Chapter 15Chapter 15

SolutionsSolutions

15.1 What are solutions?15.1 What are solutions?A. Characteristics of SolutionsA. Characteristics of Solutions 1. Solutions are homogeneous mixtures 1. Solutions are homogeneous mixtures

containing two or more substances containing two or more substances called the solute and the solvent. called the solute and the solvent.

The The solutesolute is the is the

substance that dissolves.substance that dissolves. The The solventsolvent is the is the

dissolving mediumdissolving medium..

The The solutesolute is is the the

substance that substance that dissolves.dissolves.

The The solventsolvent is is the the

dissolving dissolving medium.medium.

Solutions may exist as Solutions may exist as solids, liquids, or gasessolids, liquids, or gases• Ex: air, brass, salt waterEx: air, brass, salt water

• But most solutions are liquidBut most solutions are liquid

SolutionsSolutions

Air:gas in gas

Seawater:solids in water

Soft drinks:gas in liquid

SolutionsSolutions

Brass:solid in solid

Fog:Liquid in gas

Solution TermsSolution Terms

Soluble-Soluble- dissolves in a solvent dissolves in a solvent

Insoluble-Insoluble- does not dissolve in a does not dissolve in a solvent solvent

Miscibility, the ability Miscibility, the ability of liquids to mix. Think of liquids to mix. Think of it as “mixibility”!of it as “mixibility”!

Oil and water are Oil and water are immiscibleimmiscible. They won’t . They won’t mix. mix. That’s why you That’s why you have to mix oil and have to mix oil and vinegar before you vinegar before you pour it in a salad.pour it in a salad.

Immiscible-Immiscible- one is one is insoluble in the other insoluble in the other and do not mix. and do not mix.

Miscible -Miscible - two liquids two liquids that are soluble in that are soluble in each other and will each other and will mixmix. .

Water and alcohol Water and alcohol are miscible.are miscible.

Likewise, chocolate Likewise, chocolate syrup and milk are syrup and milk are miscible.miscible.

Dissolution in Aqueous Dissolution in Aqueous SolutionsSolutions

Dissolution-Dissolution- process of process of surrounding solute particles with surrounding solute particles with solvent particles to form a solvent particles to form a solutionsolution..

Water has polarity:Water has polarity: a positive and a negative region. a positive and a negative region.

When a solute such as salt, is added When a solute such as salt, is added to a solvent such as water, the to a solvent such as water, the solvent particles surround it.solvent particles surround it.

The solvent particles pull the solute The solvent particles pull the solute particles apart .particles apart .

Dissolution - the solute particles are Dissolution - the solute particles are surrounded with solvent particles surrounded with solvent particles

forming a solution.forming a solution.The ions are completely The ions are completely

surrounded by the surrounded by the water molecules.water molecules.

Show phet videoShow phet video

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.html

““Like dissolves Like”Like dissolves Like”

Determines whether solvation will Determines whether solvation will occur in a specific solvent.occur in a specific solvent.

Determine the polarity of the Determine the polarity of the particles.particles.

Polar solutes dissolve in Polar Polar solutes dissolve in Polar solventssolvents

Nonpolar solutes dissolve in Nonpolar solutes dissolve in nonpolar solvents.nonpolar solvents.

A crystal of iodine (IA crystal of iodine (I22) is ) is in water on the left.in water on the left.

And in carbon And in carbon tetrachloride on the tetrachloride on the right.right.

The purple iodine The purple iodine crystal remains un-crystal remains un-dissolved in the water dissolved in the water but has dissolved in the but has dissolved in the carbon tetrachloride.carbon tetrachloride.

Water is polar, Iodine is Water is polar, Iodine is not.not.

So what is Carbon So what is Carbon tetrachloride, polar or tetrachloride, polar or non-polar?non-polar?

Aqueous solutions of ionic Aqueous solutions of ionic compoundscompounds

Water molecules are dipoles with Water molecules are dipoles with positive and negative ends and Ionic positive and negative ends and Ionic compounds have positive and compounds have positive and negative ions. negative ions. BOTH POLAR “like”BOTH POLAR “like”

So Ionic compounds dissolve easily So Ionic compounds dissolve easily in water.in water.

