What Are Solutions?What Are Solutions?

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?

SolubilitySolubility

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTIONmore solute dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

concentration

SolubilitySolubility• Solubility Solubility

CurveCurve– shows the shows the

dependence of dependence of solubility on solubility on temperaturetemperature

Solubility ChartSolubility Chart

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

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

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

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

The ammeter measures the flow of electrons (current) through the circuit.

If the ammeter measures a current, and the bulb glows, then the solution conducts.

If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting.

Electrolytes vs. Electrolytes vs. NonelectrolytesNonelectrolytes

An electrolyte is:

  A substance whose aqueous solution conducts an electric current.

A nonelectrolyte is:

  A substance whose aqueous solution does not conduct an electric current.

Try to classify the following substances as electrolytes or nonelectrolytes…

Definition of Electrolytes and Definition of Electrolytes and NonelectrolytesNonelectrolytes

1.Pure water 2.Tap water 3.Sugar solution 4.Sodium chloride solution 5.Hydrochloric acid solution 6.Lactic acid solution 7.Ethyl alcohol solution 8.Pure sodium chloride

Electrolytes?Electrolytes?

ELECTROLYTES: NONELECTROLYTES:

  Tap water (weak)

  NaCl solution

  HCl solution

  Lactate solution (weak)

 

 

  Pure water

  Sugar solution

  Ethanol solution

  Pure NaCl

  But why do some compounds conduct electricity in solution while others do not…?

Answers to ElectrolytesAnswers to Electrolytes