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Chemistry 354
Organic Chemistry Laboratory I
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Safety
The organic chemistry safety presentation on the web
is available on the web at the following address:
http://atom.chem.wwu.edu/dept/osafety/index.htm.
Read pp 542 – 558 in the lab book. We administer the
safety quiz online at the following URL:
http://argon.chem.wwu.edu/SafetyQ/OCQLink.htm A
link to the safety quiz is included at the bottom of the
instruction page.
You will have 30 minutes to complete the 25 question
quiz.
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Safety
First Try: Tuesday, June 20, 8AM to Friday, June 23,
10AM
Second Try: Tuesday, June 20, 8:00 AM to Friday,
June 23, 10 AM
Third Try: Tuesday, June 20, 8:00AM to Friday, June
12, 10 AM
In order to be enrolled in this course, each student
will be required to take and pass a laboratory safety
quiz. You must pass the quiz before Tuesday, April
6th at NOON. If you cannot successfully pass the
quiz, you will be dropped from this course.
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Chemistry 354 Lecture
• Purpose: To ensure that each student,
regardless of laboratory section and
instructor, receives the same information in
preparation for the experiment.
• Examinations: The midterm and final
examinations will be given in this lecture
session.
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Introduction to Microscale
Laboratory
• Read:
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–
–
–
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Experiment 1 (pp. 2 – 13)
Technique 1 (pp. 542 – 558)
Technique 2 (pp. 558 – 565)
Technique 3 (pp. 566 – 573)
Technique 4 (pp. 574 – 580)
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Introduction to Microscale
Laboratory
• Macroscale: Quantities of chemicals
on the order of 5 to 100 grams.
Glassware containers up to 500 mL.
• Microscale: Quantities of chemicals
on the order of 0.050 to 0.100 grams.
Glassware containers up to 25 mL.
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Introduction to Microscale
Laboratory
• Heating
– No flames
• Dispensing of liquids
• Assignment:
– Laboratory exercise 1 (parts A and B)
– Laboratory exercise 2
• There is no pre-lab or laboratory
report required for this assignmentWWU -- Chemistry
Experiment 2: Solubility
• Reading Assignment
– Experiment 2 (pp.13 – 20)
– Technique 5 (pp. 581 – 589)
– Technique 10 (pp. 637 – 646)
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• NOTE: You will be expected to submit
a pre-lab assignment before you begin
this experiment!
• Consult the syllabus for your
laboratory section for the due date for
the pre-lab exercise and for the final
laboratory report.
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Solubility
• The extent to which a substance is
soluble in a solvent.
• Examples (solubility in water at 25°C):
– Cholesterol
– Caffeine
– Citric acid
0.002 mg/mL
22 mg/mL
620 mg/mL
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Solubility -- Definitions
• Solute: The substance that is being
dissolved
• Solvent: The medium in which the
solute is being dissolved.
• NOTE: In a solution, the solvent
molecules greatly outnumber the
solute molecules.
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If a liquid organic compound is
dissolved in a solvent…
• Miscible: solute and solvent mix
homogeneously in all proportions
• Immiscible: solute and solvent do
not mix; they form two separate liquid
phases
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Part A: Solubility in a Series of
Solvents
O
Benzophenone
C
O
HO
C
O
CH2
C
OH
Malonic acid
Biphenyl
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Some hints on doing the solubility lab:
1. You can do the various parts of the experiment in
any order you wish! This eliminates lineups by the
Balances. Part A is especially time consuming!
2. Be sure to approximate the amounts of solids you
are using in Part A. You don’t need to be exact
on the weights.
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• You will study the solubility behavior of
benzophenone, malonic acid, and
biphenyl in:
• Water, methanol, hexane
• How does the polarity of the solute
influence the solubility in each of these
solvents? What factors are at play, here?
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Make a guess as to the solubility of malonic acid in
water. Notice that the acid has two very polar carboxyl
groups in the compound.
O
HO
C
O
CH2
C
OH
Malonic acid
Would you expect this compound to be soluble in
the non-polar hexane solvent?
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How consider the solubility of biphenyl in water.
