Chapter 15Chapter 15

Solution Definitions Solution Definitions to Know & Useto Know & Use

Solution – Solution – homogenous mixture of two or homogenous mixture of two or more substances in a single physical more substances in a single physical state.state.

SoluteSolute – the substance – the substance beingbeing dissolveddissolved.. SolventSolvent – the – the principalprincipal componentcomponent that that

dissolves another component of a dissolves another component of a solution.solution.

SolubilitySolubility – a – a quantifiablequantifiable measuremeasure of the of the degree to which a substance dissolves in degree to which a substance dissolves in another substance.another substance.

SolubleSoluble – a substance that can be – a substance that can be dissolved in another substance.dissolved in another substance.

InsolubleInsoluble – a substance that cannot be – a substance that cannot be dissolved in another substance.dissolved in another substance.

Chapter 15 “Solutions”Chapter 15 “Solutions” What are solutions?What are solutions?

HomogeneousHomogeneous mixturesmixtures of two or more of two or more substances in a single physical state.substances in a single physical state.

A solution consists of a A solution consists of a solutesolute dissolved in a dissolved in a solventsolvent..

Many examples exist. Many examples exist. What are the What are the intrinsicintrinsic properties of properties of

solutions?solutions?1.1. Contain very small particles Contain very small particles

(atoms, ions, molecules)(atoms, ions, molecules)2.2. Homogeneous throughout. (Particles are Homogeneous throughout. (Particles are

evenly distributed on a molecular level).evenly distributed on a molecular level).3.3. Particles do not separate with time under Particles do not separate with time under

constant conditions.constant conditions.4.4. Diverse physical states and chemical Diverse physical states and chemical

compositions.compositions.

Types of SolutionsTypes of Solutions Solid SolutionsSolid Solutions

Alloys (14 carat gold, stainless steel, Alloys (14 carat gold, stainless steel, brass)brass)

Gaseous SolutionsGaseous Solutions Air, scuba diving gases, vehicle Air, scuba diving gases, vehicle

exhaustexhaust Liquid SolutionsLiquid Solutions

Vinegar, antifreeze, Vinegar, antifreeze, Aqueous SolutionsAqueous Solutions

Solutions with water as solvent.Solutions with water as solvent. Seawater, soft drinksSeawater, soft drinks

15-2 Concentration of 15-2 Concentration of SolutionsSolutions

ConcentrationConcentration – – the amount of solute the amount of solute dissolved per unit of solvent.dissolved per unit of solvent.

There are many ways to describe There are many ways to describe concentration, but they are either concentration, but they are either qualitativequalitative or or quantitativequantitative..

QualitativeQualitative – a representation of the – a representation of the general nature of a solution.general nature of a solution.

QuantitativeQuantitative – a measure of the amount of – a measure of the amount of a solute dissolved in the solution. a solute dissolved in the solution.

Qualitative Descriptions Qualitative Descriptions of Solutionsof Solutions

DiluteDilute – a solution containing very little – a solution containing very little solute.solute.

ConcentratedConcentrated – a solution containing a large – a solution containing a large amount of solute.amount of solute.

Qualitative Descriptions of Qualitative Descriptions of SolutionsSolutions

SaturatedSaturated – a solution containing the – a solution containing the maximummaximum amountamount of solute that can be of solute that can be dissolved dissolved at the current at the current temperature/pressuretemperature/pressure..

UnsaturatedUnsaturated – a solution containing – a solution containing less than less than the maximum amountthe maximum amount of solute that can be of solute that can be dissolved dissolved at the current at the current temperature/pressuretemperature/pressure..

SupersaturatedSupersaturated – an – an unstableunstable condition in condition in which a solution contains which a solution contains more than the more than the maximum amountmaximum amount of solute that can normally of solute that can normally be dissolved be dissolved at the current at the current temperature/pressuretemperature/pressure..

Solution StabilitySolution Stability

Recall that a Recall that a saturatedsaturated solution contains the solution contains the maximummaximum amount of solute that can be dissolved at amount of solute that can be dissolved at given conditions.given conditions.

In a saturated solution, the rate of solute entering In a saturated solution, the rate of solute entering into solution precisely balances the rate at which into solution precisely balances the rate at which solute comes out of solution (forming a solute comes out of solution (forming a solidsolid precipitateprecipitate).).

The saturated solution is The saturated solution is stablestable and said to be in and said to be in dynamic equilibriumdynamic equilibrium..

Solution StabilitySolution Stability

In an In an unsaturatedunsaturated solution more solute can dissolve, solution more solute can dissolve, so it is not yet at equilibrium.so it is not yet at equilibrium.

