Back Bires, 2010 Slide 1 Chapter 13, (14): Mixtures and Aqueous Solutions What are they? Where do we find them? How do we describe them? We use solutions

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Bires, 2010 Slide 1

Chapter 13, (14):Chapter 13, (14):MixturesMixtures and and Aqueous Aqueous

SolutionsSolutions

What are they?What are they?

Where do we find them?Where do we find them?

How do we describe them?How do we describe them?

We use solutions all the time

2211 VMVM

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Bires, 2010 Slide 2

Soluble and Soluble and InsolubleInsoluble• Soluble Soluble means: means: able to be dissolvedable to be dissolved..

• Ionic solidsIonic solids (made of cation and anion) (made of cation and anion) dissociate into their ionsdissociate into their ions in water. in water.

• Covalent solidsCovalent solids (like sugar) dissolve when (like sugar) dissolve when they are they are relatively polarrelatively polar..

• The dissolved particles cannot be easily The dissolved particles cannot be easily seen or separated from the solution.seen or separated from the solution.

• ““Like dissolves like”Like dissolves like”

• Alloys are solutions of metals!Alloys are solutions of metals!

• Solubility depends upon temperature…Solubility depends upon temperature…

Dissolution of NaCl.mov

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Bires, 2010 Slide 3

Increasing temperature Increasing temperature increasesincreases the the solubility of solubility of solidssolids in liquids in liquids

Increasing temperature Increasing temperature decreasesdecreases the the solubility of solubility of gassesgasses in liquids! … in liquids! …

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Bires, 2010 Slide 4

Gasses in liquidsGasses in liquids• In addition to cold In addition to cold

temperatures, temperatures, high high pressures increase pressures increase solubilitysolubility of gasses of gasses in liquids.in liquids.

• Henry’s LawHenry’s Law::– solubility of a gas in solubility of a gas in

a liquid increases a liquid increases with increasing with increasing pressure of that gas pressure of that gas above the liquid.above the liquid.

Henry's Law.mov

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Bires, 2010 Slide 5

SaturationSaturation• Saturated SolutionSaturated Solution

– solution has as much solute as it will allow solution has as much solute as it will allow

• Unsaturated SolutionUnsaturated Solution– more solute can dissolve into solution more solute can dissolve into solution

• Supersaturated SolutionSupersaturated Solution– too much solute in solution-some will come too much solute in solution-some will come

outout

• We express the We express the quantquantitative amountitative amount of of solute in a solution with solute in a solution with concentrationconcentration … … (later)(later)

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Bires, 2010 Slide 6

Parts of a Parts of a solutionsolution• The The dissolving mediumdissolving medium is the is the

solventsolvent (what does the dissolving… (what does the dissolving…the dissolver)the dissolver)

• The The dissolved substancedissolved substance is the is the solutesolute (what gets dissolved…the (what gets dissolved…the dissolvey)dissolvey)

• The The solute solute andand solventsolvent togethertogether form the form the solutionsolution..

• Solvents and solutes can be any Solvents and solutes can be any phasephase..

solution

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Bires, 2010 Slide 7

Special types of mixtures - Special types of mixtures - SuspensionsSuspensions

• SuspensionsSuspensions– mixtures where the solutes mixtures where the solutes

particles are particles are very largevery large, so they , so they don’t completely dissolvedon’t completely dissolve into into their solvent.their solvent.

• Solute particles will settle out Solute particles will settle out of the solution if left of the solution if left undisturbed. – this creates two undisturbed. – this creates two phaphasesses..

• Muddy water and Italian salad Muddy water and Italian salad dressing are good examples of dressing are good examples of suspensions.suspensions.

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Bires, 2010 Slide 8

Special types of mixtures - Special types of mixtures - ColloidsColloids

• ColloidsColloids– mixtures where the solute particle is mixtures where the solute particle is smaller smaller

than particles in a suspensionthan particles in a suspension, but , but not small not small enough to dissolveenough to dissolve..

• Colloids have two Colloids have two pphhaasseess::• Dispersed phaseDispersed phase – the – the solutesolute• Dispersing mediumDispersing medium – the – the solventsolvent..• Mayonnaise and hair gel are good Mayonnaise and hair gel are good

examples of colloids.examples of colloids.• There are 7 types of colloids, found on There are 7 types of colloids, found on

page 398…page 398…

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Bires, 2010 Slide 10

The Tyndall EffectThe Tyndall Effect• TheThe Tyndall effect Tyndall effect allows us toallows us to distinguish distinguish

between solutions, colloids, and between solutions, colloids, and suspensionssuspensions..

• It works by shining a beam of light into the It works by shining a beam of light into the mixture. If…mixture. If…

• Light is Light is blockedblocked at entry into the mixture at entry into the mixture– the mixture is a the mixture is a suspensionsuspension..

• Light Light passes through unobstructedpasses through unobstructed– the mixture is athe mixture is a solutionsolution..

• Light Light passespasses, but the , but the beam can be seenbeam can be seen in in the mixturethe mixture– the mixture is a the mixture is a colloid.colloid.

John Tyndall, Brittish, c1860

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ElectrolytesElectrolytes• ElectrolytesElectrolytes

– Solutions that Solutions that conduct electricityconduct electricity..

• Ionic solutionsIonic solutions are are electrolyteselectrolytes..

• Covalent solutionsCovalent solutions are are nonelectrolytesnonelectrolytes..

• Is saltwater (NaCl in water) an Is saltwater (NaCl in water) an electrolyte?electrolyte?

• Is sugar water (CIs sugar water (C66HH1212OO66 in water) an in water) an electrolyte?electrolyte?

• Conductivity testerConductivity tester– can tell us if a solution is an electrolyte, and can tell us if a solution is an electrolyte, and

sometimes, how sometimes, how strongstrong an electrolyte is. an electrolyte is.

Electrolytes.mov

)()()( aqaqs ClNaNaCl

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Concentration - Concentration - MolarityMolarity• ConcentrationConcentration

– the the quantitativequantitative amount of solute present in amount of solute present in a solutiona solution

• MolarityMolarity ( (MM) – ) – moles/litermoles/liter– number of moles solute in liters of solutionnumber of moles solute in liters of solution

• We can use the We can use the T-chart methodT-chart method to find to find moles of solute present.moles of solute present.

)(

)()(

Lsolutionofvolume

molsoluteofamountMMolarity

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Try these Molarity exercisesTry these Molarity exercises• What is the concentration [in Molarity] when 3.0 What is the concentration [in Molarity] when 3.0

moles of NaCl are dissolved in 2.0 Liters of moles of NaCl are dissolved in 2.0 Liters of water?water?

• How much (in liters) of a 0.10 M solution do you How much (in liters) of a 0.10 M solution do you need to get 2.0 moles of solute?need to get 2.0 moles of solute?

• How many moles of NaOH are present in 300.mL How many moles of NaOH are present in 300.mL of a 1.0M solution?of a 1.0M solution?

• How many grams of HCl are found in 100mL of a How many grams of HCl are found in 100mL of a 2.0M solution?2.0M solution?

• What mass of NaOH is required to be dissolve in What mass of NaOH is required to be dissolve in 250mL of water to make a 2.8M solution?250mL of water to make a 2.8M solution?

1.5 M “molar”

20 L

.30 moles

7.3 grams

28 g NaOH

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Concentration - Concentration - MolaMolallityity• MolalityMolality ( (mm) – ) – moles/kilogrammoles/kilogram – number of – number of

moles solute in kilogram of moles solute in kilogram of solventsolvent..

• used less often, but important for used less often, but important for colligative propertiescolligative properties

)(

)()(

kgsolventofmass

molsoluteofamountmMolality

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Try these molality exercisesTry these molality exercises• What is the concentration in molality when 2 What is the concentration in molality when 2

moles of NaCl are dissolved in 4kg of water?moles of NaCl are dissolved in 4kg of water?

• How many moles of solute are present in 2 kg How many moles of solute are present in 2 kg of a 3 m solution?of a 3 m solution?

• What mass of alcohol do you need to add to 4 What mass of alcohol do you need to add to 4 moles of benzene to make a 2 m solution?moles of benzene to make a 2 m solution?

• What is the molality of a solution created by What is the molality of a solution created by dissolving 3.50 moles methanol in 340g of CCldissolving 3.50 moles methanol in 340g of CCl44..

• What mass of ethanol (CWhat mass of ethanol (C22HH55OH) is required to OH) is required to add to 4.5 kg of water to create a .86 m add to 4.5 kg of water to create a .86 m solution?solution?

