Transcript Solutions

Solutions
Why does a raw egg swell or shrink when
placed in different solutions?
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Mixtures
•Two or more substances (elements and/or compounds)
combined but NOT chemically
–each substance keeps its properties
–Can be separated by physical properties
•Example: salt, sand, and water
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Heterogeneous mixture
•“Not well mixed”; different parts
–Parts can be easily separated
•Salad
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Homogeneous mixture
•“Well mixed”
–So well mixed that parts are difficult to
separate
•Cake batter
•Video Heterogeneous or homogeneous?
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- Understanding Solutions
Colloids and Suspensions
Types of Homogeneous mixtures
•Colloids and suspensions are mixtures that have
physical properties different from those of solutions.
•Colloid: small undissolved particles that never settle
(permanently suspended)
•Suspension: particles settle out or can be filtered to
separate
Some Definitions
A solution is a
_______________
mixture of 2 or more
substances in a
single phase.
One constituent is
usually regarded as
the SOLVENT and
the others as
SOLUTES.
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What Is a Solution?
•Solutions can be made from any combinations
of solids, liquids, and gases.
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Parts of a Solution
• SOLUTE – the
part of a solution
that is being
dissolved (usually
the lesser
amount)
• SOLVENT – the
part of a solution
that dissolves the
solute (usually
the greater
amount)
• Solute + Solvent =
Solution
Solute Solvent
solid
solid
solid
liquid
gas
solid
liquid
liquid
gas
liquid
gas
gas
Example
- Understanding Solutions
What Is a Solution?
•A solution has the same properties throughout at the molecular
level. It contains solute particles (molecules or ions) that are too
small to see.
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Particles in a Solution
•When a solution forms, particles of the solute
leave each other and become surrounded by
particles of the solvent.
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Effects of Solutes on Solvents
•At 0ºC, pure water freezes, but water mixed
with a solute does not. Solutes lower the
freezing point of a solvent.
Solid (frozen) water
Liquid water solution
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Pure water boiling
Salt Water Boiling
Pure water boils at
_______ degrees C?
Salt water boils at _______
degrees C.
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Identifying Main Ideas
Main Idea
A solution is a well mixed mixture that contains a solvent
and at least one solute.
Detail
Detail
The solvent
is the
substance
present in
the largest
amount.
A solute is a
substance
present in a
smaller
amount than
the solvent.
Detail
A solution
has the
same
properties
throughout.
Detail
A solution
contains
particles that
are too small
to see.
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Net Ionic
Predict a reaction between lead (II) nitrate by precipitation with
potassium iodide to determine if lead poisoning was the cause
of death for a child who ate a toy produced in China.
The forensics scientist doesn’t have any potassium iodide,
what could he use as an alternative that will cause a solid lead
(II) iodide to form.
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• It’s suspected that a beverage has been
tampered with by the addition of ice remover.
These are typically made of sodium chloride,
calcium chloride, magnesium chloride or a
combination of the three salts. Using the
solubility guidelines, create a strategy for
adding reagents that would cause
precipitation to determine which salt(s), if
any, were in the beverage. Indicate whether
any ion can’t be determined by precipitation.
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Net Ionic Q
• What is the net ionic equation for the
precipitation of magnesium phosphate from
the addition of magnesium nitrate to a sodium
phosphate solution? Name 2 alternatives you
could use.
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Definitions
Solutions can be classified as
saturated or unsaturated.
A saturated solution contains
the maximum quantity of
solute that dissolves at that
temperature.
An unsaturated solution
contains less than the
maximum amount of solute
that can dissolve at a
particular temperature
Example: Saturated and Unsaturated Fats
Saturated fats are
called saturated
because all of the
bonds between the
carbon atoms in a fat
are single bonds.
Thus, all the bonds
on the carbon are
occupied or
“saturated” with
hydrogen. These are
stable and hard to
decompose. The
body can only use
these for energy, and
so the excess is
stored. Thus, these
should be avoided in
diets. These are
usually obtained from
sheep and cattle fats.
Butter and coconut
oil are mostly
saturated fats.
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Unsaturated fats have at least one double bond
between carbon atoms; monounsaturated means
there is one double bond, polysaturated means
there are more than one double bond. Thus, there
are some bonds that can be broken, chemically
changed, and used for a variety of purposes.
These are REQUIRED to carry out many functions
in the body. Fish oils (fats) are usually
unsaturated. Game animals (chicken, deer) are
usually less saturated, but not as much as fish.
Olive and canola oil are monounsaturated.
Definitions
SUPERSATURATED SOLUTIONS
contain more solute than is
possible to be dissolved
Supersaturated solutions are
unstable. The supersaturation is
only temporary, and usually
accomplished in one of two ways:
1. Warm the solvent so that it will
dissolve more, then cool the
solution
2. Evaporate some of the solvent
carefully so that the solute does
not solidify and come out of
solution.
