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Factors Affectingsolubility

Mr. Shields Regents Chemistry U12 L06

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We learned there are 3 things that affect the RATE solids dissolve in liquids.

1)Temperature2) Surface area3) Stirring

It turns out that there are also 3 things that canAffect how much solute will dissolve in a solvent

1) The Nature of solute & solvent2) The Temperature3)The Pressure (when dealing w/gases)

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The Nature of ThingsThe Nature of ThingsWhen we talk about the NATURE of solute & solventwe are referring to their similarities in Polarity

In other words are the solute and solvent…

a) molecules (if so are they non-polar or polar) b) ionic

For example, how would you classify the following:

H20 CCL4 CHCl3CH3CH2OH Br2 NH4NO3Ca(OH)2 KI

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The Nature of ThingsThe Nature of Things

- polar solvents will dissolve polar solutes - non-polar solvents will dissolve non-polar solutesBUT - In general ONLY water will dissolve Ionic compounds In other words …

the principal of “LIKE DISSOLVES LIKE”

Compounds that are of similar polarity will in generalBe soluble in one another. So…

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Solubility TableSolubility TablePolarPolar Non-Non-

PolarPolarEthanolEthanol

PolarPolar SS NSNS SS

Non-Non-PolarPolar

NSNS SS SS

IonicIonic SS NSNS NSNS

Since it’s polar why don’t we just classify it under Polar?

Well, it has something to do with the ends of this molecule.

Hey! What’s with theEthanol?

This molecule is Polarbut it dissolvesNon-polar solutes!

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EthanolEthanolEthanol as a solvent has Unique properties. It behaves Like BOTH a polar and Non-polar solvent.

How does it do this? Ethanol, and solvents like it, haveboth polar and non-polar regions within the molecule

CH3CH2-OH

Non-polar endPolar end

Due to this duality the molecule is able to dissolve bothPolar and non-polar covalent solutes BUT NOT IONIC SALTS

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TemperatureTemperatureWhen we consider the effect of temperature on Solubility we need to ask two questions:

1) Are we dissolving a solid in a liquid

2) Are we dissolving a gas in a liquid?

This is important because …The solubility of gases in liquids dec. with inc. temp. and …

The solubility of solids in liquids (in general) inc. with inc. temp

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Gases & TemperatureGases & TemperatureLet’s consider gases in liquids first…

It is important to recognize that for most gases their Solubility in WATER is typically very low.

- At RT only 8mg of O2 will dissolve in 1000g H20

Consider a glass of soda

You pour it while sitting outside on a warm sunny day. The soda is at first very bubbly and refreshing but

after awhile it becomes “flat”. Why?

Because the solubility of CO2 (g) decreases as the sodaWarms up, and the excess gas leaves the liquid (as bubbles).

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This relationship is true for all gases –

As temperature goes up

Inc

RT

ICE/WATER

- solubility of O2 at 0 deg C = 15mg /1000g H20

- solubility of O2 at 25 deg C = 8 mg /1000g H20

solubility goes down

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Gas Solubility Gas Solubility Some gases like CO2 have a higher solubility than other gasesBecause they can interact with water in a reversible reaction

CO2 + H2O H2CO3

Non-polar

Non-polar

Room Temp

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SO… gas solubility decreases with increasing temperatureBut why is this?

As temperature increases so does KE and thus so does Molecular Velocity

Molecules of gas moving at higherVelocities can escape the intermolecular Force of Attraction between them &the Liquid more easily

It has to do with the KE of the dissolved gas molecule

KE = ½ mv2

As KE inc. Molecular Velocity Increases

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Total gas dissolvedTotal gas dissolvedOne last point. The total amount of dissolved gas is simplythe sum of the Solubility of allThe gases present.

Which means… theSolubility of eachGas Is independent Of the presence ofOther gases.

+

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Solubility Of SolidsSolubility Of SolidsTable G in your reference table shows what the solubilityOf several solids and gases is as a function of temperature. These represent “saturation” curves

What does the x and Y axisTell us?

What is the solubility of KNO3At 50 deg C?

83g/100g H2O

What is the solubility of KCl in200g of water at 50 deg. C?

84g

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Solubility CurvesSolubility CurvesUsing Table G …

What gases are represented?SO2, NH3, HCl

Which solute is least affectedBy temperature change?

NaClWhich solute is most affectedBy temperature change?

KNO3Which compound is least solubleat 20 deg. C?

KClO3Which compound is most soluble at 20 deg. C?

KI

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Problem: If 100g of water at 100 deg C can dissolve 165g of NaNO3, how many grams of NaNO3 precipitate from solution (i.e. crystallize) as the solution is chilled to 20 deg. C?

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Predicting SolubilityPredicting Solubility

Table F in the reference tables handbook will help you toPredict the solubility of an ionic compound.

Notice the table is divided into two sections:

- Ions that form Soluble Compounds

- Ions that form Insoluble Compounds

IMPORTANT: Each section lists EXCEPTIONS to the rule

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Predicting SolubilityPredicting SolubilityTable F in the reference tables handbook will help you toPredict the solubility of an ionic compound.

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Solubility ProblemPredict the solubility of the following compounds:

Ca(NO3)2Rb2SNi(OH)2AgClAl2(SO4)3BaSO4LiOH(NH4)2CrO4CaHCO3

SolSolInsol.Insol.Sol.Insol.Sol.Sol.Sol.

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Predicting SolubilityPredicting Solubility

Though you can refer to Table F you might want toRemember a few rules such as the following:

ALL COMPOUNDS OF GROUP 1 METALS ARE SOLUBLE

ALL AMMONIUM COMPOUNDS and ALL NITRATES ARE SOLUABLE

Li+ Na+ K+ Rb+ Cs+ Fr+

NH4 + NO3 -

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Effect of PressureEffect of Pressure

2 rules regarding pressure…

1) Pressure HAS NO EFFECT on the solubility of solidsin liquids or liquids in liquids

AND …

2) Pressure has a BIG EFFECT on the solubility of a gasin a liquid.

For example … Consider what happens when you open a bottle of warm soda

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Why does soda FIZZOr the Can “POP” when opened?

Popping the top releasesThe pressure …

So what happens to theSolubility of the gas inThe liquid?

Pressure allows more gas to dissolve in the liquid.

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Henry’s LawHenry’s Law

The amount of a gas dissolved in a solution (C) isThe amount of a gas dissolved in a solution (C) is directlydirectly

proportionalproportional to the pressure of the gas (P) above the solution.to the pressure of the gas (P) above the solution.

C1 = C2P1 P2

In other words, if P doubles

then the concentration of the Gas doubles

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Solubility of a gas Problem; Henry’s Law at work:

C1 = C2P1 P2

P1 P2

C1 = 9.5

C2 = 38 g/100ml9.5 = C22 8

If the initial pressure of a gas over a liquid is 2 atm. and theSolubility of the gas is 9.5 mg per 100g of water what is theSolubility of the gas if the pressure of the gas is increased To 8 atm.