In a In a supersaturatedsupersaturated solution more than the maximum solution more than the maximum amount of solute that can normally be dissolved at amount of solute that can normally be dissolved at the current conditions is present. This is an the current conditions is present. This is an unstable situation that is resolved by precipitating unstable situation that is resolved by precipitating solute (solid). The end result is an equilibrium solute (solid). The end result is an equilibrium condition.condition.

Saturation:Saturation:

Quantitative Descriptions of Quantitative Descriptions of SolutionsSolutions

Quantitative methods are much more useful Quantitative methods are much more useful than qualitative descriptions because they than qualitative descriptions because they specify the specify the amountsamounts of components in of components in solutions.solutions.

The most common The most common quantitativequantitative descriptions descriptions include:include: Molarity, Molarity, M = moles solute/L of solutionM = moles solute/L of solution

Molality, Molality, m = moles of solute/kg of solventm = moles of solute/kg of solvent

Molarity, Molarity, MM Molarity (Molarity (MM)) – moles of solute per – moles of solute per literliter of of

solutionsolution.. MM = moles/L = moles/L What is the molarity of a solution made from 145 g What is the molarity of a solution made from 145 g

of NaCl in 2.75 L of solution?of NaCl in 2.75 L of solution?

Vinegar is a solution of acetic acid. What is Vinegar is a solution of acetic acid. What is the molarity of the solution produced when the molarity of the solution produced when 125g of acetic acid (C125g of acetic acid (C22HH44OO22) is dissolved in ) is dissolved in

sufficient water to prepare 1.50L of solution?sufficient water to prepare 1.50L of solution?

Molality, Molality, mm Molality (Molality (mm)) – moles of solute per – moles of solute per kilogramkilogram of of solventsolvent..

m m = moles/kg= moles/kg

What is the molality of a solution made from 20.4 g What is the molality of a solution made from 20.4 g KBr in 195 g of water?KBr in 195 g of water?

What is the molality of a solution containing 125g of What is the molality of a solution containing 125g of iodine (Iiodine (I22) and 750.g of carbon tetrachloride (CCl4)?) and 750.g of carbon tetrachloride (CCl4)?

Mole Fraction, Mole Fraction, xxsolutesolute Mole FractionMole Fraction – moles of component per – moles of component per totaltotal moles of moles of

solution.solution.

XXsolutesolute = = moles solutemoles solute total molestotal moles

ExampleExample: What is the mole fraction of sulfur dioxide in : What is the mole fraction of sulfur dioxide in an industrial exhaust gas containing 128.0 g of SOan industrial exhaust gas containing 128.0 g of SO22 dissolved in every 1500. g of COdissolved in every 1500. g of CO22??

AnswerAnswer::

XXSO2SO2 = (mole fraction SO = (mole fraction SO22)/(total moles of solution))/(total moles of solution)

Moles SOMoles SO22 = 128.0g • (1 mol SO = 128.0g • (1 mol SO22 /64.04g SO /64.04g SO22) = 1.999 mol SO) = 1.999 mol SO22

Moles COMoles CO22 = 1500.g CO = 1500.g CO22 • [1 mol CO • [1 mol CO22/44.01g CO/44.01g CO22] = 34.08 mol CO] = 34.08 mol CO22

XXSO2SO2 = = 1.999 mol SO1.999 mol SO22 ___________ ___________ = = 1.9991.999 = 0.05540= 0.05540

1.999 mol SO1.999 mol SO22 + 34.08 mol CO + 34.08 mol CO22 36.0836.08

Molarity and Dilution FactorsMolarity and Dilution Factors When diluting a solution into a When diluting a solution into a lessless concentrated one, concentrated one, the total the total

number of moles of solute does not change.number of moles of solute does not change. (The compound didn’t go anywhere; it is still in the container!)(The compound didn’t go anywhere; it is still in the container!)

Because Because MolarityMolarity = moles/volume, = moles/volume, the moles = the moles = MolarityMolarity * Volume, or * Volume, or MM V. V. Therefore we may write the following for the Therefore we may write the following for the eacheach of the two solutions: of the two solutions:

molesmoles11 = = MM11VV11 and moles and moles22 = = MM22VV22

Since there are the Since there are the same number of molessame number of moles in the first solution as in in the first solution as in the second, we may let molesthe second, we may let moles11 = moles = moles22, or also, or also

MMccVVcc = = MMddVVdd

Can use this simple equation to calculate the new molarity.Can use this simple equation to calculate the new molarity.

