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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: