Chemistry XXI
Lab Session 13
How do we synthesize
new substances?
(Two-Week Experiment)
Before We Start
What do you think?
Chemistry XXI
Instructor & Course Evaluation:
In the past we have found our
students’ remarks and
suggestions to be very helpful.
This input has led to a number
of changes in our experiments
and our programs. For the
benefit of future students we
ask for your thoughtful
comments.
Instructor & Course Evaluation
Chemistry XXI
Please be as specific as possible and
keep the following in mind:
A. This information will be used not
only to evaluate your instructor but
also to evaluate the course.
B. Your instructor will not be allowed
to see your comments until AFTER
grades have been submitted to the
Registrar.
C. ALL evaluations are read by at least
three members of the department.
D. We need to know what we are doing
right as well as how we can improve.
The End is Near(ing)
9
10
11
12
13
VTs Day
Make up
19
Final day to
do lab
20
Chemistry XXI
VTs Day
No classes
16
CHEM 151
Exam 3
17
23
No Labs
24
No Labs
30
1
December
Lab Finals
Week
Lab Finals
Week
7
CHEM 151
Exam 4
18
25
No Labs
26
27
Thanksgiving No classes
No classes
2
Lab Finals
Week
8
4
Lab Finals
Week
9
Last Day
3
10
DEAD DAY
No Classes
11
Finals
Begin
What are we doing?
Analysis
What is this?
Synthesis
How do I make it?
Chemistry XXI
Transformation
How do I change it?
Modeling
How do I explain it?
Last week we started exploring some techniques
used to “synthesize” new substances.
Your Challenge
Imagine that you work for a drug company
interested in testing a new procedure to
synthesize aspirin.
Chemistry XXI
You have been asked to evaluate whether the
procedure is feasible and marketable.
Initial Ideas
In your groups, summarize what you did
last week and the results that you got.
Chemistry XXI
Acid
Catalyst
What was your percent yield?
What problems did you encounter?
What do you still need to do?
Purity
Chemistry XXI
Your central problem this week is to
assess the purity of your aspirin with the
intent of making the argument that it is
pure enough to market.
How do you plan to assess
the purity of your product.
What techniques would be
useful?
Melting point, TLC, and Titration
Different Tests
Why do we need to perform three different
tests to analyze the purity of our product?
The test allow us to answer different
questions:
Chemistry XXI
Melting Point  Are there impurities?
TLC  How many?
Titration  How Much?
Melting Point
In your groups:
 Define melting point
 Define melting point range.
Chemistry XXI
 Explain why melting point can
be used to identify a substance.
 Explain how it can be used to
determine the purity of a
substance.
 Create an outline of the steps
required to obtain a melting point
range using the Mel-temp7.
Safety Precautions
 The melting point device can get very hot.
Be careful to not burn yourself.
Chemistry XXI
 The thermometer must not be left in the
melting point device once measurements
have been made.
Capillary Tubes
Two different ones:
 Closed-ended tubes are
for melting point.
Chemistry XXI
 Open ended tubes are
for TLC.
 Do not mix them up!
 Don’t forget – they’re
GLASS WASTE!
TLC
In your groups:
 Define TLC.
Chemistry XXI
 Explain how TLC can help
confirm that you really made
aspirin.
 Explain how TLC can be used
to determine the purity of your
aspirin.
 Create an outline of the steps
required to successfully
chromatograph the three
samples.
Seeing Spots
Unlike the TLC of spinach leaf extract, the
aspirin is colorless.
Chemistry XXI
Two methods will be used to make the spots
visible.
What are the the
two methods?
Seeing Spots Safely
Chemistry XXI
Iodine –
Stains the skin.
Fumes are acrid
UV Light –
Can damage the
retina.
Avoid looking at
the lamp.
First Challenge
Analyze the purity of your product using
Melting Point determination and
TLC analysis.
Available resources:
 Melting point apparatus
Chemistry XXI
 TLC plates.
 Solvent
Your aspirin
 reagent grade aspirin and an
aspirin tablet.
You have 60
minutes
Claims and Evidence
Based on the results, present your major
claims about the purity of your product.
 Are their claims clear?
Chemistry XXI
 Is the evidence reliable?
 Is the evidence appropriate to support the
claims?
 How do you explain the results?
How much is there?
We can quantify how much Aspirin is there by
making it react with a known amount of another
substance (NaOH):
C9H8O4 + NaOH  C9H7O4Na + H2O
Chemistry XXI
Acetyl
salicylic
acid
(Aspirin)
Sodium
Hydroxide
Sodium
Acetyl
Salicylate
Water
If we determine the moles of NaOH that react, we
can determine the mass of Aspirin present in the
sample. The process is called Titration.
Titration
Chemistry XXI
Known
concentration
C
At the endpoint of a titration,
the moles of known added
equals the moles of unknown
in the sample (if 1:1 ratio).
Measured
Vf
Unknown
Amount
nu
Indicator
(signals
endpoint)
nu = VfC
End point
Chemistry XXI
The Buret
Time for a
demonstration
Final Challenge
Titrate a small sample of your
aspirin to analyze its purity.
Available resources:
Chemistry XXI
 Standardized solution of
NaOH;
 Glassware;
 Buret;
 Phenolphthalein indicator .
Titrate a part
of your
aspirin
tablet.
You have
60 minutes
How much is there?
C9H8O4 + NaOH  C9H7O4Na + H2O
Chemistry XXI
Acetyl
salicylic
acid
(Aspirin)
Sodium
Hydroxide
Sodium
Acetyl
Salicylate
Water
Based on your results, and on this
titration equation, calculate the actual
percent of aspirin in your sample.
Claims and Evidence
Based on the results of ALL of your tests,
present your major claims about the
purity of your product.
 Are their claims clear?
Chemistry XXI
 Is the evidence reliable?
 Is the evidence appropriate to support the
claims?
 How do you explain the results?
Final Reflections
 What did you learn from doing your
experiment?
 How would you improve what you did?
Chemistry XXI
 How have your ideas changed as a result
of this lab?
 What do you not completely understand?
 What new questions do you have?
Your Report
 Beginning questions (2 p);
 Safety Considerations (2 p);
 Procedures and Tests (2 p);
Chemistry XXI
 Data, calculations, and representations (6 p);
 Claims (2 p);
 Evidence and Analysis (6 p);
 Reflections and additional questions (10 p).
In Your Report
Your report should provide answers to
these questions:
Chemistry XXI
• Is this process feasible and marketable?
What is your evidence?
• How much would it cost to produce a
500 mg aspirin tablet using this method?
• How could improve the process (Feasibility
and Marketability)?