Properties of SolutionsProperties of Solutions

Learning objectivesLearning objectives Define terms solute, solvent and solutionDefine terms solute, solvent and solution Distinguish between solutions and heterogeneous Distinguish between solutions and heterogeneous

mixturesmixtures Distinguish among non-, weak and strong electrolytesDistinguish among non-, weak and strong electrolytes Describe factors that affect solubilityDescribe factors that affect solubility Describe Henry’s law and its application to explain Describe Henry’s law and its application to explain

common phenomena involving gasescommon phenomena involving gases Perform calculations of solution concentration using Perform calculations of solution concentration using

various definitionsvarious definitions Use molarity in stoichiometry calculationsUse molarity in stoichiometry calculations Describe basis of Raoult’s law and colligative propertiesDescribe basis of Raoult’s law and colligative properties Calculate solute concentrations in colligative property Calculate solute concentrations in colligative property

contextcontext Explain basis of osmotic pressureExplain basis of osmotic pressure

Definitions of a solutionDefinitions of a solution

A homogeneous mixture of two or more A homogeneous mixture of two or more substancessubstances

Solute is the component that is dispersed in Solute is the component that is dispersed in the solvent – usually the minority the solvent – usually the minority componentcomponent

Solvent is the dispersing component – Solvent is the dispersing component – usually the majority componentusually the majority component Sometimes definitions can become blurred: water Sometimes definitions can become blurred: water

(solvent) dissolves much greater than its own mass of (solvent) dissolves much greater than its own mass of sugar (solute)sugar (solute)

Formation of a solutionFormation of a solution

Crystals are held together by strong ionic Crystals are held together by strong ionic bondsbonds

Polar water molecules exert attractive Polar water molecules exert attractive forces on ionsforces on ions

HydrationHydration of the ions by water molecules of the ions by water molecules overcomes lattice energyovercomes lattice energy

Crystal lattice dispersesCrystal lattice disperses

Like dissolves likeLike dissolves like

All gases mix with each because there are All gases mix with each because there are no intermolecular forcesno intermolecular forces

Solids and liquids mix if intermolecular Solids and liquids mix if intermolecular forces between unlike substances forces between unlike substances (adhesive forces) are similar to forces (adhesive forces) are similar to forces between like substances (cohesive forces)between like substances (cohesive forces)

ElectrolytesElectrolytes Electrolytes are substances that dissociate Electrolytes are substances that dissociate

into ions in solution – ionic compounds into ions in solution – ionic compounds (sodium chloride)(sodium chloride) Strong electrolytes are completely ionizedStrong electrolytes are completely ionized

Weak electrolytes are partly ionizedWeak electrolytes are partly ionized

Non-electrolytes are those substances that Non-electrolytes are those substances that

produce produce nono ions (sugar) ions (sugar)

2( ) ( ) ( )H ONaCl s Na aq Cl aq

2( ) ( ) ( ) ( )H OHF aq HF aq H aq F aq

Colloids and solutionsColloids and solutions

Both appear clear and uniformBoth appear clear and uniform Solution is homogeneous; colloid is Solution is homogeneous; colloid is

heterogeneousheterogeneous Colloid contains particles suspended in the Colloid contains particles suspended in the

liquidliquid• 1 – 200 nm diameter1 – 200 nm diameter

Colloid particles scatter light, solute Colloid particles scatter light, solute particles do notparticles do not

Factors affecting solubilityFactors affecting solubility

Difference in polarity between solute and solvent Difference in polarity between solute and solvent – like dissolves like– like dissolves like

TemperatureTemperature Solid solutes: depends on balance of several factors – Solid solutes: depends on balance of several factors –

can increase, decrease or stay the samecan increase, decrease or stay the same Gases: solubility always Gases: solubility always decreasesdecreases with temperature with temperature

Pressure Pressure Solids: little influenceSolids: little influence Gases: solubility always Gases: solubility always increasesincreases with pressure with pressure

(Henry’s law)(Henry’s law)

SaturationSaturation

A saturated solution is one which is in A saturated solution is one which is in equilibrium with undissolved solute – it has equilibrium with undissolved solute – it has reached limit of solubilityreached limit of solubility

Supersaturation arises when amount of Supersaturation arises when amount of substance in solution is greater than that substance in solution is greater than that predicted on basis of saturation. An predicted on basis of saturation. An essential condition for the growth of essential condition for the growth of crystalscrystals