More Solution Definitions to More Solution Definitions to KnowKnow

MiscibleMiscible – liquids that may be mixed together in – liquids that may be mixed together in anyany amount.amount.

Oil and gasoline.Oil and gasoline. ImmiscibleImmiscible – liquids that cannot be mixed.– liquids that cannot be mixed.

Oil and water.Oil and water. Aqueous SolutionAqueous Solution – liquid solutions for which the – liquid solutions for which the

solvent is solvent is waterwater.. Acetic acid and water (vinegar).Acetic acid and water (vinegar).

ElectrolyteElectrolyte – a substance that – a substance that forms ionsforms ions in solution, in solution, enabling the solution to conduct electricity.enabling the solution to conduct electricity.

NaCl in sea water, Gatorade.NaCl in sea water, Gatorade. Non-electrolyteNon-electrolyte – a substance that – a substance that does not form ionsdoes not form ions

in solution, thus giving a non-conducting solution.in solution, thus giving a non-conducting solution. Sugar in tea.Sugar in tea.

15-3 Formation of Solutions15-3 Formation of Solutions DissolutionDissolution - the complex interaction of two or more separate - the complex interaction of two or more separate

substances (the solute and the solvent) to form a single system (the substances (the solute and the solvent) to form a single system (the solution).solution).

SolvationSolvation – the process whereby solvent particles pull the solute – the process whereby solvent particles pull the solute particles into solution and surround them; the interaction between particles into solution and surround them; the interaction between solute and solvent particles to form a solution.solute and solvent particles to form a solution.

HydrationHydration - the process whereby - the process whereby waterwater particles pull the solute particles pull the solute particles into solution and surround them to form a solution.particles into solution and surround them to form a solution.

SolubilitySolubility – a – a quantifiablequantifiable measuremeasure of the degree to which a of the degree to which a substance dissolves in another substance;substance dissolves in another substance; it is it is the the amountamount of a of a solute that will dissolve in a specific solvent under given conditions. solute that will dissolve in a specific solvent under given conditions. Expressed in gram of solute per 100 grams of solvent.Expressed in gram of solute per 100 grams of solvent.

Saturation:Saturation:

Factors Affecting SolubilityFactors Affecting Solubility1.1. Nature of Solute and SolventNature of Solute and Solvent

Similar substances dissolve in one another. Similar substances dissolve in one another. (“Likes (“Likes dissolve likes.”)dissolve likes.”)

PolarPolar substances dissolve in substances dissolve in polarpolar substances substances• Water dissolves sugar & salt.Water dissolves sugar & salt.• Water dissolves rubbing alcohol.Water dissolves rubbing alcohol.

NonpolarNonpolar substances dissolve in substances dissolve in nonpolarnonpolar substances.substances.

• Gasoline dissolves oil.Gasoline dissolves oil.• Dry cleaning fluids dissolve grease and oils.Dry cleaning fluids dissolve grease and oils.

2.2. Temperature – see next slidesTemperature – see next slides3.3. PressurePressure

Gas solubility increases with pressure. Gas solubility increases with pressure.

Solubility and TemperatureSolubility and Temperature

Solubility and TemperatureSolubility and Temperature

http://www.elmhurst.edu/~chm/vchembook/174temppres.html

Solubility of Solubility of salts:salts:

Solubility of gases:Solubility of gases:

TemperatureTemperatureSolubility of solids and liquids Solubility of solids and liquids generallygenerally

increases with temperature.increases with temperature.Solubility of gases decreases with Solubility of gases decreases with

temperature.temperature.

Energy Changes and the Energy Changes and the Formation of SolutionsFormation of Solutions

Solvation/Hydration may be Solvation/Hydration may be

exothermicexothermic or or endothermicendothermic..

ΔΔH H depends on the depends on the balancebalance of energy of energy releasedreleased by the by the attraction of solute particles to the solvent versus the attraction of solute particles to the solvent versus the energy energy consumedconsumed in breaking the attractions of in breaking the attractions of solute particles for each other (crystal lattice energy).solute particles for each other (crystal lattice energy).

Dissolving CaClDissolving CaCl22 is very exothermic, but an ammonium is very exothermic, but an ammonium

nitrate ‘cold pack’ works because the solvation is nitrate ‘cold pack’ works because the solvation is endothermic. endothermic.

Factors That Affect Factors That Affect Dissolution RatesDissolution Rates

1.1. Surface areaSurface area Increasing surface area (making smaller particles) Increasing surface area (making smaller particles)

increases the rate of dissolution. increases the rate of dissolution.