InsolubilityInsolubility Insolubility occurs because attractive Insolubility occurs because attractive

forces among the ions are so strong forces among the ions are so strong they can not be overcome by the they can not be overcome by the water molecules. water molecules.

Precipitates form.Precipitates form. If no dissolution, no solution is If no dissolution, no solution is

formedformed..

Aqueous solutions of molecular Aqueous solutions of molecular compoundscompounds

If a molecular compound is polar it If a molecular compound is polar it will dissolve in water. will dissolve in water.

Ex: sucrose Ex: sucrose Oil does not dissolve in water Oil does not dissolve in water

because it is nonpolar. “not like”because it is nonpolar. “not like”

Factors that affect rate of SolvationFactors that affect rate of Solvation

How can we dissolve sugar faster in our iced tea?

1. Agitating the mixture.

Stir the sugar. This increases the contact with unsaturated tea.

Increasing Rate of Increasing Rate of DissolvingDissolving

How can we dissolve sugar faster in our iced tea?

2. Increase the surface area. Use smaller crystals like powdered sugar instead of lumps. This increases the surface area of the sugar in the tea.

Powdered sugar

Increasing Rate of Increasing Rate of DissolvingDissolving

How can we dissolve sugar faster in our iced tea?

3. Temperature. Add the sugar to the hot tea before you add the ice.

SolubilitySolubility

Solubility Solubility – the maximum amount of – the maximum amount of solute that will dissolve in a given solute that will dissolve in a given amount of amount of solvent at a specified solvent at a specified temperature and pressure.temperature and pressure.

Crystallize – as the Crystallize – as the number of solvated number of solvated particles increases, particles increases, colliding solute colliding solute particles rejoin the particles rejoin the crystal.crystal.

Types of SolubilityTypes of SolubilitySaturated Solution-Saturated Solution- contains the contains the

maximum amount of dissolved solute maximum amount of dissolved solute for a given amount of solvent at a for a given amount of solvent at a specific temperature and pressure.specific temperature and pressure.

over all amount of dissolved solute over all amount of dissolved solute remains constant.remains constant.

Unsaturated Solution- Unsaturated Solution- contains contains less dissolved solute for a given less dissolved solute for a given temperature and pressure than a temperature and pressure than a saturated solution.saturated solution.

more solute can be dissolvedmore solute can be dissolved

• Supersaturated solutionSupersaturated solution – contains – contains more dissolved solute than a more dissolved solute than a saturated solution at the same saturated solution at the same temperature.temperature.

• Formed from a saturated solution at Formed from a saturated solution at a high temperature and then cool a high temperature and then cool slowly.slowly.

• Unstable – crystallize quicklyUnstable – crystallize quickly

Factors that Affect SolubilityFactors that Affect SolubilityTemperature and PressureTemperature and PressureTemperature Temperature - many substances are more - many substances are more

soluble at higher temperatures than at lower soluble at higher temperatures than at lower temperaturestemperatures

Solids generally dissolve faster in hot solutions than in cold solutions.

Gases dissolve faster in cold solutions than in warm solutions.

Temperature & SolubilityTemperature & Solubility

If we raise the temperature from 0C to 80C the solubility of NaCl (table salt) increases by only 2g/100 ml of H20. However, KNO3 (potassium nitrate) increases by 150g.

Temperature and SolubilityTemperature and Solubilityin Gasesin Gases

The trend for solubility in gases is different. As the temperature increases the solubility decreases.

Open a cold can of soda and a warm can of soda. Which will have the greatest rush of gas?

Will more oxygen be dissolved in a cold stream or a warm stream?