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Kidney Stones
• Urine volume plays a pivotal role in the process of stone formation. In
particular, low volume, highly concentrated urine contributes to the
supersaturation of elements normally found in the urine, such as
calcium oxalate. Fortunately, urine has the unique quality of holding
more solute in suspension than does water and so can accept large
concentrations of solute without precipitation. The ability of urine to
keep such large concentrations in solution is, in part, due to the
presence of protective organic molecules like citrate, as well as the
presence of charged ions which alter the solubility (Menon &
Resnick, 2002). Despite the fact that calcium oxalate can be present
in urine in concentrations 7 to 11 times its solubility in water (Menon
& Resnick, 2002), the point exists at which calcium oxalate exceeds
the unique properties of urine; crystals will then form and possibly
aggregate to form stones.
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Supersaturated
Sodium Acetate
• One application
of a
supersaturated
solution is the
sodium acetate
“heat pack.”
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Practice Problems
Compounds
Solubility (g/100 mL)
Sodium Cyanide (25 C)
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Cadmium Cyanide (25 C)
1.7
Potassium Cyanide (25 C)
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A 500.0-mL solution
contains 225 g of
potassium cyanide. Is the
solution saturated,
unsaturated or
supersaturated?
How many grams of
sodium cyanide are
needed to make 25 mL of
the saturated solution?
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IONIC COMPOUNDS
Compounds in Aqueous Solution
Many reactions involve ionic
compounds, especially reactions in
water — aqueous solutions.
KMnO4 in water
K+(aq) + MnO4-(aq)
Aqueous Solutions
How do we know ions are
present in aqueous
solutions?
The solutions can
conduct electricity.
They are called
ELECTROLYTES
HCl, MgCl2, and NaCl are
strong electrolytes.
They dissociate
completely (or nearly so)
into ions.
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Aqueous
Solutions
Some compounds
dissolve in water but
do not conduct
electricity. They are
called nonelectrolytes.
Examples include:
sugar
ethanol
ethylene glycol
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It’s Time to Play Everyone’s
Favorite Game Show… Electrolyte
or Nonelectrolyte!
http://chem
demos.uore
gon.edu/de
mos/Condu
ctivity-ofElectrolytes
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Beaker
Contents
Unknown 1
Unknown 2
Unknown 3
Water
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Conductivity Observations
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Which solution is which?
A.
B.
C.
D.
1 is sugar and 2 is salt
2 is sugar and 1 is salt
Both are sugar
Both are salt
E. What is 3?!
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Electrolytes and
Nonelectrolytes
• Electrolytes
– conduct electricity
– substances that release ions when dissolved in water
» This process is also called dissociation
or ionization
• Nonelectrolytes
– substances that do NOT dissociate in water
– do NOT conduct electricity
Ionic compounds (if they dissolve in water) are
always electrolytes.
Most molecular compounds are nonelectrolytes.
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If the atom-scale view of a compound in water
looks like the picture on the right (II.), you
might categorize the compound as…
I.
II.
a. Ionic
b. Molecular
c. Neither
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Ionic Compound Example
NaCl(s)  Na+(aq) + Cl- (aq)
Key features of ionic solid:
- Repeated units in larger lattice
- Units are made of charged ions
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Electrolytes in the Body
 Carry messages to
and from the brain
as electrical signals
 Maintain cellular
function with the
correct
concentrations
electrolytes
Make your own
50-70 g sugar
One liter of warm water
Pinch of salt
200ml of sugar free fruit
squash
Mix, cool and drink
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IONS
• calcium – in bone
and teeth. Also
important for muscle
contraction, blood clot
ting, and nerve
function.
• sodium – found
outside the cell.
Mainly involved
in water balance as
well as nerve
signaling.
• potassium – major
cation inside the cell.
Important for proper
functioning of heart,
muscles, kidneys, and
nerves.
• magnesium – in bone
and cells. Involved in
muscle,
bone, nervous
system, and takes
part in many
biochemical reactions.
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Gatorade
• Given the partial list of
ingredients of a sports
drink, which are
electrolytes and which are
non-electrolytes?
• Water H2O
• Sucrose Syrup, C12H22O11
• Sodium Citrate,K3C6H5O7
• Sodium Citrate,
Na3C6H5O7
• Sucralose (Splenda),
C12H19Cl3O8
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Concentration of Solute
The amount of solute in a solution
is given by its concentration.
Molarity (M) =
moles solute
liters of solution
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1.0 L of
water was
used to
make 1.0 L
of solution.
Notice the
water left
over.
