Solutions
Big Idea
Chemical
and Physical Properties of
materials can be explained by the
structure and the arrangement of
atoms, ions or molecules and the
forces between them.
Essential Knowledge
Chemical
Analysis provides a
method for determining the relative
number of atoms in a substance,
which can be used to identify the
substance or determine its purity.
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1
Solution Vocabulary
The
solvent does the dissolving.
The solute is dissolved.
There are examples of all types of
solvents dissolving all types of
solvent.
We will focus on aqueous solutions.
Various Types of Solutions
State of
Solution
Example
State of Solute
State of
Solvent
Air, natural gas
Gas
Gas
Gas
Vodka, antifreeze
Liquid
Liquid
Liquid
Brass
Solid
Solid
Solid
Carbonated water (soda)
Liquid
Gas
Liquid
Seawater, sugar solution
Liquid
Solid
Liquid
Hydrogen in platinum
Solid
Gas
Solid
5
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Concentration of Solutions
Molarity
= moles of solute
Liters of solution
% mass = Mass of solute
x 100
Mass of solution
Mole fraction of component A
χA =
nA
nA + nB
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Concentration of Solutions
Molality
=
Molality
is abbreviated m
Normality
moles of solute
Kilograms of solvent
-skip
Exercise
What is the percent-by-mass concentration
of glucose in a solution made my
dissolving 5.5 g of glucose in 78.2 g of
water?
6.6%
8
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Exercise
A solution of phosphoric acid was made by
dissolving 8.00 g of H3PO4 in 100.0 mL of
water. Calculate the mole fraction of H3PO4.
(Assume water has a density of 1.00 g/mL.)
0.0145
9
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Page 3
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Exercise
A solution of phosphoric acid was made by
dissolving 8.00 g of H3PO4 in 100.0 mL of
water. Calculate the molality of the
solution. (Assume water has a density of
1.00 g/mL.)
0.816 m
10
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Inquiry Question
Consider
two aqueous solutions, A
and B (which contain different
solutes). Is it possible for solution A
to have a greater concentration than
solution B in terms of mass percent,
but a smaller concentration in terms
of molarity? If no, explain why not. If
yes, provide an example. What if the
solutions contained the same
solute?
Concentration Vocabulary
Dilute
vs Concentrated Activity
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Big Idea
Chemical
and Physical Properties of
materials can be explained by the
structure and the arrangement of
atoms, ions or molecules and the
forces between them.
Essential Knowledge
Net
changes in energy for a chemical
reaction or a physical change can be
endothermic or exothermic.
Energy of Making Solutions
Heat
of solution ( ∆Hsoln ) is the energy
change for making a solution.
Most easily understood if broken into
steps.
1.Break apart solvent
2.Break apart solute
3. Mixing solvent and solute
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Steps in the Dissolving Process
16
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1. Break apart Solvent
Have
to overcome attractive forces.
∆H1 >0
2. Break apart Solute.
Have
to overcome attractive forces.
∆H2 >0
3. Mixing solvent and solute
This
explains the rule “Like dissolves
Like”
∆H3 depends on what you are mixing.
If molecules can attract each other
∆H3 is large and negative.
Molecules can’t attract- ∆H3 is small
and negative.
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Enthalpy (Heat) of Solution
19
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Enthalpy (Heat) of Solution
20
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Enthalpy (Heat) of Solution
If
∆Hsoln is small and positive, a
solution will still form because of
entropy.
There are many more ways for them
to become mixed than there is for
them to stay separate.
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Big Idea
Chemical
and Physical Properties of
materials can be explained by the
structure and the arrangement of
atoms, ions or molecules and the
forces between them.
Essential Knowledge
The
solubility of a substance can be
understood in terms of chemical
equilibrium.
Solubility
Def
≡ The amount of substance
solute that dissolves in a given
volume of solvent at a given
temperature
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Solubility
Solubility
Ksp
Solubility
product constants are
used to describe saturated solutions
of ionic compounds of relatively low
solubility.
Solubility
A
saturated solution is in a state of
dynamic equilibrium between the
dissolved, dissociated, ionic
compound and the undissolved
solid.
MxAy(s) --> x My+(aq) + y Ax-(aq)
The general equilibrium constant for
such processes can be written as:
Ksp = [My+]x[Ax-]y
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Solubility
Ksp
If
an ionic compound is “insoluble”,
what kind of value would you
expect?
Soluble?
Ksp Calculation
Calculating
Ksp's from Solubility Data In
order to calculate the Ksp for an ionic
compound you need the equation for the
dissolving process so the equilibrium
expression can be written.
You also need the concentrations of each
ion expressed in terms of molarity, or
moles per liter, or the means to obtain
these values.
Calculating Ksp
Calculate
the solubility product
constant for lead(II) chloride, if 50.0
mL of a saturated solution of lead(II)
chloride was found to contain 0.2207
g of lead(II) chloride dissolved in it.
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Calculating Ksp
First,
write the equation for the
dissolving of lead(II) chloride and the
equilibrium expression for the
dissolving process.
PbCl2(s) --> Pb2+(aq) + 2 Cl-(aq)
Ksp = [Pb2+][Cl-]2
Calculating Ksp
Second,
convert the amount of
dissolved lead(II) chloride into moles
per liter.
(0.2207 g PbCl2)(1/50.0 mL solution)(1000 mL/1 L)(1 mol PbCl2/278.1 g PbCl2)
= 0.0159 M PbCl2
Calculating Ksp
Place
Values in the Solubility
Product Expression
PbCl2(s) --> Pb2+(aq) + 2 Cl-(aq)
[0.0159]
[0.0159]
[0.0318]
2+
2
Ksp = [Pb ][Cl ]
Ksp = [0.0159][0.0318]2 = 1.61 x 10-5
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Big Idea
Chemical
and Physical Properties of
materials can be explained by the
structure and the arrangement of
atoms, ions or molecules and the
forces between them.
Essential Knowledge
Intermolecular
forces play a key role
in determining the properties of
substances, including biological
structures and interactions.
Factors Affecting Solubility
Structure
of the molecule
• Polarity
Pressure
• Henry’s Law
Temperature
• Affect on aqueous solutions
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Factors Affecting Solubility: Structure
soluble molecules must have
dipole moments -polar bonds.
To be soluble in nonpolar solvents
the molecules must be non polar.
Read Vitamin A - Vitamin C, water
soluble vitamins
Water
Factors Affecting Solubility: Structure
Structure of Soap
CH2
CH3
CH2
CH2
P
CH2
CH2
CH2
O-
CH2
O-
O-
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Structure of Soap
CH2
CH3
CH2
CH2
CH2
CH2
O-
P
CH2
CH2
O-
O-
Hydrophobic
non-polar
end
Soap
CH2
CH3
CH2
OO-
O-
CH2
CH2
CH2
P
CH2
CH2
Hydrophilic
polar end
O-
CH2
CH3
CH2
CH2
P
CH2
CH2
CH2
CH2
O-
O-
_
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A
drop of grease in water
Grease is non-polar
Water is polar
Soap lets you dissolve the non-polar
in the polar.
Hydrophobic
ends dissolve in
grease
Hydrophilic ends
dissolve in water
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Water
molecules can surround and
dissolve grease.
Helps get grease out of your way.
Factors Affecting Solubility: Pressure
Changing
the pressure doesn’t affect
the amount of solid or liquid that
dissolves
• They are incompressible.
Changing the pressure does affect
gases.
• Why is it important to understand
this?
– Blood gases, Manufacture of Pop
Dissolving Gases
Pressure
affects the
amount of gas that
can dissolve in a
liquid.
The dissolved gas is
at equilibrium with the
gas above the liquid.
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The
gas is at
equilibrium with the
dissolved gas in this
solution.
The equilibrium is
dynamic.
If
you increase the
pressure the gas
molecules dissolve
faster.
The equilibrium is
disturbed.
Pressure Effects
51
Henry’s law:
Amount of gas dissolved in a solution is
directly proportional to the pressure of
the gas above/outside of the solution.
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Application of Henry’s Law
When people work in a space where the air
pressure is much above normal, they have to be
careful to return slowly to the
atmosphere. Otherwise, they face the danger of
the "bends." The bends are severe pains in the
joints and muscles, fainting, possible deafness,
paralysis, and death. Workers building deep
tunnels, where higher than normal air pressure is
maintained to keep water out, are at risk, so are
deep-sea divers and scuba divers who stay down
for to prolonged a period.
The bends develop because the solubilities of
both nitrogen and oxygen are higher under higher
pressure, as Henry's Law states. Once the blood
is enriched in these gases it must not be allowed
to lose them suddenly. If the person returns to
normal atmospheric pressure to rapidly the blood
will act like a soda pop bottle and fizz. If
microbubbles of nitrogen and oxygen appear at
blood capillaries, they will block the flow of
blood. Such a loss is particularly painful at
joints, and any reduction in blood flow to the
brain can be extremely serious.
Application of Henry’s Law
Henry’s Law: Pressure Effects
Henry’s law:
C = kHP
C
=
concentration of dissolved gas, M
kH
P
=
=
Henry’s Law constant, M/atm
partial pressure of gas solute
above the solution, atm
Conditions when this holds true:
•
•
54
Dilute solutions
Gas does not interact with solvent
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Page 18
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Henry’s Law Example
How many grams of carbon dioxide gas is
dissolved in a 1.00 L bottle of carbonated water if
the manufacturer uses a pressure of 2.40 atm in
the bottling process at 25 °C?
Given: KH of CO2 in water = 29.76 atm/(mol/L) at 25 °C
Henry’s Law Example
P = KHC
P is the partial pressure of the gas above the
solution
KH is the Henry's Law constant for the solution
C is the concentration of the dissolved gas in
solution
C = P/KH
C = 2.40 atm/29.76 atm/(mol/L)
C = 0.0806 mol/L
since we only have 1 L of water, we have 0.08 mol of CO2.
Henry’s Law Example
Convert
moles to grams
g of CO2 = 0.0806 mol x 44 g/mol
g of CO2 = 3.52 g
There are 3.52 g of CO2 dissolved in a 1 L bottle of
carbonated water from the manufacturer.
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Factors Affecting Solubility: Temperature
Increased
temperature increases the
rate at which a solid dissolves.
We can’t predict whether it will
increase the amount of solid that
dissolves.
We must read it from a graph of
experimental data.
The
Solubilities
of Several
Solids as a
Function of
Temperature
59
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Gases are predictable
As
temperature
increases, solubility
decreases.
Gas molecules can
move fast enough to
escape.
Thermal pollution.
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Temperature Effect on Gas Solubility
The
Solubilities
of Several
Gases in
Water
62
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Big Idea
Chemical
and Physical Properties of
materials can be explained by the
structure and the arrangement of
atoms, ions or molecules and the
forces between them.
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Essential Knowledge
Intermolecular
forces play a key role
in determining the properties of
substances, including biological
structures and interactions.
Vapor Pressure of Pure Solvent vs Solution
Vapor Pressure of Solutions
A
nonvolatile solvent lowers the
vapor pressure of the solution.
The molecules of the solvent
must overcome the force of
both the other solvent
molecules and the
solute molecules.
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Water
has a higher vapor
pressure than a solution
Aqueous
Solution
Pure water
Water
evaporates faster from for
water than solution
Aqueous
Solution
Pure water
The
water condenses faster in the
solution so it should all end up
there.
Aqueous
Solution
Pure water
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Skills Needed for Today’s Notes
mole fraction of particles of solvent
Raoult’s Law:
Psoln
= χsolvent x Psolvent
Vapor pressure of the solution
• mole fraction of solvent
• vapor pressure of the pure solvent
Applies only to an ideal solution
where the solute doesn’t contribute
to the vapor pressure
• “Nonvolatile solute”
•
Vapor Pressures of Solutions
Nonvolatile solute lowers the vapor
pressure of a solvent.
Raoult’s Law: Psolution = Psolvent χsolvent
Psolution = observed vapor pressure of solution
χ solvent = mole fraction of particles of solvent
Psolvent= vapor pressure of pure solvent
On the AP HELP SHEET:
72
PA = Ptotal
χ
A
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Vapor Pressures of Solutions
Raoult’s Law: PA = Ptotal χA
• Complete the following statement:
• The vapor pressure of the solvent will
change when…
• The adjusted vapor pressure depends on #
solute components.
• How would the TYPE of solute affect the
mole fraction?
• How would a molecular solute behave
when dissolved in water? An ionic solute?
73
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4 Types of Raoult’s Law Problems
Solution
of nonvolatile
nonelectrolytic solute in a solvent
Solution of a nonvolatile electrolytic
solute in a solvent
Solution of 2 volatile substances
Finding Molar Mass using Raoult’s
law
Raoult’s Law General Problem
A
solution of cyclopentane with a
nonvolatile compound has vapor
pressure of 211 torr. If vapor
pressure of the pure liquid is 313
torr, what is the mole fraction of the
cyclopentane?
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Raoult’s Law Nonvolatile
nonelectrolytic solute
A
solution of cyclopentane with a
nonvolatile compound has vapor
pressure of 211 torr. If vapor
pressure of the pure liquid is 313
torr, what is the mole fraction of the
cyclopentane?
• The adjusted vapor pressure depends on
# solute components.
• How is this formula affected by an electrolytic
compound?
• For example:
• 2 moles of Copper II chloride is dissolved in
10 moles of water
Raoult’s Law Nonvolatile
electrolytic solute
Calculate
the vapor pressure of the
solution when 55 grams of KI are
added to 325 mL of water at 25°C.
The vapor pressure of water at 25°C
is 23.8 mm Hg.
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Raoult’s Law Finding Molar
Mass of the Solute
Solute and Solvent are volatile
Liquid-liquid
solutions where both are
volatile.
Both contribute to the vapor pressure
Modify Raoult’s Law to
PA + PB = χAPAtotal + χBPBtotal
Ptotal = expected vapor pressure of
mixture
PAtotal= vapor pressure of pure A
Ptotal =
Solute and Solvent are volatile
Reminder
Σ
about χ
χ = _______
A
solution is made up of 2 volatile
substances, a & b.
If χa = .452, what is χb ?
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Practice Question
is the composition of a
pentane-hexane solution that has a
vapor pressure of 350 torr at 25ºC ?
The vapor pressures at 25ºC are
• pentane 511 torr
• hexane 150 torr.
What is the composition of the
vapor?
Vapor Pressure
What
P of pure A
P of pure B
χA
χb
Deviations (Nonideal Solutions)
If
solvent has a strong affinity for
solute (ex.H bonding) or concentrated
solution
Lowers solvent’s ability to escape.
Lower vapor pressure than expected.
Negative deviation from Raoult’s law.
∆Hsoln is large and negative
exothermic.
Endothermic ∆Hsoln indicates positive
deviation.
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Vapor Pressure
Positive deviationsWeak attraction between
solute and solvent
Positive ∆Hsoln
Vapor Pressure
χA
χb
Negative deviationsStrong attraction between
solute and solvent
Negative ∆Hsoln
χA
χb
Big Idea
Chemical
and Physical Properties of
materials can be explained by the
structure and the arrangement of
atoms, ions or molecules and the
forces between them.
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Essential Knowledge
Intermolecular
forces play a key role
in determining the properties of
substances, including biological
structures and interactions.
Colligative Properties
Because
dissolved particles affect
vapor pressure - they affect phase
changes.
Colligative properties depend only
on the number - not the kind of
solute particles present
Useful for determining molar mass
Molal Freezing Point/Boiling Point Constants
pg 517
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Boiling point Elevation
Because
a non-volatile solute lowers
the vapor pressure it raises the boiling
point.
∆T = Kbmsolute
∆T
is the change in the boiling point
Kb is a constant determined by the
solvent.
msolute is the molality of the solute
Boiling Point Elevation
∆T = Kbmsolute
At
what temperature will a solution
that is composed of 0.73 moles of
glucose in 650.0 mL of water begin to
boil?
At what temperature will a sucrose
solution, C11H22O11, boil if it contains
175 grams of sucrose in 750. mL of
water?
Boiling Point Elevation
What
mass (in g) of a nonelectrolytic
molecular substance (MW = 50.0 g/mol)
must be added to 500. g of water to
produce a solution that boils at
101.56 ºC?
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Freezing Point Depression
Because
a non-volatile solute lowers
the vapor pressure of the solution it
lowers the freezing point
∆T = Kf msolute
∆T is the change in the freezing point
Kf is a constant determined by the
solvent
msolute is the molality of the solute
Freezing Point Depression
∆T
= Kf msolute
At
what temperature will an methanol
solution, CH3OH, freeze if it contains
55.0 grams of methanol in 1200. mL
of water?
At what temperature will a solution of
ethylene glycol (C2H6O2)freeze if it
contains 120. grams of ethylene
glycol in 500.0 mL of water?
Calculating Molar Mass
Vitamin
B2, riboflavin, is soluble in
water. If 0.833 g of riboflavin is
dissolved in 18.1 g H2O, the resulting
solution has a freezing point of
-0.227 ºC. What is the molar mass of
riboflavin?
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Background: Van’t Hoff factor, i
Van’t
Hoff corrects for the fact that the
number of particles you thrown into
solution is not always the number of
particles that determine the magnitude
of the property.
Van’t Hoff factor, i
For
example, think about what happens when
you put the following one mole quantities into
a liter of water. Which one raises the boiling
point the most?
Van’t Hoff factor, i
Electrolytes
have a bigger impact on on
melting and freezing points per mole
because they make more pieces.
Relationship is expressed using the van’t
Hoff factor i
i = Moles of particles in solution
Moles of solute dissolved
The expected value can be determined
from the formula of the compound.
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Example
Predict
the van't Hoff factor for
Sr(OH) 2
What
is the van't Hoff factor for
Fe(NO 3 ) 3
Example
Determine
the freezing point of a
1.77 m solution of NaCl in H 2 O
Example
Determine
the boiling point of a
solution made up of dissolving 49.19
g of CaCl 2 in 500. mL of H 2 O
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Big Idea
Chemical
and Physical Properties of
materials can be explained by the
structure and the arrangement of
atoms, ions or molecules and the
forces between them.
Essential Knowledge
Intermolecular
forces play a key role
in determining the properties of
substances, including biological
structures and interactions.
Osmotic Pressure
When
two solutions of different
concentrations are separated by the
right kind of membrane, their
concentrations change in the
direction of becoming equal.
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Example of Osmotic Pressure
In
living things, membranes of various
kinds keep mixtures organized and
separated.
These membranes are semipermeable,
which means that they let water molecules
as well as small ions and other small
molecules pass through.
However they do not allow the passage of
very large molecules, like those of
proteins.
Example (continued)
This
phenomenon, the selective
passage of small ions and molecules
through a membrane, is
called dialysis, and the membrane is
a dialyzing membrane.
Example (continued)
In
the limiting case of
dialysis, osmosis, only solvent
molecules can get through the
membrane, now called an osmotic
membrane. Such membranes are
rare, but they can be made.
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What is osmosis?
One
theory that can be used to
explain osmosis is that an osmotic
membrane separates two solutions
from each other, one solution being
more concentrated in solute than the
other. The solvent in each solution
has its own "escaping tendency",
which is just like the vapor pressure
of a solution.
What is osmosis?
The
solution with the lower solute
concentration has, of course, the
higher mole fraction
of solvent. Therefore, solvent
molecules in the less concentrated
solution (or the pure solvent) have a
higher escaping tendency than those
in the more concentrated solution.
What is osmosis?
So
solvent molecules escape
through the membrane more
frequently from the less
concentrated side and pass into the
more concentrated solution.
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Osmosis
The
effect is a net shift of solvent
through the membrane from the less
concentrated side to the more
concentrated side. This is osmosis,
and it will continue, in principle, until
the concentrations of the solutions
become equal.
http://molit.concord.org/database/activities/23.html
Application To Biology
Osmotic Pressure
= MRT
molarity of solute
R: ideal gas law constant
• 0.0821 L atm/mol K
T: temperature, K
π: Osmotic pressure, atm
π
M:
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Osmotic Pressure
= MRT
A very dilute solution, 0.0010 M
sugar in water, is separated from
pure water by an osmotic
membrane. What osmotic pressure
developed at 25oC ?
π
Inquiry Question: Your Choice
Why
would it be deadly to give a
hospital patient distilled water
instead of saline?
Why would it be a major problem for
a salt water fish to be placed in fresh
water?
Inquiry Lab
Design
an experiment that would
demonstrate different types of
solutes dissolved in the solvent
water and their effects on osmotic
pressure of an egg.
Hint:
First step in the lab will be to
get rid of the shell of the egg.
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