Henry’s LawHenry’s Law

The number of moles of gas dissolved in a The number of moles of gas dissolved in a liquid is proportional to the partial pressure liquid is proportional to the partial pressure of the gasof the gas Exchange of COExchange of CO22 and O and O22 in respiration in respiration

depends on Henry’s Law.depends on Henry’s Law. In the lungs, the OIn the lungs, the O2 2 partial pressure is higher partial pressure is higher

than that of COthan that of CO22

In the blood, the COIn the blood, the CO2 2 pressure is higher after pressure is higher after

respirationrespiration

Real world applications 1:Real world applications 1:Henry’s Law and sodie popHenry’s Law and sodie pop

The quantity of gas dissolved in a liquid The quantity of gas dissolved in a liquid depends directly on the pressure of that depends directly on the pressure of that gas above the liquidgas above the liquid

Under pressure the COUnder pressure the CO22 in the liquid is in the liquid is

kept in solutionkept in solution Open the cap and the COOpen the cap and the CO22 rapidly escapes rapidly escapes

Real world applications 2:Real world applications 2:The science of breathingThe science of breathing

The gas laws explain the mechanics of The gas laws explain the mechanics of breathing: the transport of oxygen from the breathing: the transport of oxygen from the lungs and exchange with carbon dioxide lungs and exchange with carbon dioxide produced in the body.produced in the body.

Measuring concentration Measuring concentration

Concentration = amount of solute/amount Concentration = amount of solute/amount of solutionof solution

Weight/volume percentWeight/volume percent Mass solute in g/volume of soln in mL x 100%Mass solute in g/volume of soln in mL x 100%

Weight/weight percentWeight/weight percent Mass solute in g/mass solution in g x 100%Mass solute in g/mass solution in g x 100%

MolarityMolarity

Concentration is usually expressed in Concentration is usually expressed in terms of molarity:terms of molarity:

Moles of solute/liters of Moles of solute/liters of solutionsolution (M) (M)

Moles of solute = molarity x volume of solutionMoles of solute = molarity x volume of solution

Moles = M x VMoles = M x V

Molarity and concentrationMolarity and concentration

Molarity:Molarity:

M = moles solute/liter of solutionM = moles solute/liter of solution DilutionDilution

MM11VV11 = M = M22VV22

Dilution factor = VDilution factor = V22/V/V11 (V (V22>V>V11))

MM22<M<M11

ExampleExample

What is molarity of 50 ml solution containing What is molarity of 50 ml solution containing 2.355 g H2.355 g H22SOSO44?? Molar mass HMolar mass H22SOSO44 = 98.1 g/mol = 98.1 g/mol

Moles HMoles H22SOSO44 = .0240 mol = .0240 mol (2.355 g/98.1 g/mol)(2.355 g/98.1 g/mol)

Volume of solution = 50 mL/1000 mL/L = .050 LVolume of solution = 50 mL/1000 mL/L = .050 L Concentration = moles/volumeConcentration = moles/volume

= .0240 mol/.050 L = 0.480 M= .0240 mol/.050 L = 0.480 M

Solution stoichiometrySolution stoichiometry How much volume of one solution to react with another How much volume of one solution to react with another

solutionsolution Given volume of A with molarity MGiven volume of A with molarity MAA

Determine moles ADetermine moles A Determine moles BDetermine moles B Find target volume of B with molarity MFind target volume of B with molarity MBB

Volume Bmol = MV Mole:mole ratio V = mol/MVolume A Moles A Moles B

TitrationTitration

Use a solution of known concentration to Use a solution of known concentration to determine concentration of an unknowndetermine concentration of an unknown

Must be able to identify endpoint of Must be able to identify endpoint of titration to know stoichiometrytitration to know stoichiometry

Most common applications with acids and Most common applications with acids and basesbases

Colligative propertiesColligative properties

Properties that depend upon the Properties that depend upon the concentration of solute concentration of solute particlesparticles but not but not their identitytheir identity Vapor pressure loweringVapor pressure lowering Freezing point depressionFreezing point depression Boiling point elevationBoiling point elevation Osmotic pressureOsmotic pressure

