Factors Affecting
solubility
Mr. Shields
Regents Chemistry
U12 L06
1
We learned there are 3 things that affect the
RATE solids dissolve in liquids.
1) Temperature
2) Surface area
3) Stirring
It turns out that there are also 3 things that can
Affect how much solute will dissolve in a solvent
1) The Nature of solute & solvent
2) The Temperature
3)The Pressure (when dealing w/gases)
2
The Nature of Things
When we talk about the NATURE of solute & solvent
we 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
CH3CH2OH
Ca(OH)2
CCL4
Br2
KI
CHCl3
NH4NO3
3
The Nature of Things
Compounds that are of similar polarity will in general
Be soluble in one another. So…
- polar solvents will dissolve polar solutes
- non-polar solvents will dissolve non-polar solutes
BUT
- In general ONLY water will dissolve Ionic
compounds
In other words …
the principal of “LIKE DISSOLVES LIKE”
4
Solubility Table
Hey! What’s with the
Ethanol?
This molecule is Polar
but it dissolves
Non-polar solutes!
Polar
NonPolar
Ethanol
Polar
S
NS
S
NonPolar
NS
S
S
Ionic
S
NS
NS
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.
5
Ethanol
Ethanol 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, have
both polar and non-polar regions within the molecule
CH3CH2-OH
Non-polar end
Polar end
Due to this duality the molecule is able to dissolve both
Polar and non-polar covalent solutes BUT NOT IONIC
6
SALTS
Temperature
When 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
7
Gases & Temperature
Let’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 soda
Warms up, and the excess gas leaves the liquid (as bubbles).8
This relationship is true for all gases –
As temperature goes up solubility goes down
RT
ICE/WATER
Inc 
- solubility of O2 at 0 deg C = 15mg /1000g H20
- solubility of O2 at 25 deg C = 8 mg /1000g H20
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Gas Solubility
Some gases like CO2 have a higher solubility than other gases
Because they can interact with water in a reversible reaction
CO2 + H2O  H2CO3
Room Temp
Non-polar
Non-polar
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SO… gas solubility decreases with increasing temperature
But why is this?
It has to do with the KE of the dissolved gas molecule
As temperature increases so does KE and thus so does
Molecular Velocity
KE = ½ mv2
Molecules of gas moving at higher
Velocities can escape the intermolecular
Force of Attraction between them &
the Liquid more easily
As KE inc. Molecular
Velocity Increases
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Total gas dissolved
One last point. The total amount of dissolved gas is simply
the sum of the
Solubility of all
The gases present.
Which means… the
Solubility of each
Gas Is independent
Of the presence of
Other gases.
+
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Solubility Of Solids
Table G in your reference table shows what the solubility
Of several solids and gases is as a function of temperature.
These represent “saturation” curves
What does the x and Y axis
Tell us?
What is the solubility of KNO3
At 50 deg C?
83g/100g H2O
What is the solubility of KCl in
200g of water at 50 deg. C?
84g
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Solubility Curves
Using Table G …
What gases are represented?
SO2, NH3, HCl
Which solute is least affected
By temperature change?
NaCl
Which solute is most affected
By temperature change?
KNO3
Which compound is least soluble
at 20 deg. C?
KClO3
Which compound is most soluble at 20 deg. C?
KI
14
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?
15
Predicting Solubility
Table F in the reference tables handbook will help you to
Predict 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 Solubility
Table F in the reference tables handbook will help you to
Predict the solubility of an ionic compound.
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Solubility Problem
Predict the solubility of the following compounds:
Ca(NO3)2
Rb2S
Ni(OH)2
AgCl
Al2(SO4)3
BaSO4
LiOH
(NH4)2CrO4
CaHCO3
Sol
Sol
Insol.
Insol.
Sol.
Insol.
Sol.
Sol.
Sol.
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Predicting Solubility
Though you can refer to Table F you might want to
Remember a few rules such as the following:
ALL COMPOUNDS OF GROUP 1 METALS ARE SOLUBLE
Li+ Na+ K+ Rb+ Cs+ Fr+
ALL AMMONIUM COMPOUNDS and ALL NITRATES ARE SOLUABLE
NH4 +
NO3 -
19
Effect of Pressure
2 rules regarding pressure…
1) Pressure HAS NO EFFECT on the solubility of solids
in liquids or liquids in liquids
AND …
2) Pressure has a BIG EFFECT on the solubility of a gas
in a liquid.
For example … Consider what happens when you open a
bottle of warm soda
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Why does soda FIZZ
Or the Can “POP” when
opened?
Pressure allows more gas
to dissolve in the liquid.
Popping the top releases
The pressure …
So what happens to the
Solubility of the gas in
The liquid?
21
Henry’s Law
The amount of a gas dissolved in a solution (C) is directly
proportional to the pressure of the gas (P) above the solution.
C1 = C2
P1
P2
In other words, if P doubles
then the concentration of the Gas doubles
22
Solubility of a gas Problem; Henry’s Law at work:
If the initial pressure of a gas over a liquid is 2 atm. and the
Solubility of the gas is 9.5 mg per 100g of water what is the
Solubility of the gas if the pressure of the gas is increased
To 8 atm.
C1 = C2
P1
P2
C2 = 38 g/100ml
9.5 = C2
2
8
C1 = 9.5
P1
P2
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