Post on 03-Feb-2022
Unit 11: Solutions
H2O
Good solvent
High Surface tension
Low vapor pressure
High boiling point
WHAT PROPERTIES OF
WATER MAKE IT ESSENTIAL
TO LIFE OF EARTH?
Water is a polar
molecule. It
experiences
hydrogen bonding
due to its polar
nature.
After many hydrogen bonds are formed, you have a weak force holding all the water molecules to each other.
Hydrogen bonding is
the reason water freezes
into ice crystals of a
certain repeating shape
(hexagons)
Volume increases.
Hydrogen bonding is what gives proteins and
nucleic acids their three dimensional shape.
Hydrogen bonding also causes water
to have….
High Surface Tension (cohesion)
Surfactant
Surface Tension can be
decreased by adding a
surfactant – this type of
substance interferes
with hydrogen bonding.
Surfactants are used in
soaps, detergents,
paints, adhesives,
inks…
Hydrogen bonds also cause water to
have…
A high boiling point and a low vapor
pressure.
Water is also
attracted to other
substances like
glass.
Water can be drawn up into a thin
glass tube with no effort (capillary
action) because of the attraction
between the water and glass
molecules.
Matter
Pure Substances
Mixtures
Elements Compounds Heterogeneous Mixtures
Homogeneous Mixtures
Classification of Matter
anything composed of atoms
Two types of mixtures!
Heterogeneous Mixtures
Two or more pure substances mixed
unevenly (you can see the different
components).
Example: fruit salad, pizza, granite
Suspensions
A suspension is a heterogeneous
mixture that has large particles that will
stay suspended as long as the mixture
is in motion
Once the motion stops, the particles
will fall to the bottom or settle out
Can be separated through filtering
Colloids
Homogeneous mixtures where the
medium sized particles are
dispersed throughout but are not
heavy enough to settle out.
Appear cloudy and opaque
Cannot be separated by filtering
Can be separated by a centrifuge
How can light be used to tell the difference
between colloids and solutions?
Tyndall effect
A beam of light passing through a solution, such as air, is not visible.
Light passing through a colloid, such as fog, will be scattered by the larger particles and the light beam will be visible.
Homogeneous Mixtures
Two or more pure substances mixed evenly.
When you look at it, you can’t see separate
parts.
– Also called solutions (can be liquid, gas or
solid solutions)
Examples: salt water, soda, coffee,
Parts of a solution
Solute – the substance being dissolved.
Solvent – the substance that is doing the dissolving (usually present in a greater amount).
Solvent
Solute
The solute dissolves INTO
THE solvent to form a
solution.
Miscible – two
substances that will mix
and dissolve together in
any proportion
Immiscible – two
substances that are
insoluble in one another.
Water and oil are
_______________.
Factors that affect the rate of dissolution
Temperature
– Dissolve faster at higher temp
Agitation
– Dissolve faster when the mixture is shaken or stirred.
Surface Area
– Dissolve faster if you increase their surface area
(broken up into smaller pieces)
VS.
Solubility in Water :
The simple rule to remember is ‘like dissolves like’
+
-
+
Water is a polar solvent and will dissolve polar
molecules and substances that contain
charged particles.
Substances that dissolve in H2O are said to be soluble
• Ex: Sugar, ethanol (type of alcohol) which are polar,
most ionic compounds
sucrose
Site of polarity can
form H-bonding
When solid sodium
chloride (NaCl)
dissolves in water it
breaks up into its
individual ions.
Water is polar, the different ends are attracted to the charged ions.
The positive and negative ions become surrounded by solvent-
solvation.
-
+
+
Cl-
Na+
Electrolytic Solutions
Ionic Compounds dissociate in
aqueous solutions and create
positive and negative ions in
solution. Their ability to move
nearly independently through the
solution permits them to carry
positive or negative electrical
charges from one place to
another. Hence the solution
conducts an electrical current
and are called electrolytes.
Electrolytic Solvation
Strong
Electrolyte
Non-
Electrolyte
solute exists as
ions only
- +
salt
- +
sugar
solute exists as
molecules
only
- +
acetic acid
Weak
Electrolyte
solute exists as
ions and
molecules
Electrolytic Solvation
Strong
Electrolyte
Non-
Electrolyte
ionic
compounds/
strong acids
and bases
- +
salt
- +
sugar
covalent
compounds
- +
acetic acid
Weak
Electrolyte
weak acids and
bases
Solution 1 Solution 2 Solution 3 Solution 4 Solution 5
Which beakers contain an electrolytic solution:
KCl
Solution
HNO3
Solution
Sugar
Solution
Acetic
Solution
Ammonia
Solution
Substances that don’t dissolve are called insoluble
E.g. Petroleum (crude oil), which are non-polar
So if you want to dissolve grease which is non-polar, you
need to use a non-polar solvent.
Petroleum in a non-polar organic molecule
How is solubility of a compound denoted in a
chemical equation?
, yields
How do we know if
the products of a
chemical reaction
are (aq), a solution
or (s), a
suspension or a
precipitate?
AB + CD AD + CBWhich of the products produced will be soluble?
Double Replacement
Reactions
• potassium iodide + lead (II) nitrate
• barium nitrate + calcium carbonate
Saturation
MAXIMUM Amount of solute dissolved
Saturation – The
point when no more
solute can dissolve
into a solvent at a
given temperature ( a
dynamic equilibrium
exists between the
solution and
undissolved solute).
Unsaturated Solution
An unsaturated
solution is like a
sponge that can hold
more water.
