Factors Affecting

1
SOLUTIONS
Factors Affecting solubility
Mr. Shields Regents Chemistry U12 L06
2
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)
3
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 CCL4 CHCl3 CH3CH2OH Br2 NH4NO3 Ca(OH
)2 KI
4
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
5
Solubility Table
Polar Non-Polar Ethanol
Polar S NS S
Non-Polar NS S S
Ionic S NS NS
Hey! Whats with the Ethanol? This molecule is
Polar but it dissolves Non-polar solutes!
Since its polar why dont we just classify it
under Polar? Well, it has something to do with
the ends of this molecule.
6
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
Due to this duality the molecule is able to
dissolve both Polar and non-polar covalent
solutes BUT NOT IONIC SALTS
7
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
8
Gases Temperature
Lets 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).
9
This relationship is true for all gases As
temperature goes up
solubility goes down

• solubility of O2 at 0 deg C 15mg /1000g H20
• - solubility of O2 at 25 deg C 8 mg /1000g H20

10
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
11
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 Molecules of gas
moving at higher Velocities can escape the
intermolecular Force of Attraction between them
the Liquid more easily
KE ½ mv2
12
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.

13
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
14
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
15
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?
16
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
17
Predicting Solubility
Table F in the reference tables handbook will
help you to Predict the solubility of an ionic
compound.
18
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.
19
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 ALL AMMONIUM COMPOUNDS and ALL
NITRATES ARE SOLUABLE
Li Na K Rb Cs Fr
NH4 NO3 -
20
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
21
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?
22
Henrys 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
23
Solubility of a gas Problem Henrys 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.