.5 m “molal”

6 moles

2 kilograms

10.3 m

180 g C2H5OH

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Solution PreparationSolution Preparation• By solid dissolving:By solid dissolving:• 1. calculate how many grams are needed to 1. calculate how many grams are needed to

create our volume of our desired molarity create our volume of our desired molarity solutionsolution

• 2. weigh out that mass, and add it to a flask2. weigh out that mass, and add it to a flask

• 3. add some water and allow to dissolve3. add some water and allow to dissolve

• 4. add water to the desired volume4. add water to the desired volume

• By dilution of a standard solution:By dilution of a standard solution:

• 1. use the relationship 1. use the relationship MM11VV11==MM22VV22

• 2. calculate volume of 2. calculate volume of standard molarity solutionstandard molarity solution to use to get desired volume of to use to get desired volume of desired molarity desired molarity solutionsolution.. End of chapter 13…C14 (quant sol) next Dillutions.mov

Solution Prep of CuSO4.mov

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Begin C14Begin C14:: Colligative Properties Colligative Properties• ““ColligativeColligative” means ” means depends on amountdepends on amount..

– property of a solution depends on the property of a solution depends on the amount amount of solute dissolvedof solute dissolved in solution. in solution.

• Physical Properties of a solution change Physical Properties of a solution change because solute particles act as impurities, because solute particles act as impurities, getting in the waygetting in the way of solvent particles. of solvent particles.– lowers freezing pointslowers freezing points– increases boiling pointsincreases boiling points– reduces vapor pressurereduces vapor pressure..

Ethyl glycol is added to water in your car’s radiator to increase water’s boiling point.

The more impurities, the greater the change

Kmt

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OsmosisOsmosis• travel of a solventtravel of a solvent

– from an area of low concentration to high from an area of low concentration to high concentration concentration

– From high purity to low purity.From high purity to low purity.

• Examples of osmosis:Examples of osmosis:– A Cucumber placed in a conc. NaCl solution A Cucumber placed in a conc. NaCl solution

(brine) loses water, shrivels up, and becomes a (brine) loses water, shrivels up, and becomes a pickle.pickle.

– Limp carrots and celery, placed in water, Limp carrots and celery, placed in water, become firm because water enters via osmosis.become firm because water enters via osmosis.

From pure to impure

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DissociationDissociation and Ions Present and Ions Present• DissociationDissociation = a salt dissolving into its = a salt dissolving into its

ions:ions:

• How many moles of ions are in a solution How many moles of ions are in a solution of 1 mole of NaCl?of 1 mole of NaCl?

• How many moles of ions are in solutions How many moles of ions are in solutions of 1 mole of each of the following?:of 1 mole of each of the following?:

)()()( aqaqs ClNaNaCl

24

24 SOCuCuSO

2332 2 CONaCONa

32

23 2)( NOMgNOMg

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Strong/Weak Electrolytes Strong/Weak Electrolytes ReviewReview

• Recall that a solid compound made up of Recall that a solid compound made up of a a cationcation and and anionanion is called a is called a saltsalt..

• SaltsSalts that that dissolve completelydissolve completely into their into their ions when put in water ions when put in water dissociate dissociate completelycompletely..

• Salts that Salts that dissociate completelydissociate completely form form strong electrolytesstrong electrolytes – solutions that – solutions that conduct electricity wellconduct electricity well..

• Some salts only Some salts only partially dissociatepartially dissociate, , forming forming weak electrolytesweak electrolytes – solutions that – solutions that conduct electricity, but do so poorlyconduct electricity, but do so poorly..

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HH++ / / OHOH-- IonsIons – – ((Acids and BasesAcids and Bases))

• When a When a HH++ ion is released into solution, a ion is released into solution, a HH33OO++ ion is produced, called ion is produced, called Hydronium ionHydronium ion..

• When a When a OH-OH- ion is produced, we call this a ion is produced, we call this a Hydroxide ionHydroxide ion..

• AcidsAcids that dissociate completely, that dissociate completely, releasing releasing H+H+ ions form ions form strong electrolytesstrong electrolytes..

• BasesBases that dissociate completely that dissociate completely releasing releasing OH-OH- ions form ions form strong electrolytesstrong electrolytes..

End of chapter 13,(14) – Problem set on next slide

Aqueous Acids (strong and weak).mov

Aqueous Bases (strong and weak).mov

ClHHCl

OHNaNaOH

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Back Bires, 2010 Slide 1 Chapter 13, (14): Mixtures and Aqueous Solutions What are they? Where do we find them? How do we describe them? We use solutions