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PROBLEM: A sodium nitrate solution is used to develop
fingerprints on porous objects, such as wood, by precipitating
any chloride ions in the fingerprint. The solution is prepared
by dissolving 30.0 g of silver nitrate in water to a final
volume of 1.00 L. What is it’s Molarity?
Step 1: Calculate moles
of silver nitrate
1 mol
30.00g •
= 0.177mol
170.89g
Step 2: Calculate Molarity
0.177 mol
= 0.177 M
1.00 L
[AgNO3] = 0.177 M
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PROBLEM: Fingerprints that have been deposited in blood
can be developed using an aqueous mixture with the dye
amido black. One of the main ingredients is a citric acid
solution prepared by dissolving 38.0 g of citric acid (C6H8O7)
to a final volume of 2.00 L. What is the Molarity?
• 0.0989 M C6H8O7
USING MOLARITY
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When the fingerprints in blood are on a painted surface that may
be damaged by the traditional methanol-based solution, an
alternative must be used with a 0.100 M citric acid solution.
Calculate the mass of citric acid to prepare 1.00 L of solution.
M=mol/V -> mol=M•V
Calculate.
0.100 mol C6H8O7
192.1 g
1.0 L 
•
= 192.1 g C6H8O7
1.00 L
1 mol C6H8O7
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Learning Check
How many grams of NaOH are required
to prepare 400. mL of 3.0 M NaOH
solution?
1) 12 g
2) 48 g
3) 300 g
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Dilution of Solute
Changing the concentration
a solution by adding solvent.
M1V1 = M2V2
initial
final
of
PROBLEM: A presumptitive test for LSD is the Ehrlich test
that requires a 3.25 M HCL solution. Concentrated
hydrochloric acid – the form in which most laboratories
purchase HCl – is 12.1 M. If a 100.0 mL sample of 3.25 M
HCl is needed, how many mL of the concentrated HCl should
be diluted?
Step 1: Plug
M1V1  M2V2
M1  12.1M
V1  ?
M2  3.25M
V2  100.0m L
Step 2: And Chug
(12.1M)V1  (3.25M)(100mL)
V1  26.9mLHCl
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PROBLEM: A presumptive test is a quick, cheap test that
indicates the drug of interest is most likely present. A
confirmatory test is required to definitely prove the drug is
present. For heroin, the presumptive test involves adding
mercury (II) chloride solution, which forms a rosette of
needle-shaped crystals if the heroin is present. The
directions for preparing the solution call for 13.9 mL of a
1.00 M stock solution diluted to 75 mL. What is the final
molarity of the mercury (II) chloride test solution?
Step 1: Plug
Step 2: And Chug
M1V1  M2V2
M1  1.00M
V1  13.9m L
M2  ?
V2  75.0m L
(1.00 M) (13.9mL)  (XM)(75.0m
L)
M2  0.185MHgCl2
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Concentration Units
An IDEAL SOLUTION is
one where the properties
depend only on the
concentration of solute.
Need conc. units to tell us the
number of solute particles
per solvent particle.
The unit “molarity” does not
do this! Volume changes
with temperature and mass
never changes!
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Two Other Concentration Units
MOLALITY, m
mol solute
m of solution =
kilograms solvent
% by mass
% by mass =
grams solute
grams solution
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Calculating Concentrations
Dissolve 62.1 g (1.00 mol) of ethylene glycol
in 250. g of H2O. Calculate molality and % by
mass of ethylene glycol.
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Calculating Concentrations
Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g
of H2O. Calculate m & % of ethylene glycol (by mass).
Calculate molality
1.00 mol glycol
conc (molality) =
 4.00 molal
0.250 kg H2O
Calculate weight %
62.1 g
%glycol =
x 100% = 19.9%
62.1 g + 250. g
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Learning Check
A solution contains 15 g Na2CO3 and 235 g of
H2O? What is the mass % of the solution?
1) 15% Na2CO3
2) 6.4% Na2CO3
3) 6.0% Na2CO3
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Using mass %
How many grams of NaCl are needed to
prepare 250 g of a 10.0% (by mass) NaCl
solution?
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Try this molality problem
• 25.0 g of NaCl is dissolved in 5000. mL of
water. Find the molality (m) of the resulting
solution.
m = mol solute / kg solvent
25 g NaCl
1 mol NaCl
58.5 g NaCl
= 0.427 mol NaCl
Since the density of water is 1 g/mL,
5000 mL = 5000 g, which is 5 kg
0.427 mol NaCl
5 kg water
= 0.0854 m salt water
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Colligative Properties
On adding a solute to a solvent, the properties
of the solvent are modified.
• Vapor pressure
decreases
• Melting point
decreases
• Boiling point
increases
• Osmosis is possible (osmotic pressure)
These changes are called COLLIGATIVE
PROPERTIES.