Solubility RulesSolubility Rules

All common compounds of Group I and ammonium ions are soluble. All common compounds of Group I and ammonium ions are soluble. All nitrates, acetates, and chlorates are soluble. All nitrates, acetates, and chlorates are soluble. All binary compounds of the halogens (other than F) with metals are All binary compounds of the halogens (other than F) with metals are

soluble, except those of Ag, Hg(I), and Pb. Pb halides are soluble in soluble, except those of Ag, Hg(I), and Pb. Pb halides are soluble in hot water.) hot water.)

All sulfates are soluble, except those of barium, strontium, calcium, All sulfates are soluble, except those of barium, strontium, calcium, lead, silver, and mercury (I). The latter three are slightly soluble. lead, silver, and mercury (I). The latter three are slightly soluble.

Except for rule 1, carbonates, hydroxides, oxides, silicates, and Except for rule 1, carbonates, hydroxides, oxides, silicates, and phosphates are insoluble. phosphates are insoluble.

Sulfides are insoluble except for calcium, barium, strontium, Sulfides are insoluble except for calcium, barium, strontium, magnesium, sodium, potassium, and ammonium. magnesium, sodium, potassium, and ammonium.

Salt (NaCl) is very soluble in water. 350 g/liter. However, if water evaporates, there will be too much salt for the water to hold in solution. The salt begins to form crystals.

A lake near Death Valley is supersaturated with salt causing the salt to crystallize out.A lake near Death Valley is supersaturated with salt causing the salt to crystallize out.

Pressure and SolubilityPressure and Solubility

SolubilitySolubility

increases asincreases as

ExternalExternal

PressurePressure

increasesincreases

Pressure and SolubilityPressure and Solubility

Ex: soda; as can is Ex: soda; as can is opened, pressure opened, pressure decreases, causing COdecreases, causing CO22

to come out of the to come out of the solutionsolution

Solids are not generally affected by pressure.

Gases dissolve faster under pressure.

Pressure and SolubilityPressure and Solubility

Scuba divers have a threat with dissolved nitrogen in the blood. During a deep descent there is increased pressure and more nitrogen can be dissolved in the blood. As the diver surfaces the nitrogen can form bubbles just like your can of soda. This is called “bends” and can be very painful and cause paralysis or death. Divers must be put into pressure chambers and slowly decrease pressure.

Electrolytes and Colligative Electrolytes and Colligative PropertiesProperties

Electrolytes form a solution that conducts Electrolytes form a solution that conducts electric current.electric current.

Strong – produce many ions in solution Strong – produce many ions in solution Ex: Sodium chlorideEx: Sodium chloride

Weak – produce only a few ions in Weak – produce only a few ions in solution solution

Ex: Ex: NaCl – 2 ionsNaCl – 2 ions

MgClMgCl22 – 3 ions – 3 ions

Conductivity TestingConductivity Testing

Relative amounts of salts can be detected in water using a “conductivity meter”. The meter sends an electric current through the solution. The strength of the current is proportional to the concentration of dissolved electrolytes

Nonelectrolytes in Aqueous Nonelectrolytes in Aqueous SolutionSolution

Nonelectrolyte- molecular Nonelectrolyte- molecular compound that dissolve in compound that dissolve in solvents but do not ionize, and solvents but do not ionize, and so do not conduct an electrical so do not conduct an electrical currentcurrentEx: sucroseEx: sucrose

15.2 Solution Concentration15.2 Solution Concentration

Concentration-Concentration- a measure of how a measure of how much solute is dissolved in a specific much solute is dissolved in a specific amount of solvent or solutionamount of solvent or solution

Expressing ConcentrationExpressing Concentration

Commonly used quantitative Commonly used quantitative expressions for concentration are:expressions for concentration are: Percent by MassPercent by Mass Percent by VolumePercent by Volume MolarityMolarity MolalityMolality

MolarityMolarity

Molarity-Molarity- number of moles of solute number of moles of solute dissolved per liter of solutiondissolved per liter of solution

Unit is Unit is MM, which stands for molar, which stands for molar

Molarity EquationMolarity Equation

Molarity (Molarity (MM) = ) = Moles of SoluteMoles of Solute

Liters of SolutionLiters of Solution

Diluting SolutionsDiluting Solutions

Increasing solvent decreases Increasing solvent decreases concentration, so:concentration, so:

VV11 M M1 1 = V = V22 M M22

ExamplesExamples

A 100.5 ml intravenous (IV) solution A 100.5 ml intravenous (IV) solution contains 5.10 grams of glucose (Ccontains 5.10 grams of glucose (C66HH1212OO66). ).

