Download Molarity = moles of solute liters of solution M1V1 = M2V2

Solute-Solvent Interaction
Big Idea 2
LO: 8, 9
Introduction: A solution is a mixture of two or more substances in a single phase. At least
two substances must be mixed in order to have a solution. The substance in the smallest
amount and the one that dissolves or disperses is called the SOLUTE. The substance in the
larger amount is called the SOLVENT. In most common instances water is the solvent. The
gases, liquids, or solids dissolved in water are the solutes.
Notes:
This is how solvents and solutes attract. The polar ends align
themselves towards their opposite polarity, surround it and
takes it away…The charge of the polarity (positive/negative)
will define how the molecules/ions align themselves towards
each other and thus interact.
In the above example for the dissociation of table salt (NaCl)
the hydrogen's of water align themselves towards the
negative ion (anion), surround it and takes it away.. If the ion
is a positive ion (a cation) the oxygen of the water align
themselves towards the ion, surround it and takes it away.
Dissolving - The dissolving process involves a consideration of the relative strength of
three intermolecular attractive forces. The type of forces between solute-solute
molecules and solvent-solvent molecules must be considered. These intermolecular
attractions must be broken before new solute-solvent attractive forces can become
effective. Perhaps the bond breaking and bond forming processes take place
simultaneously.
Like Dissolves Like
A solute will dissolve in a solvent if the
solute-solvent forces of attraction are
great enough to overcome the
solute-solute and solvent-solvent
forces of attraction. A solute will not
dissolve if the solute-solvent forces
of attraction are weaker than
individual solute and solvent
intermolecular attractions. Generally,
if all three of the intermolecular
forces of attraction are roughly
equal, the substances will be soluble
in each other.
“Like Dissolves Like” - This means
that ionic or polar solutes dissolve
in polar solvents and non-polar
solutes dissolve in non-polar
solvents. Polar and ionic solutes
DO NOT dissolve in non-polar
solvents and vice versa.
Concentration – Solutions are often referred to as being concentrated or dilute. These two terms are
very general. While concentrated indicates that there is a lot of solute dissolved in the solvent
(perhaps the solution is near to being saturated) and dilute indicates that a small amount of solute
is dissolved in the solvent, we often need to be exact with quantities in chemistry. Molarity (M)
expresses the concentration of a solution in terms of volume. It is the most widely used unit of
concentration, turning up in calculations involving equilibrium, acids and bases, and
electrochemistry, among others.
Note, when you see a chemical symbol in brackets that means they are talking about molarity. For
instance, “[Na+]” is the same as explicitly stating “the molar concentration (molarity) of sodium
ions”.
Molarity = moles of solute
liters of solution
Dilution - The process of taking a more concentrated solution and adding water to make it less
concentrated. The more concentrated solution before the dilution is performed is known as
the stock solution. You can relate the concentration of the stock solution to the concentration of
the diluted solution using the equation below:
M1V1 = M2V2
Where M is molarity and V is the volume, in liters, of the solution
Remember that when applying the solubility rule:
"Likes Dissolve Likes", that there are no absolutes
and there are exceptions with a small amount of
solubility possible. The rule is most useful when
making comparisons between a series of
compounds.
Affecting Solubility
There are three main factors that control solubility of a
solute.
(1) Temperature
(2) Nature of solute or solvent
(3) Pressure
EFFECT OF TEMPERATURE - Generally in many
cases solubility increases with the rise in temperature
and decreases with the fall of temperature but it is
not necessary in all cases. However we must follow
two behaviors:
-In endothermic process solubility increases with
the increase in temperature and vice versa.
-i.e. solubility of potassium nitrate increases with
the increase in temperature.
-In exothermic process solubility decrease with the
increase in temperature.
-i.e. solubility of calcium oxide decreases with the
increase in temperature.
-Gases are more soluble in cold solvent than in
hot solvent.
NATURE OF SOLUTE AND SOLVENT - Solubility of
a solute in a solvent purely depends on the nature of
both solute and solvent.
-“Like dissolves like”
EFFECT OF PRESSURE - The effect of pressure is
observed only in the case of gases.
-An increase in pressure increases of solubility
of a gas in a liquid.