More solute can be
dissolved at that
temperature.
I’m still
thirsty!
Supersaturated Solution
Can be prepared by
changing the conditions
of a saturated solution
(temperature, volume,
or pressure).
A supersaturated solution is a solution that contains more of the solute than it can normally hold at a given temperature.
Solubility
SATURATED
SOLUTION
no more solute
dissolves
UNSATURATED
SOLUTION
more solute
dissolves
SUPERSATURATED
SOLUTION
becomes unstable,
crystals form
concentration
SOLVATION & SOLUBILITY
CURVES
Solubility
Solubility Curve
– shows the
dependence of
solubility on
temperature
Solubility Curve
Most solubility curves
show the solubility of
more than one solute.
These graphs show
comparisons.
Which solute is most
soluble at 100˚C?
KNO3 is most soluble at
100 degrees.
Practice:
What is the solubility of
KBr at 80ºC?
Which salt is the most
soluble at 50ºC?
At which temperature
can you dissolve 160 g
of KNO3 in 100 g of
water?
Unsaturated, Saturated, and Supersaturated
solution
Solutions that are described by the line are always
SATURATED SOLUTIONS.Solutions that are above the line are always
SUPERSATURATED SOLUTIONS.
Solutions that are below the line are always
UNSATURATED SOLUTIONS.
Practice:
How many grams of
sodium chloride can be
dissolved in 100 g of
water at 80ºC?
If 40 g of potassium
bromide is dissolved in
100 g of water at 80ºC, is
the solution saturated,
unsaturated, or
supersaturated?
Solubility Curve What if we change the amount of water?
In order to reach saturation, if we double the
amount of water that is being used to prepare
the solution, we would need to also double the
solute.
20 g / 100g of water at 25 °C
40 g / 200g of water at 25 °C
Example:
How many grams of
KBr would be needed to
saturate 50g of water at
90°C?
It takes 100g of KBr to
saturate 100g of water,
so it would take 50g of KBr
to saturate 50g of water.
What do you notice
about the
relationship between
temperature and
solubility of solids
and gases in water?
Generally, as temperature
increases, the solubility of solids
increase.
As the temperature
increases, the
solubility of a gas
decreases.
Why?
Solubility and Temperature
Increased temperature causes an increase in
kinetic energy.
The higher kinetic energy causes more motion in
molecules which break intermolecular bonds and
escape from solution.
The solubility of gases decreases as the
temperature increases.
• Ex: room temp soda tastes more “flat” than cold
soda
Solubility of gases and
temperature
Gas pressure and
solubility
Gases increase in
solubility as pressure
increases (Henry’s law)
The gas molecules are
"forced" into the
solution since this will
best relieve the pressure
http://www.youtube.com/watch?v=8yU5y-cFXoo
Problems
A solution is prepared
with 10g of NaCl at
120°C. What type of
solution is it?
A. Unsaturated
B. Saturated
C. Supersaturated
D. Heterogeneous
Problems
How many grams of
KBr are needed to
saturate 100g of water
at 90°C?
A. 80g
B. 90g
C. 100g
D. 110g
Problems
How many grams of
KBr are needed to
saturate 200g of water
at 90°C?
A. 160g
B. 180g
C. 200g
D. 220g
CONCETRATIONS &
DILUTIONS
Concentration
Measure of how much solute is dissolved in solution, or “strength”
of solution.
– Concentrated: A solution with a relatively high
concentration of solute
• strong coffee
– Dilute: very little solute in the solution
• weak coffee
These statements are vague so lets get more specific…..
Concentration
Molarity(M) – is used by chemist to
describe concentrations. It’s a measure
of how many moles of solute are present
for each liter of solution.
A 9M solutions is more concentrated
than a 3M solutions.
solution of L
solute of moles(M)molarity
• Suppose you have 2.00 moles of
sugar and you mix it with enough
water to make 1.00 liter of solution-
what is the molarity of the solution?
• 2M or “two molar”
Practice
• Find the molarity of a solution containing 75 g
of MgCl2 in 250 mL of water.
L
molM Given:
Mass = 75g
Volume = 250 mL
Unknown:
M=?
Practice
• How many grams of NaCl are required to make
a 1.54M solution using 0.500 L of water?
L
molM Given:
Molarity= 1.54 M
Volume = 0.500L
Unknown:
mass=?
Other ways to express
concentration…• Molality (m)
– Concentration calculated by dividing the
moles of solute by the kilograms of solvent
(usually water) used to dissolve.
m=mols solute/kg solvent
Suppose you dissolve 18.2 grams of sucrose
(C12H22O11) into 200. grams of water. What is
the molality of the solution?
Other ways to express
concentration…• Mole fraction (X)
X= moles of component/total moles of all components
• You mix 1.7 moles of sodium chloride with 6.7 moles of
water. What is the mole fraction of the sodium chloride?
Other ways to express
concentration…• Percent (%) mass
% mass = grams of component/total mass of mixture
• 16 grams of NaBr are mixed with 32 grams of
water. What is the % mass of sodium bromide?
2211 VMVM
Dilution
Preparation of a desired solution by adding
water to a concentrate.
Moles of solute remain the same.
What volume of 15.8M HNO3 is required to
make 250 mL of a 6.0M solution?
Practice
How much 0.05 M
HCl solution can
be made by
diluting 250 mL of
10 M HCl?
How much water
would I need to
add to 500 mL of
a 2.4 M KCl
solution to make
a 1.0 M solution?