What is the What is the molaritymolarity of this solution? of this solution?

Steps for SolvingSteps for Solving1.1. Change all grams to molesChange all grams to moles

2.2. Change all liquid units to litersChange all liquid units to liters

3.3. Molarity = Molarity = Moles of soluteMoles of solute Liters of solutionLiters of solution

Grams to molesGrams to moles5.10 grams glucose 5.10 grams glucose (given)(given)

180.16 g glucose (molar mass of glucose)180.16 g glucose (molar mass of glucose)

= = 0.0283 mols glucose0.0283 mols glucose

Change all liquid units to litersChange all liquid units to liters100.5 ml 100.5 ml

1000 ml = 0.1005 Liters1000 ml = 0.1005 Liters

Calculate molarityCalculate molarity0.0283 (mols)0.0283 (mols)

0.1005 (Liters) = 0.1005 (Liters) = 0.282M0.282M

Dilution ExamplesDilution Examples

StepsSteps

1.1.Write formula : VWrite formula : V11MM11= V= V22MM22

2.2.List all the information you haveList all the information you have

3.3.Solve for unknownSolve for unknown

4.4.Check your units!Check your units!

Helpful hintsHelpful hints

M1V1M1V1 Starts with the words” Starts with the words”

stock solution”stock solution” Beginning solutionBeginning solution Original solutionOriginal solution Starting solutionStarting solution

M2V2M2V2 New solutionNew solution DilutionDilution Ending solutionEnding solution

ProblemProblem What volume in milliliters of 2.00M calcium What volume in milliliters of 2.00M calcium

chloride (CaClchloride (CaCl22) stock solution would you ) stock solution would you

use to make 0.50L of 0.300M calcium use to make 0.50L of 0.300M calcium chloride?chloride?

StepsSteps

MM11VV11= M= M22VV22

MM11 = 2.00 M = 2.00 M

MM22 = 0.300 M = 0.300 M

VV22 = 0.50 L = 0.50 L

VV11= ?= ?

MM11VV11= M= M22VV22

2.00 M (V2.00 M (V11) = 0.300M X0.5L) = 0.300M X0.5L

= 0.075 L= 0.075 L

Change to correct unitsChange to correct units 0.075 L X 1000 = 75 ml 0.075 L X 1000 = 75 ml

Practice ProblemsPractice Problems

Page 465 # Page 465 # 1414 and 16, 18,20 and 16, 18,20 2121 and 23. and 23.

http://conmedisys.com/play/VTmfQUNLlMY/Chemistry_Music_Video_24%253A_For_Those_About_To_Dissolve_We_Solute_You.html

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15.3 Colligative Properties 15.3 Colligative Properties of Solutionsof Solutions

Solutes affect some of the physical Solutes affect some of the physical properties of their solvents.properties of their solvents.

Colligative propertiesColligative properties – physical – physical properties of solutions that are properties of solutions that are affected by the number of particles affected by the number of particles but not by the type of dissolved but not by the type of dissolved solute particles.solute particles.

44 Colligative Properties Colligative Properties

Vapor Pressure Lowering-Vapor Pressure Lowering-Boiling Point Elevation-Boiling Point Elevation-Freezing Point Depression-Freezing Point Depression-Osmotic Pressure-Osmotic Pressure-

Vapor Pressure LoweringVapor Pressure Lowering

vapor pressure – the pressure vapor pressure – the pressure exerted in a closed container by liquid exerted in a closed container by liquid particles that have escaped the particles that have escaped the liquid’s surface and entered the liquid’s surface and entered the gaseous state.gaseous state.

vapor pressure loweringvapor pressure lowering - lowers - lowers the solvent’s vapor pressure by the solvent’s vapor pressure by adding a nonvolatile solute.adding a nonvolatile solute.

vapor pressure loweringvapor pressure lowering - lowers the - lowers the solvent’s vapor pressure by adding a solvent’s vapor pressure by adding a nonvolatile solute.nonvolatile solute.

fewer solvent particles enter the fewer solvent particles enter the gaseous state.gaseous state.

electrolytes – greater number of electrolytes – greater number of ions produced, the greater the ions produced, the greater the effect on vapor pressure.effect on vapor pressure.