2.2. StirringStirring Stirring the solution increases the rate of Stirring the solution increases the rate of

dissolution. dissolution.

3.3. TemperatureTemperature Increasing the temperature increases the rate of Increasing the temperature increases the rate of

dissolution. dissolution.

15-4 Colligative Properties15-4 Colligative Properties

These are properties that depend on These are properties that depend on solution solution concentrationconcentration rather than the nature rather than the nature or type of solute. or type of solute.

They are dependent on molality They are dependent on molality (mol(molsolutesolute/kg/kgsolventsolvent))

Examples include…Examples include… Vapor Pressure ReductionVapor Pressure Reduction Boiling Point ElevationBoiling Point Elevation Freezing Point DepressionFreezing Point Depression

Vapor Pressure ReductionVapor Pressure Reduction Raoult’s LawRaoult’s Law – the magnitude of the vapor pressure reduction is proportional to – the magnitude of the vapor pressure reduction is proportional to

the solute concentration, regardless of the solute.the solute concentration, regardless of the solute.

Why? Nonvolatile solute molecules interfere with the solvent molecules, Why? Nonvolatile solute molecules interfere with the solvent molecules, preventing them from leaving the surface of the solution, and thus preventing them from leaving the surface of the solution, and thus decreasingdecreasing the vapor pressure. the vapor pressure.

(Fig. 15-22, p 520)(Fig. 15-22, p 520)

This results in an This results in an increase in the boiling pointincrease in the boiling point of the solvent, and a of the solvent, and a decrease in its freezing pointdecrease in its freezing point..

Boiling point elevationBoiling point elevationFreezing point depressionFreezing point depression

Applications? Applications?

““Freezing Point Depression”Freezing Point Depression” This is the ability of a dissolved This is the ability of a dissolved

solute to solute to lowerlower the freezing point of the freezing point of a solution.a solution. Example: Antifreeze is added to a car’s Example: Antifreeze is added to a car’s

coolant system to prevent freezing of coolant system to prevent freezing of the water in winter.the water in winter.

Decrease of freezing point is directly Decrease of freezing point is directly proportional to the molality (proportional to the molality (mm) of ) of the solute.the solute.

Calculated from Calculated from ΔΔTTff = = KKffmm……where where ΔΔTTff is the temperature is the temperature

depression, m is molality and Kdepression, m is molality and Kff is the is the freezing point depression constant.freezing point depression constant.

““Boiling Point Elevation”Boiling Point Elevation” This is the ability of a dissolved solute to This is the ability of a dissolved solute to raiseraise

the boiling point of a solution.the boiling point of a solution. Example: The antifreeze added to a car’s coolant Example: The antifreeze added to a car’s coolant

system also prevents overheating in summer!system also prevents overheating in summer!

Increase of boiling point is also directly Increase of boiling point is also directly proportional to the molality (proportional to the molality (mm) of the solute.) of the solute.

Calculated from Calculated from ΔΔTTbb = = KKbbmm

……where where ΔΔTTbb is the temperature depression, m is is the temperature depression, m is

molality and Kmolality and Kbb is the freezing point depression is the freezing point depression

constant.constant.

Post Lab QuestionsPost Lab Questions 1. Which compound types (ionic or covalent)

produce more particles when dissolved in water and why? Remember this is related to molality.

 2. Which type of compound (ionic or covalent) will have a greater effect on the colligative properties of a solution? Explain.   

Determining Molar MassDetermining Molar Mass A solution containing 16.9g of a nonvolatile molecular A solution containing 16.9g of a nonvolatile molecular

compound in 250g of water has a freezing point of -compound in 250g of water has a freezing point of -0.744 °C. What is the molar mass of the compound?0.744 °C. What is the molar mass of the compound?

Solution:Solution: First find the molality from First find the molality from ΔΔTTff = K = Kffm.m.

0.744 °C = (1.86 °C/0.744 °C = (1.86 °C/m)m) x x m,m,

so the molality = 0.400 so the molality = 0.400 molalmolal But But molality molality = moles/kg, so = moles/kg, so

0.400 m = ??? moles/0.250 kg, 0.400 m = ??? moles/0.250 kg,

from which ??? moles = 0.100 molefrom which ??? moles = 0.100 mole

-Since 0.100 mole = 16.9g of solute, 1.00 mole of solute = -Since 0.100 mole = 16.9g of solute, 1.00 mole of solute = 169 g, giving a molar mass of 169 g/mol.169 g, giving a molar mass of 169 g/mol.