They depend only on the NUMBER of solute
particles relative to solvent particles, not on
the KIND of solute particles.
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Change in Boiling Point
Common Applications
of Boiling Point
Elevation
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Why?
• The density of water changes when something is added to
it and Demerol has a density of 1.037 g/mL. Analysis of a
sample requires investigating physical properties.
• Rubbing alcohol boils at 83C and water at 100C because of
IMFs.
• Vapor pressure is pressure exerted by molecules onto a
liquid. Boiling happens when vapor pressure is equal to the
pressure of the atmosphere.
• When you add a solute the vapor pressure is lowered, so
have to give even more E to make it equal to the external
pressure.
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Polluted Water Sample
• It is suspected that a local mine has been
polluting the river. A sample is sent to a lab to
investigate it. If the BP of the sample matches
that of regular water, does this mean that the
sample has no pollution?
It’s likely, but the toxic substance could be extremely low
levels that the BP is significantly changed or it could have
evaporated from solution or decomposed. Need further
testing!
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Change in Freezing Point
Pure water
Ethylene glycol/water
solution
The freezing point of a solution is LOWER
than that of the pure solvent
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DYNAMITE!
• Pure nitroglycerin is very
sensitive to shock and can be
detonated by dropping it or
freezing.
• Added ethylene glycol
dinitrate which has a much
lower freezing point.
• Alfred Nobel created the
Nobel Peace Prize because
he felt badly about creating
dynamite.
• Equilibrium - Blocks part of
the liquid solvent from
interacting with molecules in
the solid phase, but they can
reenter the liquid phase. The
solid molecules lose the
sufficient energy to reenter
that phase after a while so
start to refreeze.
Change in Freezing Point
Common Applications
of Freezing Point
Depression
Propylene glycol
Ethylene
glycol –
deadly to
small
animals
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Change in Freezing Point
Common Applications
of Freezing Point
Depression
Which would you use for the streets of
Bloomington to lower the freezing point
of ice and why? Would the temperature
make any difference in your decision?
a)
sand, SiO2
b)
Rock salt, NaCl
c)
Ice Melt, CaCl2
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Boiling Point Elevation and
Freezing Point Depression
∆T = K•m•i
i = van’t Hoff factor = number of particles
produced per molecule/formula unit. For
covalent compounds, i = 1. For ionic
compounds, i = the number of ions
present (both + and -)
Compound
Theoretical Value of i
glycol
1
NaCl
2
CaCl2
3
Ca3(PO4)2
5
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Boiling Point Elevation and
Freezing Point Depression
∆T = K•m•i
m = molality
K = molal freezing
point/boiling point constant
Substance
Kf
benzene
5.12
camphor
40.
carbon tetrachloride 30.
Substance
Kb
benzene
2.53
camphor
5.95
carbon tetrachloride 5.03
ethyl ether
water
ethyl ether
water
1.79
1.86
2.02
0.52
Change in Boiling Point
Dissolve 62.1 g of glycol (1.00 mol) in 250. g
of water. What is the boiling point of the
solution?
Kb = 0.52 oC/molal for water (see Kb table).
Solution
∆TBP = Kb • m • i
1.
2.
Calculate solution molality = 4.00 m
∆TBP = Kb • m • i
∆TBP = 0.52 oC/molal (4.00 molal) (1)
∆TBP = 2.08 oC
BP = 100 + 2.08 = 102.08 oC
(water normally boils at 100)
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Freezing Point Depression
Calculate the Freezing Point of a 4.00 molal
glycol/water solution.
Kf = 1.86 oC/molal (See Kf table)
Solution
∆TFP = Kf • m • i
= (1.86 oC/molal)(4.00 m)(1)
∆TFP = 7.44
FP = 0 – 7.44 = -7.44 oC
(because water normally freezes at 0)
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Freezing Point Depression
At what temperature will a 5.4 molal solution
of NaCl freeze?
Solution
∆TFP = Kf • m • i
∆TFP = (1.86 oC/molal) • 5.4 m • 2
∆TFP = 20.1 oC
FP = 0 – 20.1 = -20.1 oC
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Preparing Solutions
• Weigh out a solid
solute and dissolve in a
given quantity of
solvent.
• Dilute a concentrated
solution to give one
that is less
concentrated.
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ACID-BASE REACTIONS
Titrations
H2C2O4(aq) + 2 NaOH(aq) --->
acid
base
Na2C2O4(aq) + 2 H2O(liq)
Carry out this reaction using a TITRATION.
Oxalic acid,
H2C2O4
Setup for titrating an acid with a base
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Titration
1. Add solution from the buret.
2. Reagent (base) reacts with
compound (acid) in solution
in the flask.
3. Indicator shows when exact
stoichiometric reaction has
occurred. (Acid = Base)
This is called
NEUTRALIZATION.