Boiling Point ElevationBoiling Point Elevation

Since adding a solute lowers vapor Since adding a solute lowers vapor pressure, and boiling occurs when vapor pressure, and boiling occurs when vapor pressure equals atmospheric pressure. pressure equals atmospheric pressure.

The solution must be heated to a higher The solution must be heated to a higher temperature to raise the vapor pressure temperature to raise the vapor pressure to atmospheric pressure.to atmospheric pressure.

boiling point elevationboiling point elevation – temperature – temperature difference between a solution’s boiling difference between a solution’s boiling point and a pure solvent’s boiling point.point and a pure solvent’s boiling point.

The greater the number of solute The greater the number of solute particles in the solution, the greater the particles in the solution, the greater the boiling point elevation.boiling point elevation.

Example: adding salt to water to boil Example: adding salt to water to boil spaghetti. Water boils at 100spaghetti. Water boils at 10000C but when C but when salt is dissolved in it, it boils at 101.7salt is dissolved in it, it boils at 101.700C.C.

Freezing Point DepressionFreezing Point Depression

In a solution, the solute particles In a solution, the solute particles interfere with the attractive forces interfere with the attractive forces among the solvent particles. among the solvent particles.

Prevents it from becoming a solid at Prevents it from becoming a solid at

its normal freezing point.its normal freezing point.

The freezing point of a solution is always lower The freezing point of a solution is always lower than that of a pure solvent.than that of a pure solvent.

Freezing point depressionFreezing point depression – is the difference – is the difference in temperature between the solution’s freezing in temperature between the solution’s freezing point and the freezing point of its pure solvent.point and the freezing point of its pure solvent.

Example: Adding salt to the roads in cold Example: Adding salt to the roads in cold climates to prevent ice from forming. The salt climates to prevent ice from forming. The salt lowers the freezing point of water, so the ice lowers the freezing point of water, so the ice freezes at -5.9freezes at -5.900C instead of 0 C instead of 0 00C. C.

Ice-cream labIce-cream lab

Osmosis and Osmotic PressureOsmosis and Osmotic Pressure

DiffusionDiffusion is the mixing of gases or liquids is the mixing of gases or liquids resulting from their random motions.resulting from their random motions.

Osmosis Osmosis is the diffusion of solvent is the diffusion of solvent particles across a semi-permeable particles across a semi-permeable membrane from an area of higher solvent membrane from an area of higher solvent concentration to an area of lower solvent concentration to an area of lower solvent concentration.concentration.

Osmotic pressureOsmotic pressure – amount of – amount of additional pressure caused by the additional pressure caused by the water molecules that moved into the water molecules that moved into the solution.solution.

depends on the number of solute depends on the number of solute particles in a given volume of particles in a given volume of solution.solution.

Example of uses of Osmotic Example of uses of Osmotic PressurePressure

Salting to protect meat from bacterial spoilage Bacteria on meat die because the water gets sucked out of the cells by osmosis Concentrates the flavor of the meat 1lb of aged rib eye id $190.00!

15.4 Heterogeneous 15.4 Heterogeneous MixturesMixtures

contain substances that exist contain substances that exist in distinct phases.in distinct phases.Suspensions (largest particles)Suspensions (largest particles)Colloids (medium size particles)Colloids (medium size particles)

Relative Sizes of ParticlesRelative Sizes of Particles

Type of MixtureType of Mixture Size of ParticleSize of Particle

SolutionSolution Less than 1 nmLess than 1 nm

ColloidColloid Between 1 nm Between 1 nm and 1000 nmand 1000 nm

SuspensionSuspension Greater than Greater than

1000 nm1000 nm

SuspensionsSuspensions

SuspensionsSuspensions – a mixture – a mixture containing particles that settle out containing particles that settle out if left undisturbed.if left undisturbed.

