Transcript Unit 8
Solutions and
Solubility
Essential Questions
1. What’s a solution vs mixture?
2. What’s the difference between a solution,
solvent and solute?
3. Can do you quantify concentration?
4. What do some things dissolve while
others do not?
5. How can we increase the rate that
something dissolves?
What happens when stuff dissolves?
http://www.youtube.com/watch?v=0cPFx0
wFuVs
Mixtures and Solutions
Remember back to the beginning of the
year when we learned about mixtures!
Concept check: Identifying Mixtures
Identify the follow as homo or heterogenous:
Milk
Oil
Muddy water
Iron
Brass
Blood
Paint
Water
Soda
Sugar water
Flat Soda
Toothpaste
Heterogeneous Mixtures
There are two types of heterogeneous
solutions:
Suspensions: mixtures containing particles that
will settle out if left undisturbed.
Examples: oil and water, sandy water, muddy water,
paint, and flour in water
Colloids: mixtures of smaller sized particles that
do not settle out on their own
Examples: milk, blood, butter, smoke, spray
deodorant, motor oil
Homogenous Mixtures
Also called solutions
Can be solids, liquids or gases
Single phase
Remain mixed; particles DO NOT settle out
Cannot be separated by filter paper
Solutions
A solution is formed when a solute
dissolves in a solvent forming a
homogeneous mixture
Solutions
Solvent – present in the greatest
amount
Solute – present in the lesser amount
Solution – Mixture of 2 or more
substances that are a mixed
homogeneously
Identify the solvent and solute?
Solution
Flat Soda
Solvent
Water
Solute
Sugar syrup
Lemonade
Water
Lemonade mix
Alloy like brass
Copper
Zinc
Air
Nitrogen
Oxygen
Antifreeze
Water
Antifreeze
Ocean Water
Water
salt
Antifreeze Close up
In 1885 Karl Benz of Germany invited the
first radiator for cars
Before this, car engines were cooled with
water and needed to be constantly refilled!
Antifreeze has ethylene glycol added to
water to
elevate the boiling point and
depress the freezing point
Solvent Joke
WATER AS A SOLVENT
Water is the most effective solvent
Water will dissolve many ionic
compounds and most polar covalent
compounds
Water is not effective as a solvent for
non-polar covalent compounds
Effectiveness of water is because water
is highly polar with hydrogen bonds
WATER AS A SOLVENT-HYDROGEN
BONDING
The bond formed between an
oxygen atom from one water
molecule and a hydrogen atom
from another water molecule
Image used courtesy of CINCH ® Learning
Polarity Demonstration
Image used courtesy of: http://www.glogster.com/arooke2/hydrogen-bonds/g6m99vd692fc7hgidt985ta0?old_view=True
Concentration
The concentration of a solution is usually
described as concentrated or dilute
There are many
ways to express
concentration:
Concentration as Percent by Mass
Ratio of the solutes mass to the mass of the
solution expressed as a percentage!
Amount of solution = solute + solvent
percent by mass = amount of solute x 100
amount of solution
Concentration as percent by mass
1) What is the percent by mass if 2 grams
of sugar is added and dissolved in 10
grams of water?
16.7%
Concentration as percent by mass
2) In order to maintain a sodium chloride
(NaCl) concentration similar to ocean
water, an aquarium must contain 3.6 g
NaCl per 100.0 g of water. What is the
percent by mass of NaCl in the solution?
3.5%
Concentration as MOLARITY
Another common unit of concentration used
by chemist is molarity
Molarity = the solutions concentration
measured as moles of solute per liter of
solution
Molarity = Moles of solute
Liters of solution
Units of M = Moles / Liter
Concentration as Molarity
1) How much sucrose, in moles, is there in
0.5 liters of a 2-molar (2M) solution?
1 mole
Concentration as Molarity
2) To make a 4.0 M solution, how many
moles of solute will be needed if 12 L of
solution are required?
Concentration as Molarity
3) 116.88 grams of NaCl are dissolved in 1.5
liters of solution. What is the molarity of
this solution?
First, convert grams of NaCl to moles NaCl
Found by dividing 116.88g by the molar mass of NaCl,
58.44 g/mol
116.88g NaCl is 2.00 moles of NaCl
Next, divide moles solute by liters of solution
2.00 moles NaCl = 1.33 mol NaCl/L = 1.33 M NaCl
1.5 L
Practice
Try the following calculating concentration
as percent by mass and molarity problems
Dilution
What does it mean to dilute a solution?
Dilution
In the lab, sometimes reactions call for
different strengths or concentration of
solutions in order for a reaction to occur.
We use molarity to create solutions with
the proper concentrations.
Often we need to dilute a stronger solution
to a weaker one.
DILUTION
Solutions can be diluted simply by adding
more solvent and leaving the amount of solute
unchanged
What happens to molarity when a solution is
diluted?
More water has been added, so the total
volume of solution is greater but the amount
of solute is the same
Molarity will decrease!
Dilution
We use the following equation to perform dilution
calculations:
M1V1=M2V2
M1=Initial molarity
V1= Initial volume
M2= Final molarity
V2=Final volume
DILUTION EXAMPLE
1) What would be the resulting molarity of
2.500 L solution when the starting
solution had a molarity of 6.00 M and a
volume of 417 mL?
