SolutionsSolutions

Chapter 15Chapter 15

What Are Solutions?What Are Solutions?

Section 15.1Section 15.1

What Are Solutions?What Are Solutions?

• Solution: homogeneous mixture of 2 Solution: homogeneous mixture of 2 or more substancesor more substances– Solid, liquid, or gasSolid, liquid, or gas– Solvent: dissolving mediumSolvent: dissolving medium– Solute: substance that dissolvesSolute: substance that dissolves– When in solution, you cannot distinguish When in solution, you cannot distinguish

solvent and solutesolvent and solute

What is a Solution?What is a Solution?

• Soluble – a substance that can Soluble – a substance that can dissolve in a given solventdissolve in a given solvent– Miscible: two liquids that can dissolve in Miscible: two liquids that can dissolve in

each othereach other•Example: water and antifreezeExample: water and antifreeze

• Insoluble – substance cannot dissolveInsoluble – substance cannot dissolve– Immiscible: two liquids that cannot Immiscible: two liquids that cannot

dissolve in each otherdissolve in each other•Example: oil & waterExample: oil & water

Why Do Some Substances Why Do Some Substances Dissolve and not Others?Dissolve and not Others?• To dissolve, solute particles must To dissolve, solute particles must

dissociate from each other and mix dissociate from each other and mix with solvent particleswith solvent particles– Attractive forces between solute and Attractive forces between solute and

solvent must be greater than attractive solvent must be greater than attractive forces within the soluteforces within the solute

• Process of surrounding solute Process of surrounding solute particles with solvent particles is particles with solvent particles is called SOLVATIONcalled SOLVATION– In water, it is also called HYDRATIONIn water, it is also called HYDRATION

Aqueous Solutions of Ionic Aqueous Solutions of Ionic CompoundsCompounds• Remember:Remember:

– Water molecules are polar (+ and – ends)Water molecules are polar (+ and – ends)– Water molecules are in constant motionWater molecules are in constant motion

• When you put salt in water, water When you put salt in water, water molecules collide with surface of crystalmolecules collide with surface of crystal– Charged ends of water attract ions of saltCharged ends of water attract ions of salt– Dipole interaction (water/salt) is stronger Dipole interaction (water/salt) is stronger

than ions in crystal, so it pulls them awaythan ions in crystal, so it pulls them away

SolvationSolvation

Aqueous Solutions of Molecular Aqueous Solutions of Molecular CompoundsCompounds• Water is also a good solvent for many Water is also a good solvent for many

molecular compounds (Example: molecular compounds (Example: sugar)sugar)– Sugar has many O-H bonds (polar)Sugar has many O-H bonds (polar)– When water is added, the O-H bond When water is added, the O-H bond

becomes a site for hydrogen bonding with becomes a site for hydrogen bonding with waterwater

– Water’s hydrogen bonds pulls the sugar Water’s hydrogen bonds pulls the sugar molecules apartmolecules apart

– Oil is not a good solute because it has Oil is not a good solute because it has many C-H bonds (not polar) and few or no many C-H bonds (not polar) and few or no O-H (polar) bondsO-H (polar) bonds

Factors that Affect Solvation Factors that Affect Solvation RateRate• Increase Solvation Rate (Dissolve Increase Solvation Rate (Dissolve

Faster) by:Faster) by:– Agitation (stirring)Agitation (stirring)– Increase surface area (make particles Increase surface area (make particles

smaller)smaller)– Temperature (make it hotter)Temperature (make it hotter)

• All these increase the number of All these increase the number of collision between water and the collision between water and the solute solute

Heat of SolutionHeat of Solution

• During Solvation it takes energy to During Solvation it takes energy to make the solute particles come make the solute particles come apart.apart.

• Solvent particles must also move Solvent particles must also move apartapart

• This energy requirements is called This energy requirements is called “Heat of Solution”“Heat of Solution”

SolubilitySolubility• Has Anyone ever made rock candy?Has Anyone ever made rock candy?

– How much water does it take to dissolve the How much water does it take to dissolve the sugar at room temperature?sugar at room temperature?

– What happens when we raised the What happens when we raised the temperature?temperature?

• Only a limited amount of solute can Only a limited amount of solute can dissolve in a given amount of solventdissolve in a given amount of solvent

• Every solute is unique for the solventEvery solute is unique for the solvent

• This is ‘Solubility’ – the amount of solute This is ‘Solubility’ – the amount of solute that can dissolve in a given amount of that can dissolve in a given amount of solvent at a specified temperature and solvent at a specified temperature and pressurepressure

Solubility ContinuedSolubility Continued

• Solubility can also be understood at the Solubility can also be understood at the particle level:particle level:– As particles collide, some particles are As particles collide, some particles are

deposited back to the solutedeposited back to the solute– Some particles are removed from the solute.Some particles are removed from the solute.– When the rate of deposit equals the rate of When the rate of deposit equals the rate of

solvation, then the solution is SATURATEDsolvation, then the solution is SATURATED

• Saturated Solution – no more solute can Saturated Solution – no more solute can be dissolved in the solvent at this be dissolved in the solvent at this temperature and pressuretemperature and pressure

• Unsaturated Solution – there is still room Unsaturated Solution – there is still room for more solute to be dissovedfor more solute to be dissoved

Factors that Affect SolubilityFactors that Affect Solubility

• Most substances are MORE soluble at Most substances are MORE soluble at high temperature than at lowhigh temperature than at low– If you dissolve a substance until If you dissolve a substance until

saturated at high temperature and then saturated at high temperature and then reduce the temperature, the solution reduce the temperature, the solution becomes “supersaturated”becomes “supersaturated”

– Supersaturated solutions are unstableSupersaturated solutions are unstable•A small change makes the solute reappearA small change makes the solute reappear

•Rock candy worked that way. How?Rock candy worked that way. How?

Factors that Affect SolubilityFactors that Affect Solubility

• Pressure affects solubility of gaseous Pressure affects solubility of gaseous solutessolutes– Carbonated beveragesCarbonated beverages

• Henry’s LawHenry’s Law– At a given temperature solubility (S) of a At a given temperature solubility (S) of a

gas in a liquid is directly proportional to gas in a liquid is directly proportional to pressure (P)pressure (P)

S2 = S1P1

P2

ORS1

P1

= S2

P2

Solution ConcentrationSolution Concentration

Section 15.2Section 15.2

Expressing ConcentrationExpressing Concentration

• Concentration is a measure of how Concentration is a measure of how much solute is dissolved in a specific much solute is dissolved in a specific amount of solvent.amount of solvent.

• Concentration can be qualitative or Concentration can be qualitative or quantitativequantitative– Qualitative: strong, weak, etc.Qualitative: strong, weak, etc.– Quantitative: percent by mass, percent Quantitative: percent by mass, percent

by volume, molarity, molalityby volume, molarity, molality

Using Percent to Express Using Percent to Express ConcentrationConcentration

Percent by mass = Mass of soluteMass of solution

X 100

Percent by volume = Volume of soluteVolume of solution

X 100

MolarityMolarity

• Molarity is the most common method of Molarity is the most common method of expressing concentration in Chemistryexpressing concentration in Chemistry

• Molarity is moles of solute in 1 liter of Molarity is moles of solute in 1 liter of solution.solution.– You make it by taking 1 mole of a solute and You make it by taking 1 mole of a solute and

filling up with solvent to the 1 liter level.filling up with solvent to the 1 liter level.

Molarity (M) = Moles of soluteLiters of solution

Molarity - ExampleMolarity - Example An IV solution contains 5.10 g of glucose (C6H12O6) in 100.5ml of water. What is the molarity of this solution?

Known:Mass of solute = 5.10 g glucoseMolar mass of glucose = 180.0 g/molVolume of solvent = 100.5 ml

SOLVE for Mole/Liter:

5.10g glucose X 1 mol glucose180 g/mol glucose

= 0.028 mol glucose

Convert ml to liters:

100.5 ml X1 L1000 ml

= 0.1005 L

Molarity = MolesLiter

=0.028 mol0.1005 L

= 0.28 M

Preparing Molar SolutionsPreparing Molar Solutions

• How do you prepare a 1.5How do you prepare a 1.5M solution of sucrose (C12H22O11) ? ?

• 1.5 moles sucrose x 342g/mol = 513 g 1.5 moles sucrose x 342g/mol = 513 g sucrosesucrose

• 1.5 Molar would be 513g in 1 L of water1.5 Molar would be 513g in 1 L of water– Measure out 513 g sucroseMeasure out 513 g sucrose– Put it in a 1L graduated cylinderPut it in a 1L graduated cylinder– Add distilled water to make 1L total Add distilled water to make 1L total

solutionsolution

• To make 100ml, use 1/10To make 100ml, use 1/10thth of each of each– 51.3g sucrose in 100ml of water51.3g sucrose in 100ml of water

Making Dilute SolutionsMaking Dilute Solutions

• Concentrated HydroChloric Acid is Concentrated HydroChloric Acid is 1212MM..

• How would I make ½ the How would I make ½ the concentration, or 6 concentration, or 6 MM ? ?– Use MUse M11VV11 = M = M22VV22

– 12moles x 1L = 6moles x ?L12moles x 1L = 6moles x ?L

= 12moles x 1L/6 moles = 2 L= 12moles x 1L/6 moles = 2 L– So put in twice the solvent and you have So put in twice the solvent and you have

½ the concentration.½ the concentration.

Molality and Mole FractionMolality and Mole Fraction

• Molality is Moles of Solute per 1 kg of Molality is Moles of Solute per 1 kg of SolventSolvent– Abbreviated Abbreviated mm and is read as molal. and is read as molal.– This is because volume increases with This is because volume increases with

temperature and this changes the temperature and this changes the molarity.molarity.

Calculating MolalityCalculating Molality

• If a student adds 4.5 g of sodium chloride If a student adds 4.5 g of sodium chloride to 100.0g of water, what is the molality?to 100.0g of water, what is the molality?

Known:Mass of water is 100.0 gMass of sodium Chloride is 4.5g

Unknown: m or mol/kg

4.5g NaCl X 1 mol NaCl58.5 g NaCl

= 0.077 mol NaCl

100.0 g water X1 kg H2O1000 g H20

= 0.1000 kg H2O

m = Moles of soluteKg solvent

= 0.077 mol NaCl0.1000 kg H2O

= 0.77 mol/kg

Mole FractionMole Fraction

• Mole fraction = moles solute divided Mole fraction = moles solute divided by total moles of solute + solventby total moles of solute + solvent

Mole Fraction (X) = ___nA__nA + nB

Example: What is the mole fraction of hydrochloric acid if for every 100 g of solution, 37.5 g is HCl

37.5 g HCl x 1 Mol HCl36.5 g HCl

= 1.03 mol HCl

62.5 g H2O x 1 mole H2O18.0 g H2O

= 3.47 mol H2O

XHCl = ___nHCL___nHCl + nH2O

= _____1.03 mol HCl_______1.03 mol HCl + 3.47 mol H2O

= 0.229

Colligative Properties of Colligative Properties of SolutionsSolutions

Chapter 15.3Chapter 15.3

Electrolytes and Colligative Electrolytes and Colligative PropertiesProperties

• When solutions are made, the When solutions are made, the physical properties of the solutions physical properties of the solutions are affected by the number of are affected by the number of particle dissolvedparticle dissolved– Colligative: depending on the collectionColligative: depending on the collection

Colligative PropertiesColligative Properties

1.1. Electrolytes vs non-electrolytesElectrolytes vs non-electrolytes– Ionic compounds ARE electrolytes Ionic compounds ARE electrolytes

because they form ions in solution that because they form ions in solution that conduct electricityconduct electricity

– Molecular compounds ARE NOT Molecular compounds ARE NOT electrolytes because they do not electrolytes because they do not conduct electricityconduct electricity

2.2. Vapor Pressure LoweringVapor Pressure Lowering• Adding a non-volatile solute lowers the Adding a non-volatile solute lowers the

vapor pressure of the solution (vs. vapor pressure of the solution (vs. solvent)solvent)

• More solute More solute more vapor pressure more vapor pressure loweringlowering

Colligative PropertiesColligative Properties3.3. Boiling Point ElevationBoiling Point Elevation

• Because vapor pressure is lowered, it takes Because vapor pressure is lowered, it takes more energy to make it boilmore energy to make it boil• Boiling point temperature is raisedBoiling point temperature is raised• Boiling point elevation is directly proportional to Boiling point elevation is directly proportional to

solution molalitysolution molality• What is the benefit of adding salt to boiling water for What is the benefit of adding salt to boiling water for

pasta?pasta?

