Announcements & Agenda (02/14/07)
Happy Valentine’s Day!
Please pick up your exams up front.
GOOD NEWS
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Exam average was a ~76% - Nice job
Decided we will allow you to replace a low test score
with your final exam grade if it is higher
Starting next Wed - will hold an unofficial weekly review
@ 3pm, Room TBA
Agenda for the next 5 classes: Ch 7, Ch 8, & Movie
Today
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Exam Discussion
Solutions & Solution Properties (7.1-7.3)
Solution Concentrations (7.4)
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General Observations
Nice class average (~76%) – nice job!
Show as much work as possible
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tried to give as much partial credit as I could…
Some struggles with quiz-like questions
Be sure you understand objectives
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Exam 1 Results
What to do if….?
Go over the test – figure out what &
why?
 Make a plan…
 Come visit me to evaluate your
situation…
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Test 1 was:
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About what I expected
A bit challenging, but doable if I studied
Quite challenging – need to study more
Oh my!!! Time to talk to Bob…
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For those who did well… What did
you do to be successful?
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Solving problems, reviewing quizzes
Reviewing lectures
Reading the book
Working with somebody else
Just lots of time on all of the above
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CHAPTER 7: SOLUTIONS!
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Nature of Solutions
Solution – homogeneous mixture of two or
more substances
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Solvent – the main medium, present in the
largest quantity
Solute – material dissolved in the solvent
They don’t just have to be liquids:
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Nature of Solutes in Solutions
Solutes are
• spread evenly
throughout the
solution.
• cannot be separated
by filtration.
• can be separated by
evaporation.
• are not visible, but can
give a color to the
solution.
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Determination of Solubility
Definitions you may already know:
Solubility of solutes vary tremendously…
Miscible: when two liquids mix in all proportions
(Acetone and Water)
Immiscible: when two liquids DO NOT mix at all
(Oil and water)
Insoluble: when a solid does not dissolve in a
solvent (NaCl in gasoline)
Saturated: a solution that has dissolved the
maximum possible solute
REALITY IS USUALLY SOMEWHERE IN BETWEEN!
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Water: Nature’s Solvent
• is a polar molecule
• forms hydrogen bonds between the
hydrogen atom in one molecule and the
oxygen atom in a different water molecule.
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Hydrogen Bonding Reminder
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Formation of an Ionic Solution
Na+ and Cl- ions
• on the surface of a
NaCl crystal are
attracted to polar
water molecules.
• are hydrated in
solution with many
H2O molecules
surrounding each
ion.
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Solubility of Salts
• Must overcome strong +/- love between ions of the salt
(called lattice energy)
• Solution (pun intended) to the problem: ion-dipole
interactions – strength in numbers
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Equations for Solution Formation
When NaCl(s) dissolves in water, the
reaction can be written as
H2O
NaCl(s)
solid
Na+(aq) + Cl- (aq)
separation of ions
This is reality in ionic solutions!!!
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“Like Dissolves Like”
What does this mean?
Answer: compatibility of intermolecular
forces (last week)
Typically, compounds with similar polarity
will be soluble in each other.
Predicting trends based on properties…
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Like Dissolves Like
Solvents
Water (polar)
Ni(NO3)2
(polar)
CH2Cl2(nonpolar)
I2 (nonpolar)
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Example
Which of the following solutes will dissolve in
water? Why?
Yes, ionic
1) Na2SO4
2) gasoline
No, nonpolar
3) SiCl4
No, nonpolar
4) HCl
Yes, polar
Most polar and ionic solutes dissolve in
water
because water is a polar solvent.
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Which of the following vitamins are fat-soluble
and which are water soluble?
Vitamins: organic
molecules required for
proper function but not
made by the body.
(Obtain by eating!)
2 categories:
fat-soluble (dissolve in
fatty hydrocarbon-like
tissues)
water-soluble
Why we need at least some oil & fat in our diet!
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Electrolytes & Nonelectrolytes (7.2)
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Solutes and Ionic Charge
In water,
• strong electrolytes produce ions and conduct an
electric current.
• weak electrolytes produce a few ions.
• nonelectrolytes do not produce ions.
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Strong Electrolytes
• dissociate in water producing + & – ions
• conduct an electric current
• in equations show the formation of ions in
aqueous (aq) solutions.
H2O
NaCl(s)
100% ions
Na+(aq) + Cl− (aq)
H2O
CaBr2(s)
Ca2+(aq) + 2Br− (aq)
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Weak Electrolytes
• dissociate only slightly in water
• in water forms a solution of a few ions and mostly
undissociated molecules.