Make a guess as to the whether it will be soluble in
water.
Biphenyl
What about the solubility in hexane?
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Solubility Rule
“Like Dissolves Like”
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Why Does The Rule Work?
• If a substance is to dissolve in a
solvent, the intermolecular attractions
between solute molecules and solvent
molecules must be similar in strength
as the solute-solute and solventsolvent intermolecular attractions.
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Types of Intermolecular
Attractions
• Dipole-dipole attractions
• Hydrogen-bonding
• Van der Waal (London) forces
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Part B. Solubility of Different
Alcohols
• Solutes:
CH3 OH
Methanol
• Solvents
– Water
– Hexane
CH3 CH2 CH2 CH2 OH
1-Butanol
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 OH
1-Octanol
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All three of these alcohols have a polar hydroxyl
group. However, the rest of the molecule has a
non-polar hydrocarbon chain.
OH
OH
1-octanol
1-butanol
H
C
OH
methanol
H
H
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• How does the length of the carbon chain
influence the solubility of the test alcohol
in water?
• How does the length of the carbon chain
influence the solubility of the test alcohol
in hexane?
• What accounts for any differences?
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Part C. Miscible or Immiscible
Pairs
• Here we examine pairs of compounds
to determine whether or not they are
miscible (soluble).
• How do differences in polarity affect
solubility?
• How do intermolecular attractions
influence the solubility of a solute in a
particular solvent?
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Part D. Solubility of Organic
Acids and Bases
• Solutes:
O
C
OH
Benzoic acid
O
H2N
C
O
Ethyl 4-aminobenzoate
CH2 CH3
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• What is the important component in 1.0
M NaOH? What is the important
component in 1.0 M HCl?
• What principle explains the solubility of a
substance in aqueous acid or aqueous
base?
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Many covalent organic molecules are not very soluble
in water even if they are somewhat polar! Benzoic
acid is an example.
O
OH
Acidic carboxyl
group
When benzoic acid is reacted with sodium hydroxide,
it is converted to an ionic substance (sodium salt),
The ionic substance is now much more soluble in
water! Ionic substances are very polar!
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• When benzoic acid reacts with
sodium hydroxide, what happens to
the covalent molecule?
O
O
H
O-H
Na
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Benzoic acid is converted to an ionic compound!
O
O
Na
+
O
H
H
Ionic compounds are soluble in water!
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Compounds with amino groups are basic. They
will become ionic when reacted with an acid because
the lone pair on the nitrogen atom becomes bonded
to a proton which creates an ionic substance.
H
Cl
N
H2O
H
H
Covalent amino compound
insoluble in water
H-Cl
N
H
H
Ionic compound is
soluble in aqueous
acid solution!
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So, what would you expect for the behavior of
ethyl 4-aminobenzoate in acid solution and basic
solution?
O
H2N
C
O
CH2 CH3
Ethyl 4-aminobenzoate
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Remember This…
• Ionic compounds are usually very
soluble in water. Consider Na+ Cl• Higher molecular weight compounds
with covalent bonds are usually
insoluble in water
• If the covalent compound can be
converted to ions, it will dissolve in
aqueous solution!
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Part E. Critical Thinking
Application
• Skip this section
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Experiment 3: Crystallization
• Reading Assignment:
–
–
–
–
–
–
Experiment 3 (pp. 21-32)
Technique 6 (pp. 589-597)
Technique 7 (pp. 598-616)
Technique 8 (pp. 616-627)
Technique 9 (pp. 627-637)
Technique 11 (pp. 647-668)
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Experiment 3
• Note that this is a two-day experiment
• Plan on using your time as follows, or
as your instructor suggests:
– First day: Part A and part B
– Second day: Part C
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Experiment 3
• NOTE CAREFULLY:
– Although the textbook does not say to
submit your samples with your
laboratory report, the laboratory report
sheet does!
– Be sure to submit your purified samples
of sulfanilamide and fluorene in separate
labeled vials.
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Experiment 3
• If you do not obtain 150 mg of
sulfanilamide crystals for Part A or 45
mg of crystals for Part B, expect to
repeat the procedure until you get it
right.