4.4. Freezing Point DepressionFreezing Point Depression• Freezing point temperature is loweredFreezing point temperature is lowered• Solute particles interfere with attractive forces Solute particles interfere with attractive forces

of solventof solvent• Freezing point of a solution is always lower Freezing point of a solution is always lower

than the freezing point of a pure solventthan the freezing point of a pure solvent• FP Depression is directly proportional to FP Depression is directly proportional to

molalitymolality

Colligative PropertiesColligative Properties

5.5. Osmosis and Osmotic PressureOsmosis and Osmotic Pressure• Diffusion: mixing of gasses or liquids Diffusion: mixing of gasses or liquids

through random motionsthrough random motions

• Osmosis is diffusion of solvent through a Osmosis is diffusion of solvent through a semi permeable membrane from high semi permeable membrane from high solvent concentration to lower solvent solvent concentration to lower solvent concentrationconcentration– Living cells use this to get materials in/out of Living cells use this to get materials in/out of

cellscells

Colligative PropertiesColligative Properties• Example: Salt/waterExample: Salt/water

– During Osmosis, Water molecules move During Osmosis, Water molecules move both directions through membraneboth directions through membrane•But only water can move through the But only water can move through the

membranemembrane•So pure water builds up on one side of the So pure water builds up on one side of the

membranemembrane•Water/salt builds up on the other.Water/salt builds up on the other.

– Higher concentration of water on one Higher concentration of water on one side creates:side creates:•Osmotic pressureOsmotic pressure•A pressure or push to equalize the water/salt A pressure or push to equalize the water/salt

concentrationsconcentrations•Pressure depends on concentration of solutePressure depends on concentration of solute

Colligative Properties - Colligative Properties - AntifreezeAntifreeze

Antifreeze Colligative Properties

-100

-50

0

50

100

150

200

250

0 10 20 30 40 50 60

% by Volume

Tem

per

atu

re (

F)

Series1

Series2

B. TypesB. Types

View Flash animation.

Freezing Point DepressionFreezing Point Depression

B. TypesB. Types

Solute particles reduce vapor pressure of solvent, requiring more energy for vapor pressure Solute particles reduce vapor pressure of solvent, requiring more energy for vapor pressure to reach atmospheric pressure (boiling), thus raising the boiling point temperature.to reach atmospheric pressure (boiling), thus raising the boiling point temperature.

Boiling Point ElevationBoiling Point Elevation

B. TypesB. Types

• ApplicationsApplications– salting icy roadssalting icy roads– making ice creammaking ice cream– antifreezeantifreeze

•cars (-64°C to 136°C)cars (-64°C to 136°C)

•fish & insectsfish & insects

C. CalculationsC. Calculations

tt:: change in temperaturechange in temperature ( (°°CC))

kk:: constant constant basedbased on the solvent on the solvent ((°°CC··kgkg//molmol))

mm:: molalitymolality ( (mm))

nn:: # of particles# of particles

t = k · m · n

C. CalculationsC. Calculations• # of Particles# of Particles

– Nonelectrolytes (covalent)Nonelectrolytes (covalent)• remain intact when dissolved remain intact when dissolved • 1 particle1 particle

– Electrolytes (ionic)Electrolytes (ionic)• dissociate into ions when dissolveddissociate into ions when dissolved• 2 or more particles2 or more particles

C. CalculationsC. Calculations

• At what temperature will a solution that is composed At what temperature will a solution that is composed of 0.73 moles of glucose in 225 g of phenol boil?of 0.73 moles of glucose in 225 g of phenol boil?

m = 3.2mn = 1tb = kb · m · n

WORK:

m = 0.73mol ÷ 0.225kg

GIVEN:b.p. = ?tb = ?

kb = 3.60°C·kg/moltb = (3.60°C·kg/mol)(3.2m)(1)

tb = 12°C

b.p. = 181.8°C + 12°C

b.p. = 194°C

C. CalculationsC. Calculations

• Find the freezing point of a saturated solution Find the freezing point of a saturated solution of NaCl containing 28 g NaCl in 100. mL water.of NaCl containing 28 g NaCl in 100. mL water.

m = 4.8m

n = 2

tf = kf · m · n

WORK:

m = 0.48mol ÷ 0.100kg

GIVEN:

f.p. = ?

tf = ?

kf = 1.86°C·kg/mol

tf = (1.86°C·kg/mol)(4.8m)(2)

tf = 18°C

f.p. = 0.00°C - 18°C

f.p. = -18°C

Heterogeneous MixturesHeterogeneous Mixtures

Chapter 15.4Chapter 15.4

Types of Heterogeneous Types of Heterogeneous MixturesMixtures• Heterogeneous MixturesHeterogeneous Mixtures

– Look like a solution, but are really Look like a solution, but are really mixturesmixtures