M1= 6.00 mol/L
V1= 417 mL
M1V1=M2V2
M2= ??
V2= 2500 mL
(6.00 mol/L)(417 mL) = (M2)(2500 mL)
(M2) = (6.00 mol/L)(417 mL)
(2500 mL)
M2 = 1.00 mol/L
Dilution
2) If I have 340 mL of a 0.5 M NaBr solution,
what will the concentration be if I add 560
mL more water to it?
0.19 M (the final volume is 900 mL, set up the equation
from that)
STOP
Work on some problems on your own
CONCENTRATION AND SOLUBILITY
The amount of solute affects both
solubility and dissolving rate.
A solvent can only dissolve so much
solute.
As the concentration increases, the ability
to dissolve more decreases, as does the
rate at which it will dissolve.
Solution Concentration
Unsaturated
When the amount of solute is less than the
maximum that could be dissolved
Saturated
When a solution holds the maximum amount of
solute
Fats!
You’ve all heard that we should avoid
saturated fats…so what does that mean?
Saturated fats (butter, dairy products, meat) are
solid at room temperature and are evenly filled
out with hydrogen. They increase the levels of
bad cholesterol (LDL) and clog your arteries.
Mono and poly unsaturated fatty acids (corn oil,
sunflower oil, and soybean oil, while omega 3 is
present in salmon, trout and tuna) remain liquid
at room temp and increase the levels of good
cholesterol!
Solution Concentration
Supersaturated
When a solution holds more than the maximum
amount and is thus unstable!
Supersaturated demo
http://www.youtube.com/watch?v=1y3bKI
Okcmk
SOLUBILITY CURVES
Show the amount of solute that can dissolve
in a solvent under normal circumstances at
a given temperature
The line for a given element on a set of
solubility curves is called the saturation line
Factors affecting Solvation
(aka rate of Dissolving)
Solvation: The act of surrounding solute
particles with solvent particles to form a
solution!
The solute is being pulled apart and
surrounded by the solvent.
Soluble – if you can dissolve any of the solute
Insoluble – if you can’t dissolve any
We can change this by changing many
different factors!
Factors Affecting Solvation
The rate at which the solute dissolves in the
solvent (link to KMT)
As Kinetic Energy increases, dissolving rate
increases
As Kinetic Energy decreases, dissolving rate
decreases
As the number of collisions increases, dissolving
rate increases
As the number of collisions decreases, dissolving rate
decreases
(1) TEMPERATURE AND DISSOLVING
RATE
Increasing the temperature speeds up the
movement of its particles
Allows for more collisions between solute
particles and solvent particles
(2) SURFACE AREA AND DISSOLVING
RATE
Breaking a solid into smaller pieces greatly
increases its surface area
More solvent particles can come into contact
with more particles of the solute
corresponding to increased surface area
Rate of collisions increases as surface area
increases
(3) AGITATION AND DISSOLVING
RATE
Agitation
Stirring, Mixing, Shaking
As agitation speed increases, rate of dissolving
increases
As the solvent moves around, more collisions
occur between solvent and solute particles
SUMMARY OF FACTORS AFFECTING
DISSOLVING RATES
As temperature ↑, dissolving rate ↑
As particle size ↓, surface area↑,
dissolving rate ↑
As agitation ↑, dissolving rate ↑
LAB
Factor’s affecting solubility lab
SOLUTIONS & SATURATION
Unsaturated
Saturated
Supersaturated
Definition
More solute can
dissolve in the
solvent
No more solute will
dissolve in the
solvent. If there is
extra undissolved
solute, it will settle
to the bottom of the
container.
Under unusual
circumstances
more solute is
dissolved in
solvent than it can
normally hold
Solubility
Curve
Below the
saturation line
On the saturation
line
Above the
saturation line
No
No, it is already
past saturation
point
Can you
Yes
Dissolve
More Solute?
SOLUBILITY CURVE
Let’s practice
reading a
solubility curve!
FACTORS AFFECTING SOLUBILITY
1. Temperature
2. Pressure
3. Polarity
FACTORS AFFECTING SOLUBILITY
(1) Temperature
Solids and Liquids: Generally, as temperature
increases, the solubility of solids and liquids
increases – why?
As temperature ↑, solubility ↑
Gases: Generally, as temperature increases, the
solubility of gases decreases – why?
As temperature ↑, solubility ↓
FACTORS AFFECTING SOLUBILITY
(2) Pressure
Solids and Liquids: no effect – why?
As pressure ↑, solubility is unaffected
Gases: Generally, as pressure increases, the
solubility of gases increases – why?
As pressure ↑, solubility of gases ↑
FACTORS AFFECTING SOLUBILITY
(3) Polarity!!
The nature of the solvent affects solubility
Like Dissolves Like
Ionic compounds, if they are soluble, dissolve in polar
solvents
Polar molecular (covalent) compounds dissolve in polar
solvents
Non-polar molecular (covalent) compounds dissolve in
non-polar solvents