• The key is to figure out how to get
crystals to form using the minimum
amount of solvent.
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Experiment 3
• There is a pre-lab exercise that is due to
your instructor before beginning this
experiment. The 4th edition of the
textbook doesn't have the data for
sulfanilamide (although you could
guesstimate from the graph on page 648,
figure 11.2). Use the following data,
instead:
• 0 deg -- solubility 14 mg/mL
• 20 deg -- solubility 24 mg/mL
• 40 deg -- solubility 46 mg/mL
• 60 deg -- solubility 88 mg/mL
• 78 deg -- solubility 210 mg/mL
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Consult your section’s syllabus for the due date for
post-laboratory report.
Remember to submit the samples with your
laboratory report!
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• Part A. Semimicroscale
Crystallization
– Use an Erlenmeyer flask and Hirsch
funnel
• Part B. Microscale Crystallization
– Use a Craig tube
• Part C. Selecting a Solvent to
Crystallize a Substance
• Part D. Critical Thinking
Application
– Skip this section
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O
H2N
S
O
NH2
Sulfanilamide
m.p. = 165 - 167°
Fluorene
m.p. = 114 - 116°
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Semimicroscale crystallization
using vacuum filtration: Part A
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Microscale crystallization using a
Craig Tube: Part B
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Craig Tube + Centrifuge Tube
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Solubility – Types of Solutions
Saturated: The solution contains the maximum
amount of solute that it can hold at that
temperature. No more solute can be dissolved.
Unsaturated: The solution contains less than the
maximum amount of solute that it can hold at that
temperature. More solute can be dissolved.
Supersaturated: The solution contains more solute
than the maximum amount of solute that it can
hold at that temperature. A supersaturated
solution is unstable; a precipitate (or crystals) is
likely to form if the solution is disturbed.
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Crystal Formation
• A dissolved material will separate from
the solution as it is cooled.
• If the crystal growth is slow and
selective, that is crystallization
• If the crystal growth process is rapid
and nonselective, that is
precipitation.
• In crystal growth, molecules arranged
themselves into a highly specific
structure called a crystal lattice.
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Crystal Formation
• A successful crystallization depends on a
large difference between the solubility of a
material in a hot solvent and its solubility
in the same solvent when it is cold.
• A material can be purified by crystallization
when both the desired product and the
impurity have similar solubilities, but only
when the impurity represents a small
fraction of the total solid.
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Solubility versus Temperature
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Solubility of Sulfanilamide in
95% ethanol-water
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What Are The Characteristics of a
Good Crystallization Solvent?
• There should be a large difference in
solubility between hot and cold solvent
• The boiling point of the solvent should be
well below the melting point of the solute.
• The solvent must not react with the solute
• The solvent should have a low boiling point
(makes removal of the solvent easy)
• The solvent should be non-toxic
• The solvent should be innocuous
• The solvent should not be expensive
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Crystallization: Technique
• You should always do a crystallization
in an Erlenmeyer flask or in a Craig
tube.
• Do not use a beaker or a roundbottom flask for crystallization.
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Semi-microscale Crystallization
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Good Laboratory Practice
• When you isolate crystals, allow them
to air dry overnight.
• Wait until the following day to
determine the weight or the melting
point.
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Determining Melting Points
• READ: Technique 9 (pp. 627 – 637)
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Melting point-Composition Curve
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Melting point
Normal expectation for the melting point of an impure
compound:
1. The melting point will be low compared to the literature
value.
2. The melting point is never a single number! You will
observe a range from when it starts to melt to when
it has melted completely.
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Mixture Melting Points
•
The melting point can be used in
identifying a compound.
1. One can compare the melting points of
a known and an unknown compound.
2. If an unknown solid is mixed carefully
with an equal amount of known
compound, one can then determine the
melting point of the mixture
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Mixture Melting Points
• If the melting point of the mixture is
identical to the melting points of the
two separate substances, we may say
that the two substances are identical.
• If the melting point of the mixture is
depressed, it is clear that the known
and the unknown are different
substances.
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