Raoult’s lawRaoult’s law

When nonvolatile solute is When nonvolatile solute is added to solvent, vapor added to solvent, vapor pressure of solvent pressure of solvent decreases in proportion to decreases in proportion to concentration of soluteconcentration of solute Freezing point goes Freezing point goes downdown Boiling point goes Boiling point goes upup

Freezing and melting are dynamic Freezing and melting are dynamic processesprocesses

At equilibrium, rate of freezing = rate of meltingAt equilibrium, rate of freezing = rate of melting

Adding salts upsets the equilibriumAdding salts upsets the equilibrium

Fewer water molecules at Fewer water molecules at surface: rate of freezing surface: rate of freezing dropsdrops

Ice turns into liquidIce turns into liquid Lower temperature to Lower temperature to

regain balanceregain balance Depression of freezing Depression of freezing

pointpoint

The same model explains elevated The same model explains elevated boiling pointboiling point

Condensation and Condensation and evaporation are evaporation are dynamic processesdynamic processes

Replacing some of Replacing some of the liquid water with the liquid water with salt reduces rate of salt reduces rate of evaporation – leads to evaporation – leads to condensationcondensation

Raise temperature to Raise temperature to recover balancerecover balance

Mathematical baseMathematical base

Freezing point depressionFreezing point depression ΔΔTTf f = k= kff x solute concentration x solute concentration

Boiling point elevationBoiling point elevation ΔΔTTb b = k= kbb x solute concentration x solute concentration

Units of concentrationUnits of concentration

Effect depends upon Effect depends upon numbernumber of particles of particles not mass of particles, so concentration not mass of particles, so concentration must be in moles.must be in moles.

MolaMolallity (m)ity (m) is used in these situationsis used in these situations Moles solute/Moles solute/kg solventkg solvent Temperature independent measure of Temperature independent measure of

concentrationconcentration

Type of solute importantType of solute important

Covalent solute produces one particle per Covalent solute produces one particle per molecule:molecule: CC66HH1212OO6 6 (s) (s) → → CC66HH1212OO6 6 (aq)(aq)

Ionic solutes produce >1 particle per Ionic solutes produce >1 particle per formula unit:formula unit: NaCl (s) NaCl (s) → Na→ Na++(aq) + Cl(aq) + Cl--(aq) (2 particles)(aq) (2 particles) CaClCaCl22(s) → Ca(s) → Ca2+2+(aq) + 2Cl(aq) + 2Cl--(aq) (3 particles)(aq) (3 particles)

Osmotic pressureOsmotic pressure

Transport across Transport across semipermeablesemipermeable membranes:membranes: Solvent particles admitted but solute particles Solvent particles admitted but solute particles

rejectedrejected OsmosisOsmosis involves passage of water involves passage of water

molecules across a membranemolecules across a membrane

OsmosisOsmosis

Transport of water Transport of water molecules from dilute molecules from dilute solution to more solution to more concentrated oneconcentrated one

Imbalance of Imbalance of concentration provides concentration provides driving forcedriving force

Osmotic pressure is the Osmotic pressure is the pressure required to pressure required to oppose this flowoppose this flow

Osmotic pressureOsmotic pressure

Osmotic pressure is written as:Osmotic pressure is written as:

ππV = nRTV = nRT

Osmotic pressure

Volume

No moles

Gas constant

Temperature

Calculating osmotic pressureCalculating osmotic pressure

But n/V = concentration in moles per liter =MBut n/V = concentration in moles per liter =M

ππ = MRT (T in Kelvin) = MRT (T in Kelvin) But what molarity? Need to know moles of But what molarity? Need to know moles of

particlesparticles CC66HH1212OO66 = 1 mole particles = 1 mole particles NaCl = 2 moles of particlesNaCl = 2 moles of particles CaClCaCl22 = 3 moles of particles = 3 moles of particles

OsmolarityOsmolarity refers to concentration of particles for refers to concentration of particles for osmotic pressure determinationosmotic pressure determination

Osmotic pressure and cellsOsmotic pressure and cells Concentration in cells depends on osmosisConcentration in cells depends on osmosis

Concentration outside cell > inside (hypertonic) – Concentration outside cell > inside (hypertonic) – crenationcrenation

Concentration outside cell < inside (hypotonic) - Concentration outside cell < inside (hypotonic) - hemolysishemolysis

Crenation Hemolysis