lecture 7.5 - solutions & solubility

8/14/2019 Lecture 7.5 - Solutions & Solubility

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States Of Matter IV:States Of Matter IV:

Solutions & SolubilitySolutions & Solubility


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yy

NaCl Dissolving in Water

2nexthttp://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.sw


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A saturated solution contains the maximum amount of a

solute that will dissolve in a given solvent at a specific

temperature.

An unsaturated solution contains less solute than thesolvent has the capacity to dissolve at a specific

temperature.

A supersaturated solutioncontains more dissolved solutethan will ordinarily dissolve at a specific temperature.

Sodium acetate crystals rapidly form when a seed crystal is

added to a supersaturated solution of sodium acetate.

3


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Super Saturated Sodium Acetate

next4


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Factors Affecting Solubility

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1.Structure

2.Temperature

3.Pressure

Solubility - the maximum amount of solute than can

dissolve in 100 g of solvent at a given temperature.


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Structure

Attractivity

Solubility increases as attractivitybetween solvent and solute increases

Accessibility

Larger molecules w/ fewer attractivesites are less soluble (solvent lessable to isolate and surround largersolutes)

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Methanol vs ButanolMethanol vs Butanol

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Attractive sitesAttractive sites

(Hydrogen Bonding)(Hydrogen Bonding)

Unattractive SitesUnattractive Sites

(nonpolar)(nonpolar)

Methanol molecules are small enough to be completely

surrounded by water (and form hydration cells)

As the ease of a solvent to isolate solute molecules decreases,

solubility decreases


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Glucose: High Solubility Due To StructureGlucose: High Solubility Due To Structure

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Hydrogen bonding site

Glucose and other

sugars have many

attractive sites for polar

solvent interaction


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More Examples

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11

The Cleansing Action of Soap

Some dissolution processes are quite complex and depend on

different sides of a molecule doing different things.

Ex: Soap with grease


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Temperature

For liquids and solidssolubility generallyincreases as temperature increases.

For gases, solubility decreases astemperature increases.

Solubility can be displayed as solubility curves

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Temperature and Solubility: Solids

olid solubility and temperature

solubility increaseswith increasingtemperaturesolubility decreases

with increasingtemperature

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Reading Solubility Curves

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supersaturated

unsaturated

Saturated Solution(ratedissolution = rate deposition )

Q: 65 g of KNO3 is dissolved

in 100g of H2O at 60C.

a)How many g of KNO3 can

be dissolved to make asaturated solution?

b)How many g of KNO3 will

precipitate when solution is

cooled to 20C?


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Suppose you have 90 gKNO3 contaminated with

10 g NaCl.Fractional crystallization:

1. Dissolve sample in 100mL of water at 600C

2. Cool solution to 00C

3. All NaCl will stay in

solution (s = 34.2g/100g)4. 78 g of PURE KNO3 will

precipitate (s = 12g/100g). 90 g 12 g =78 g

Fractional crystallization is the separation of a

mixture of substances into pure components on

the basis of their differing solubilities.

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Temperature and Solubility: Gases

2 gas solubility and temperature

solubilityusuallydecreaseswithincreasing 16


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Pressure

Pressure has very little effect on the solubility of

liquids and solids.

Pressure is very important to the solubility of

gases however.

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Henrys LawThe solubility of a gas is directly proportional to its

partial pressure above the solution.

kPC=

Applies most accurately for dilute

solutions of gases that do not

dissociate or react with thesolvent

Yes CO2, N2, O2

No HCl, HI19

William Henry

1775 1836
http://upload.wikimedia.org/wikipedia/commons/e/ef/William_Henry.jpg


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Henrys Law

The solubility of a gas in a liquid is proportionalto the pressure of the gas over the solution.

c = kPc is the concentration (M) of the dissolved

P is the pressure of the gas over the solutio

k is a constant for each gas (mol/Lat

that depends only on temperature

low P

low c

high P

high c

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Henrys Law Sample Problem

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The solubility of pure N2 (g) at 25oC

and 1.00 atm pressure is 6.8 x 10-4

mol/L. What is the solubility of N2under atmospheric conditions if thepartial pressure of N2 is 0.78 atm?


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The solubility of pure N2 (g) at 25oC and 1.00 atm

pressure is 6.8 x 10-4 mol/L. What is the solubilityof N2 under atmospheric conditions if the partial

pressure of N2 is 0.78 atm?

Rearrange Henrys law to

2

2

1

1

P

solubility

P

solubility

constantaPressure

solubility

k====

and plug in the valuesSolubility1 = 6.8x10

-4mol/L P1 = 1.00 atm

Solubility2 = P2 = 0.78 atm

LmolS

atm

S

atm

Lmol

/103.5

78.000.1

/108.6

4

2

2

4

=

=

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Factors that Affect Dissolving Rate

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Any factor that can increase the solvents ability tointeract and isolate solute will increase dissolving rate

1.Temperature

2.Stirring & Agitation

3.Surface Area


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NaCl Dissolving in Water

24nexthttp://www.learnerstv.com/animation/chemistry/molvie1.swf


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Temperature & Rate

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As temp. increases, solvent movesfaster

- collision frequency w/ solute

increases- force of collision w/ solute increase

A i i & R


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Agitation & Rate

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Stirring moves

solvent-solutecomplexes away fromsolute surface

- fresh solute surfaceis continually exposedto fresh solvent


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Surface Area & Rate

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Increasing surface area of solute increases the

probability of solvent-solute collision/interaction grinding (pulverizing) the solute into smaller size

particles

Smaller particles have moresurface area than larger size

particles. Since dissolving occurs at

the surface of the solute, this allows

more solvent to come in contact

with more solute.

N l ti Di t C k & M t


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Nucleation - Diet Coke & Mentos

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Chemistry In Action: Scuba Diving


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Chemistry In Action: The Killer LakeLake Nyos, West AfricaLake Nyos, West Africa

8/21/19868/21/1986COCO22 Cloud ReleasedCloud Released

1700 Casualties1700 Casualties

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http://upload.wikimedia.org/wikipedia/en/e/e7/Limnic_degassing1.jpg


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Homework

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p. 550 # 57, 60


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Announcements

Get handouts from Unit 6 Nuclear Chem folder LAB QUIZ #5 (Labs 10, 12, 13) on Wed 1/6/10

RXN Quiz #5 (includes COMPLEXATION rxns) onFri 1/8/10

No complex ion nomenclature tested!

FINAL EXAM 1/14/10 or 1/15/10

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lecture 7.5 - solutions & solubility

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