Ex: cornstarch and water, fine Ex: cornstarch and water, fine sand and water, muddy watersand and water, muddy water

Separate by settling or by filtrationSeparate by settling or by filtration Suspended particles are large Suspended particles are large

1000 nm, compared to solvated 1000 nm, compared to solvated particles 1nm particles 1nm

thixotropic – solid state flows like a thixotropic – solid state flows like a liquid. Ex: house paintliquid. Ex: house paint

ColloidsColloids

ColloidsColloids - - heterogeneous mixture heterogeneous mixture of intermediate size particles of intermediate size particles

1nm to 1000 nm1nm to 1000 nmThe dispersion medium is the The dispersion medium is the

most abundant substance in the most abundant substance in the mixture.mixture.

ColloidsColloids Categorized according to the phases of Categorized according to the phases of

their dispersed particles and dispersing their dispersed particles and dispersing mediums.mediums. solssols - fine solid particles in a liquid - fine solid particles in a liquid

medium. Ex: paintmedium. Ex: paint emulsionemulsion - liquid particles in a liquid - liquid particles in a liquid

medium Ex: milkmedium Ex: milk aerosolaerosol – small liquid particles are – small liquid particles are

dispersed in a gas. Ex: fogdispersed in a gas. Ex: fog

Fog, whipped cream, mayonnaise, Fog, whipped cream, mayonnaise, and smoke are Colloidsand smoke are Colloids

Types of ColloidsTypes of Colloids

SolSol Blood, Jell-oBlood, Jell-o Solid in a LiquidSolid in a Liquid

Solid emulsionSolid emulsion Butter, CheeseButter, Cheese Liquid in a SolidLiquid in a Solid

EmulsionEmulsion Milk, MayonnaiseMilk, Mayonnaise Liquid in a LiquidLiquid in a Liquid

Solid foamSolid foam MarshmallowMarshmallow Gas in a SolidGas in a Solid

FoamFoam Whipped CreamWhipped Cream Gas in a LiquidGas in a Liquid

AerosolAerosol SmokeSmoke Solid in a GasSolid in a Gas

AerosolAerosol Hairspray, FogHairspray, Fog Liquid in a GasLiquid in a Gas

Brownian MotionBrownian Motion

Brownian Motion-Brownian Motion- erratic movement of erratic movement of colloid particlescolloid particles Results from Results from

collisions of particles collisions of particles of dispersing of dispersing medium with the medium with the dispersed particlesdispersed particles

The dispersed particles have polar The dispersed particles have polar atomic groups on their surface that atomic groups on their surface that attract the dispersing medium attract the dispersing medium particles. This prevents the colloid particles. This prevents the colloid particles from settling out of the particles from settling out of the mixture.mixture.

Stir in an electrolyte or add heat Stir in an electrolyte or add heat and the colloid is destroyed.and the colloid is destroyed.

Tyndall EffectTyndall Effect

Tyndall EffectTyndall Effect

Dilute colloids appear Dilute colloids appear to be homogeneous to be homogeneous because their because their dispersed particles are dispersed particles are so small.so small.

Tyndall effectTyndall effect – – dispersed colloid dispersed colloid particles are large particles are large enough to scatter light.enough to scatter light.

Ex: light rays through fog, sunlight Ex: light rays through fog, sunlight through smoke-filled airthrough smoke-filled air

Allows us to distinguish between Allows us to distinguish between colloid and solutionscolloid and solutions

Solutions never exhibit the Tyndall Solutions never exhibit the Tyndall effect.effect.

Colloids and suspensions exhibit the Colloids and suspensions exhibit the Tyndall effectTyndall effect..