Transcript Properties of Solutions - Vernon Hills High School

FACTORS AFFECTING
SOLVATION
14.3: Pgs. 489 - 497
STEP 1 OF LAB
1.
2.
3.
4.
5.
6.
Obtain a CLEAN test tube!!!
Place 2.2 grams of Na2SO4 into a test tube
and add 10mL of water.
Dissolve the solid: Heat the test tube in a
bunsen burner until you hear a “pop”.
Remove the test tube from the bunsen burner
and stir the contents with a stirring rod.
Continue this process until the solid
dissolves.
Place the test tube into the test tube rack
when the solid is dissolved.
Place 2 ice cubes into a beaker and fill the
beaker with water (You will use this later)
Sit back in your seat.
SOLUTION FORMATION

What did you do to make the solid dissolve faster?
SOLUTION FORMATION

Factors Affecting Solubility Rate:
1.
Agitation  stirring increases the rate at which a
solute dissolves

2.
3.
Temperature  hot solvents dissolved solutes
faster than cold solvents
Particle Size  fine powders dissolve more
rapidly than large particles

4.
Only affects the rate, NOT the amount!
Think about sugar cubes vs. table sugar!
Pressure  refers to gases only!
SOLUBILITY

Saturated Solutions: contain the maximum
amount of solute for a given amount of solvent


Solubility is the amount of solute that dissolves in a
given quantity of a solvent at a given temperature to
produce a saturated solution (i.e. NaCl = 36.2g per
100 mL H2O)
Unsaturated solutions contain less than the
maximum
SOLUBILITY
STEP 2 OF THE LAB
1
person from your team must place your test
tube into the beaker of ice water and then
return to your seat.
DYNAMIC EQUILIBRIUM

In saturated solutions,
the rate of new
particles dissolving vs.
dissolved particles
recrystalizing is
EQUAL!
SOLUBILITY

Supersaturated solutions

Contains more solute than is allowed at a given
temperature.
SOLUBILITY OF GASES


Gases have greater solubility in
cold water then hot water 
why?
Gas solubility increases as the
partial pressure above the
solution increases – why?
SOLUBILITY OF
GASES
Sodas are bottled at
HIGH pressures!
 When the bottle is
opened, the CO2 escapes
because the partial
pressure of CO2 above the
liquid decreases

SOLUBILITY OF GASES

Henry’s Law

At a given temperature, the solubility of a gas (S) is
directly proportional to the pressure (P) of the gas above
the liquid
s1 s 2

P1 P2
PRACTICE PROBLEM:
 If
the solubility of a gas in water is 0.77g per
100mL of water at 3.5atm of pressure, what is
its solubility (in g per 100mL of water) at
1.0atm of pressure. (Assume the temperature
remains constant.)
LAST STEP OF THE LAB
GENTLY remove the test tube from the cold
water. Add a small amount of Na2SO4 and
observe.
 Clean up the lab: All solution/compounds can be
rinsed down the drain.
 Sit back in your seat.

WHAT HAPPENED?
 How
should we label the solution before we
added the crystal?
Supersaturated solution
 Contains more solute than is allowed at a given
temperature.



Supersaturated solutions are unstable.
 If a small crystal of the solute is added to a supersaturated
solution, the excess immediately crystallizes out.
How should we label the solution after the crystal was
added?

unsaturated
YESTERDAY WE COVERED…

4 factors that will increase the rate of dissolution
Today we will cover…

How temperature not only increases
the rate of dissolution, temperature
also affects the amount that can
dissolve.
FACTORS AFFECTING SOLUBILITY

Solubility is VERY temperature dependent!


Ex: 36.2g of NaCl dissolves in 100g H2O at 25oC,
HOWEVER 39.2g NaCl can dissolve in 100g H2O at
100oC!
For most substances, solubility increases as
temperature of the solvent increases
SOLUBILITY
CURVES

What substance has
the highest solubility
at 50oC? (exclude
KI)

What has the lowest
at 50oC?
PROBLEM:

I dissolved 5.2g of a substance into 16g of water.
What is the solubility of this substance in units of
g / 100g of water?
SOLUBILITY CURVE LAB
Not all substances are stable enough to create a
supersaturated solution. Most substances can
only form a saturated solution.
 We will complete this as a class. Each pair of
students will be assigned a specific amount of
salt to use and we will collaborate our data to
create a lab report.
