Download Solutions Part A

SOLUTIONS
Chapter 16
Test Monday 8/09/04
What is a solution?
Any substance – solid, gas, or liquid –
that is evenly dispersed throughout
another substance – solid, gas, or liquid
– is a solution.
Solutions are homogeneous mixtures.
Examples of solutions: Air, 14K gold, sea
water
SOLVENT: The substance that is the
dissolving medium
SOLUTE: The substance dissolved in
the solvent
These are relative terms. The substance
you have more of in a solution is the
solvent. Ex. CH3CH2OH
Structure of water
The process of
Solvation
How can water molecules break the
ionic bonds in a crystal of potassium
permanganate (KMnO4) to dissolve it?
H
H
O
K
H O
Permanganate H
ion
At the surface of the crystal the water
molecules becomes associated with the ions
in the crystal.
A group of water molecules will surround
each ion and isolate it from its neighbors.
These ions are said to be HYDRATED
This process of dissolving a solute in a
solvent is called SOLVATION.
Solvation of a chloride ion
Solvation of the sodium ion
Dissociation
The process of decomposition of a
crystal into hydrated ions is called
DISSOCIATION.
Example
NaCl(s)  Na+(aq) + Cl– (aq)
The symbol (aq) means that the ions
are hydrated.
Molecular Solvation
Solvation can also occur between polar
solute molecules and polar solvent
molecules.
Example: methanol CH3OH.
Is methanol capable or forming a hydrogen
bond?
Solvated molecule of methanol in water
Solvation of Glucose
The polar ends of the solute molecules
are attracted to the oppositely charged
polar regions of the solvent molecules.
In some cases the geometry and
attraction between polar molecules
cause that when two volumes are
added the total volume is less than the
one expected.
Ex. H2O and CH3CH2OH
Miscibility
Two substances are said to be miscible
when there is no limit to the solubility of
one substance into the other
When polar and non-polar substances
are mixed, they show very little
attraction for each other. Solvation does
not occur. Ex: oil and water.
Two liquids that do not mix are called
immiscible
Solutions
Solutions are transparent. You can see
through them.
The mixture remains stable and does
not separate after standing for any
period of time.
The particles are so small they cannot
be separated by normal filtration.
Colloids
Colloids are mixtures with particle sizes that
consist of clumps of molecules. The particles
have dimensions between 2 to 1000
nanometers.
The colloid looks homogeneous to the naked
eye. Fog and milk are examples of colloids.
Colloids frequently appear "murky" or
"opaque". The particles are large enough to
scatter light.
Colloids generally do not separate on
standing. They are not separated by filtration.
Suspensions
Suspensions are mixtures with particles
that have diameters greater than 1000
nm. They are are visible to the naked
eye. Ex: Blood
Suspensions are "murky" or "opaque".
They do not transmit light. Suspensions
separate on standing. The mixture of
particles can be separated by filtration.
Examples of matter in solution
gas in gas: air ( N2, O2 , Ar, CO2 , etc)
gas in liquid: soda pop (CO2 in water)
liquid in liquid: gasoline (hydrocarbons)
solid in liquid: sea water (dissolved salts)
gas in solid: H2 in palladium
liquid in solid: dental amalgams ( Hg in Ag)
solid in solid: alloys ( brass, (Cu/Zn))
GAS-SOLID Solution: Hydrogen dissolved in Palladium
SOLID-SOLID Solution: Alloy
Like dissolves like
Generally two polar molecules are
soluble in each other. Ex. Water and
alcohol.
Many non-polar molecules will dissolve
in non-polar solvents. Ex. Iodine will
dissolve in mineral oil.
The rule of thumb is: like dissolves like
Solubility
SATURATED: A solution that cannot
dissolve any more solute at a given T.
UNSATURATED: A solution that can
dissolve more solute
SOLUBILITY: Is the amount of solute
needed to make a saturated solution at
a given T.
SUPERSATURATED: A solution that
contains more solute that it would
normally holds at a given T.
Solubility is the amount of substance
needed to make a saturated solution at
a given temperature.
It is usually given in grams of the solute
per 100 g of water.
It depends on the solute and solvent.
The word soluble is not a precise term
because solubilities vary greatly. It is
commonly used for solubilities greater
than 0.1 mol per liter of solution.
A saturated solution has the same rate of
precipitation and dissolution
Factors affecting solubility
TEMPERATURE

For many substances solubility increases
with temperature.

The solubility of a gas decreases as the
temperature increases.
Gases are less soluble at high temperatures
Factors affecting solubility
PRESSURE

The solubility of a gas depends on the
pressure.

The higher the pressure the higher the
solubility.
Double the pressure………
Double the concentration
Henry’s Law
How does oxygen partial pressure
affect dissolved oxygen levels?
Oxygen in water obeys Henry's law; the
solubility is roughly proportional to the
partial pressure of oxygen in the air:
pO2 = KO2 xO2
PO2 = partial pressured of the gas
KO2 = Henry constant for water
XO2 = Mole fraction of O2 in a saturated
solution
Ionic Equations
Ionic Equation
Net Ionic Equation
Spectator Ions
Precipitate (ppt)
Which pair forms a precipitate?
KI(aq) + Pb(NO3)2(aq) ----> KNO3 + PbI2
1.
KNO3
2.
PbI2
3.
Neither pair forms a ppt.
Identify the spectator ion(s)
Fe(s) + Cu2+(aq) + SO42-+(aq) Cu(s) + Fe2+(aq) +
SO42-(aq)
1. Cu(s)
2. Cu2+
3. Fe2+
4. SO425. None are spectator ions.
Acid – Base reaction
When an acid and a base react, a salt
and water are formed
Reaction of sodium hydroxide and
hydrochloric acid
NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l)
Base
Acid
Salt
Water
Net Ionic:
OH–(aq) + H+(aq)  H2O(l)
Reaction of a metal and H+ ion
Metals more active than hydrogen react
with H+ ions in solution to form metallic
ions and hydrogen gas.
Reaction of zinc and hydrochloric acid
Zn(s) + 2 HCl(aq)  ZnCl2(s) + H2(g)
Net ionic:
Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g)
Rxn of an acid and a carbonate
When carbonic acid is form in a reaction it
decomposes into CO2 and H2O.
This is an important reaction in living
organisms
Reaction of Na2CO3 and HCl
Na2CO3(aq) + 2HCl(aq)  2NaCl(aq) + H2CO3(aq)
===========
H2CO3(aq)  CO2(g) + H2O(l)