, not the identity of the solute.identity of the solute.

Vapor PressureVapor Pressure

• The vapor pressure of a substance The vapor pressure of a substance lowers when solute particles are added lowers when solute particles are added because the solvent particles are because the solvent particles are attracted to the solute particles.attracted to the solute particles.

Boiling PointBoiling Point

• The boiling point of a solvent elevates The boiling point of a solvent elevates when solute particles are added when solute particles are added because the solvent particles are because the solvent particles are attracted to the solute particles.attracted to the solute particles.

Freezing PointFreezing Point• The freezing point of a solvent The freezing point of a solvent

depresses (lowers) when solute depresses (lowers) when solute particles are added because the solvent particles are added because the solvent particles are attracted to the solute particles are attracted to the solute particles.particles.

OsmosisOsmosis• Materials that only allow some Materials that only allow some

molecules to pass through are called molecules to pass through are called semipermeable.semipermeable.

• For example, a membrane may allow For example, a membrane may allow small water molecules to pass through small water molecules to pass through but not larger solute particles.but not larger solute particles.

• Osmosis is the net movement of solvent Osmosis is the net movement of solvent toward the solution with thetoward the solution with the

higher solute concentration.higher solute concentration.

Colligative PropertiesColligative Properties

• Colligative properties are considered Colligative properties are considered prior knowledge and should not be prior knowledge and should not be directly assessed on the AP exam, so I directly assessed on the AP exam, so I have just provided a brief overview to have just provided a brief overview to make sure that you are familiar with make sure that you are familiar with them.them.

Section 13.6 - ColloidsSection 13.6 - Colloids

• Solutions contain very small solute Solutions contain very small solute particles.particles.

• Colloids contain intermediate (medium-Colloids contain intermediate (medium-sized) solute particles. Colloid particles sized) solute particles. Colloid particles are between 5 to 1000 nm.are between 5 to 1000 nm.

• Suspension contain large solute Suspension contain large solute particles that settle over time.particles that settle over time.

ColloidsColloids

• Colloids particles are small enough to Colloids particles are small enough to seem uniform, but they are large seem uniform, but they are large enough to scatter light.enough to scatter light.

• The scattering of light by colloid The scattering of light by colloid particles is called the Tyndall effect.particles is called the Tyndall effect.

Hydrophilic and HydrophobicHydrophilic and Hydrophobic

• Hydrophilic colloids are “water loving.”Hydrophilic colloids are “water loving.”

• Hydrophobic colloids are “water Hydrophobic colloids are “water fearing.”fearing.”

Adsorption vs. AbsorptionAdsorption vs. Absorption

• Adsorption means to adhere to a Adsorption means to adhere to a surface.surface.

• Absorption means to pass into the Absorption means to pass into the interior.interior.

Biology … INFERIOR!Biology … INFERIOR!

• In the body, hydrophobic colloids can In the body, hydrophobic colloids can mix with water by adsorbing ions onto mix with water by adsorbing ions onto the surface.the surface.

Removal of Colloid ParticlesRemoval of Colloid Particles• Colloid particles are too small to be Colloid particles are too small to be

removed by filtration.removed by filtration.

• Coagulation is a process of enlarging Coagulation is a process of enlarging the colloid particles so that they can be the colloid particles so that they can be removed.removed.

• Heating a colloid or adding electrolytes Heating a colloid or adding electrolytes can bring about coagulation.can bring about coagulation.

CoagulationCoagulation

Sample Integrative ExerciseSample Integrative Exercise

• A 0.100L solution is made by dissolving A 0.100L solution is made by dissolving 0.441g of CaCl0.441g of CaCl2(s)2(s) in water. The enthalpy in water. The enthalpy

of solution for CaClof solution for CaCl22 is is H = -81.3 H = -81.3

kJ/mol. If the final temperature of the kJ/mol. If the final temperature of the solution is 27.0solution is 27.0ooC, what was the initial C, what was the initial temperature? (Assume that the density temperature? (Assume that the density of the solution is 1.00 g/mL, that its of the solution is 1.00 g/mL, that its specific heat is 4.18 J/gspecific heat is 4.18 J/g..K, and that the K, and that the solution loses no heat to its solution loses no heat to its surroundings.)surroundings.)