– Mixtures of substances that exist in 2 Mixtures of substances that exist in 2 different phasesdifferent phases

• 2 Types:2 Types:– SuspensionsSuspensions– ColloidsColloids

• Solutions:Solutions:– Particles of solute are atomic sized Particles of solute are atomic sized

compared to solventcompared to solvent

SuspensionsSuspensions

• Particle SizeParticle Size– Suspended particles are large compared Suspended particles are large compared

to solvent to solvent •Larger than 1000 nm for solvated particlesLarger than 1000 nm for solvated particles

– CAN be filteredCAN be filtered•When stirred, solid-like state begins to flow When stirred, solid-like state begins to flow

like a liquidlike a liquid– Called ThixotropicCalled Thixotropic

•ExamplesExamples– housepainthousepaint

ColloidsColloids

• Particle SizeParticle Size– Particles of solute are intermediate sized Particles of solute are intermediate sized

(between atomic and large suspension (between atomic and large suspension sized) compared to solventsized) compared to solvent

– Between 1 nm and 1000 nm diameterBetween 1 nm and 1000 nm diameter

• Cannot be Separated by filtration or Cannot be Separated by filtration or settlingsettling– Example: milk, butter, cheese, Example: milk, butter, cheese,

ColloidsColloids

• Types of ColloidsTypes of Colloids– Solid Sol: Solid in solid (gemstones)Solid Sol: Solid in solid (gemstones)– Sol: Solid in Liquid (Blood, gelatin)Sol: Solid in Liquid (Blood, gelatin)– Solid emulsion: Liquid in solid (butter, cheese)Solid emulsion: Liquid in solid (butter, cheese)– Emulsion: liquid/liquid (milk, mayonaise)Emulsion: liquid/liquid (milk, mayonaise)– Solid foam: gas/solid (marshmallows, soap that Solid foam: gas/solid (marshmallows, soap that

floats)floats)– Foam: gas/liquid (whipped cream, beaten egg Foam: gas/liquid (whipped cream, beaten egg

whites)whites)– Aerosol: solid/gas (smoke, dust in air)Aerosol: solid/gas (smoke, dust in air)– Aerosol: liquid/gas (clouds, spray deodorantAerosol: liquid/gas (clouds, spray deodorant

Brownian MotionBrownian Motion

• Liquid colloid under a microscope Liquid colloid under a microscope shows random, jerky motions of shows random, jerky motions of dispersed particlesdispersed particles– Brownian motionBrownian motion– From collisions of particles of dispersion From collisions of particles of dispersion

medium with dispersed particlesmedium with dispersed particles– Collisions prevent particles from settling Collisions prevent particles from settling

outout– Due to polar or charged atomic particlesDue to polar or charged atomic particles

• Link for displayLink for display– http://www.phy.ntnu.edu.tw/ntnujava/inhttp://www.phy.ntnu.edu.tw/ntnujava/in

dex.php?topic=24dex.php?topic=24

Tyndall EffectTyndall Effect

• Dilute Colloids sometimes appear as Dilute Colloids sometimes appear as clear solutions (concentrated colloids clear solutions (concentrated colloids do not)do not)– Because particles are too small to be Because particles are too small to be

seen with naked eyeseen with naked eye– But: dispersed colloid particles are large But: dispersed colloid particles are large

enough to scatter lightenough to scatter light•Tyndall effectTyndall effect

– Solutions do not scatter light (particles Solutions do not scatter light (particles are too small)are too small)

Tyndall EffectTyndall Effect

SolutionColloid

Chapter SummaryChapter Summary

• Chapter 15 Test on Friday (5/16)Chapter 15 Test on Friday (5/16)

• Chapter 15 Vocabulary Due Friday Chapter 15 Vocabulary Due Friday (5/16)(5/16)

• Chapter 15 HO’s (remaining) Due Chapter 15 HO’s (remaining) Due Friday (5/16)Friday (5/16)

Chapter Test Covers:Chapter Test Covers:

• Characteristics of SolutionsCharacteristics of Solutions– Solvation – ionic vs molecularSolvation – ionic vs molecular– Factors Affecting SolubilityFactors Affecting Solubility

• Solution Concentrations: CalculateSolution Concentrations: Calculate– Percent by massPercent by mass– Percent by volumePercent by volume– MolarityMolarity– MolalityMolality

• Colligative Properties of SolutionsColligative Properties of Solutions• Suspensions and ColloidsSuspensions and Colloids