HF(g) +
H2O(l)
NH3(g) + H2O(l)
H3O+(aq) + F- (aq)
NH4+(aq) + OH- (aq)
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Nonelectrolytes
• dissolve as
molecules
• do not produce ions
• do not conduct an
electric current
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Electrolytes in the Body
Carry messages send to and from the
brain as electrical signals
Maintain cellular function with the correct
concentrations electrolytes
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Electrolyte balance in cells is important
Na+, Ca2+, Cl-
K+, Mg+2, X-
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Equivalents
An equivalent (Eq) is the amount of an electrolyte
or an ion that provides 1 mole of electrical charge
(+ or -).
1 mole Na+
=
1 equivalent
1 mole Cl−
=
1 equivalent
1 mole Ca2+
=
2 equivalents
1 mole Fe3+
=
3 equivalents
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Electrolytes in Body Fluids
In replacement solutions for body fluids, the
electrolytes are given in milliequivalents per liter
(mEq/L).
Ringer’s Solution
Na+ 147 mEq/L
K+
4 mEq/L
Ca2+
4 mEq/L
Cl−
155 mEq/L
The milliequivalents per liter of cations must equal
the milliequivalents per liter of anions.
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Solubility & Concentration (7.3-7.4)
• the maximum amount of solute that
dissolves in a specific amount of solvent.
• expressed as grams of solute in 100
grams of solvent water.
g of solute
100 g water
Unsaturated vs. Saturated Solutions
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Learning Check
At 40C, the solubility of KBr is 80 g/100 g H2O.
Identify the following solutions as either
1) saturated or 2) unsaturated. Explain.
A. 60 g KBr added to 100 g of water at 40C.
B. 200 g KBr added to 200 g of water at 40C.
C. 25 g KBr added to 50 g of water at 40C.
What happens to the “leftover” solute???
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Effect of Temperature on Solubility
• Depends on Temp!
• Solids: usually
increases as
temperature inc.
• Gases: usually
decreases as
temperature inc.
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Solubility and Pressure
Henry’s Law:
• Gas solubility is
directly related to
gas pressure above
the liquid
• at higher pressures,
more gas
molecules dissolve
in the liquid.
Real life examples… soda, the bends, etc.
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Percent Concentration (7.4)
The amount of solute dissolved in a specific
amount of solution.
amount of solute
amount of solution
Comes in all sorts of fantastic flavors!
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Mass Percent
•
Volume Percent
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Mass/Volume Percent
•
Molarity
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Mass Percent (% m/m)
• concentration is the percent by mass of
solute in a solution.
mass percent =
g of solute
x 100
g of solute + g of solvent
• amount in g of solute in 100 g of solution.
mass percent =
g of solute
x 100
100 g of solution
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Mass of Solution
8.00 g KCl
Add water to
give 50.00 g
solution
50.00 g KCl
solution
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Calculating Mass Percent
Calculation of mass percent (% m/m) requires the
• grams of solute (g KCl) and
• grams of solution (g KCl solution).
g of KCl
=
8.00 g
g of solvent (water)
=
42.00 g
g of KCl solution
=
50.00 g
8.00 g KCl (solute)
x 100 = 16.0% (m/m)
50.00 g KCl solution
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Volume Percent (% v/v)
• percent volume (mL) of solute (liquid) to volume
(mL) of solution.
volume % (v/v) =
mL of solute x 100
mL of solution
• solute (mL) in 100 mL of solution.
volume % (v/v) = mL of solute
100 mL of solution
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Mass/Volume Percent (% m/v)
• percent mass (g) of solute to volume (mL) of
solution.
mass/volume % (m/v) = g of solute x 100
mL of solution
• solute (g) in 100 mL of solution.
mass/volume % (m/v) =
g of solute x 100
100 mL of solution
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Percent Conversion Factors
Two conversion factors can be written for
each type of % value.
TABLE 7.7
5% (m/v) glucose
There are 5 g of glucose
in 100 mL of solution.
5 g glucose
100 mL solution
and
100 mL solution
5 g glucose
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How many grams of NaOH are needed to
prepare 75.0 g of 14.0% (m/m) NaOH solution?
1) 10.5 g NaOH
2) 75.0 g NaOH
3) 536 g NaOH
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Solution
1)10.5 g NaOH
75.0 g solution x 14.0 g NaOH = 10.5 g NaOH
100 g solution
14.0% (m/m) factor
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How many milliliters of a 5.75% (v/v) ethanol
solution can be prepared from 2.25 mL ethanol?
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1) 2.56 mL
2) 12.9 mL
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3) 39.1 mL
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Solution
3) 39.1 mL
2.25 mL ethanol x 100 mL solution
5.75 mL ethanol
5.75% (v/v) inverted
= 39.1 mL solution
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