chemistry xxi lab session 13 how do we synthesize new substances? (two-week experiment)
TRANSCRIPT
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Lab Session 13
How do we synthesize new substances?
(Two-Week Experiment)
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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.
Before We Start What do you think?
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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.
Instructor & Course Evaluation
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The End is Near(ing)9 10 11
VTs DayNo classes
12 13 VTs DayMake up
16CHEM 151
Exam 3
17 18 19Final day to
do lab
20
23No Labs
24No Labs
25No Labs
26ThanksgivingNo classes
27No classes
30
Lab FinalsWeek
1DecemberLab Finals
Week
2
Lab FinalsWeek
3
Lab FinalsWeek
4
7CHEM 151
Exam 4
8 9 Last Day
10DEAD DAYNo Classes
11FinalsBegin
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What are we doing?
Last week we started exploring some techniques used to “synthesize” new substances.
TransformationHow do I change it?
AnalysisWhat is this?
ModelingHow do I explain it?
SynthesisHow do I make it?
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IYour Challenge
Imagine that you work for a drug company interested in testing a new procedure to
synthesize aspirin.
You have been asked to evaluate whether the procedure is feasible and marketable.
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Initial IdeasIn your groups, summarize what you did last week and the results that you got.
Acid Catalyst
What was your percent yield?What problems did you encounter?
What do you still need to do?
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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.
Purity
How do you plan to assess the purity of your product. What techniques would be
useful?
Melting point, TLC, and Titration
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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:
Melting Point Are there impurities?
TLC How many?
Titration How Much?
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In your groups:
Define melting point
Define melting point range.
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.
Melting Point
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Safety Precautions
The melting point device can get very hot. Be careful to not burn yourself.
The thermometer must not be left in the melting point device once measurements have been made.
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Two different ones:
Closed-ended tubes are for melting point.
Open ended tubes are for TLC.
Do not mix them up!
Don’t forget – they’re GLASS WASTE!
Capillary Tubes
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TLC
In your groups:
Define TLC.
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.
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Seeing Spots
Unlike the TLC of spinach leaf extract, the aspirin is colorless.
Two methods will be used to make the spots visible.
What are the the two methods?
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Seeing Spots Safely
Iodine – Stains the skin. Fumes are acrid
UV Light – Can damage the
retina. Avoid looking at
the lamp.
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First Challenge
Analyze the purity of your product using Melting Point determination and
TLC analysis.
Available resources:
Melting point apparatus
TLC plates.TLC plates.
SolventSolvent
Your aspirin
reagent grade aspirin and an reagent grade aspirin and an aspirin tablet. aspirin tablet.
You have 60 minutes
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Claims and Evidence
Based on the results, present your major claims about the purity of your product.
Are their claims clear?
Is the evidence reliable?
Is the evidence appropriate to support the claims?
How do you explain the results?
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How much is there?
C9H8O4 + NaOH C9H7O4Na + H2O
Sodium Acetyl
Salicylate
Sodium Hydroxide
Acetyl salicylic
acid (Aspirin)
Water
We can quantify how much Aspirin is there by making it react with a known amount of another
substance (NaOH):
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.
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Titration
Unknown Amount
nu
Known concentration
CAt the endpoint of a titration,
the moles of known added equals the moles of unknown
in the sample (if 1:1 ratio).
nu = VfC
Measured Vf
End point
Indicator(signals
endpoint)
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The Buret
Time for a demonstration
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Final Challenge
Titrate a small sample of your aspirin to analyze its purity.
You have 60 minutes
Available resources:
Standardized solution of NaOH;
Glassware;
Buret;
Phenolphthalein indicator .
Titrate a part of your aspirin tablet.
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How much is there?
C9H8O4 + NaOH C9H7O4Na + H2O
Sodium Acetyl
Salicylate
Sodium Hydroxide
Acetyl salicylic
acid (Aspirin)
Water
Based on your results, and on this titration equation, calculate the actual
percent of aspirin in your sample.
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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?
Is the evidence reliable?
Is the evidence appropriate to support the claims?
How do you explain the results?
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What did you learn from doing your experiment?
How would you improve what you did?
How have your ideas changed as a result of this lab?
What do you not completely understand?
What new questions do you have?
Final Reflections
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Beginning questions (2 p);
Safety Considerations (2 p);
Procedures and Tests (2 p);
Data, calculations, and representations (6 p);
Claims (2 p);
Evidence and Analysis (6 p);
Reflections and additional questions (10 p).
Your Report
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• 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)?
In Your Report
Your report should provide answers to these questions: