GenChem
Week 5
Chemical Synthesis
Second week of a three-week experiment
Today’s Agenda:
 Review of chemical syntheses and yields.
 Discussion of recrystallization
 Performing recrystallization.
 Determining melting point.
 Determining unreacted salicylic acid
 Thin layer chromatography (next week).
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Chemical Synthesis: Review
In your groups,
summarize what
you accomplished
last week.
Do you have dry
aspirin? If so, how
much? Do you
have your %
yields?
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Let′s think!
What’s
next? Can
we putpurification
our crude
The
government
will require
and testing
before
can market.
aspirin
intowe
tablets?
What kind of chemical analysis is
purification?
How are we going to achieve it?
• separation
• precipitation
Let′s think!
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Recrystallizing Aspirin
In your groups review your
responses to the following
pre-lab question and come up
with a consensus answer.
Using the Summary of Steps given in chapter 7 of the
lab book as a guide prepare a set of directions for
performing the recrystallization. Make sure to include
all the materials and equipment you expect to use.
Let′s think!
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Assessing purification
How can we know how
effective our purification
procedure is?
In your groups discuss how you would
go about determining how effective
your purification of your aspirin is.
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Experiment Flow
If you have 0.4 g or more of aspirin, divide your
aspirin in half and mass each portion. (If you don’t
have 0.4 g, consult your TA)
Save half as crude product.
THIS WEEK
Determine melting point
NEXT WEEK
Perform TLC
RECRYSTALLIZE half and
save as purified product.
THIS WEEK
Determine melting point
NEXT WEEK
Perform TLC
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Chemical
Synthesis
Pre-lab
quiz questions
class results
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Let′s explore!
First Challenge
Divide your product in half.
Recrystallize half your aspirin
product.
Available resources:
 ethanol
Use your procedure as
modified here in class.
 glassware
 ice bath
 hot plate
You have
30 minutes
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Now for the
Qualitative
Question.
How pure is
your aspirin?
Your problem is to assess the purity of your
aspirin with the intent of making the argument
that it is pure enough to market.
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What methods will you use to
assess the purity of your
aspirin?
• melting point
• TLC
Let′s review!
Melting Point
Determination
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In your groups answer the
following
• define melting point
• define melting point range.
• explain why it can be used to
identify a substance.
• explain how it can be used to
determine the purity of a
substance.
• outline the steps required to
obtain a melting point range
using the Mel-temp.
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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.
Let′s review!
Capillary Tubes
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Two different ones:
• closed-ended tubes
are for melting point
which you will do today.
• open ended tubes are
for TLC which you will
do next week.
• do not mix them up!
• & don’t forget – they’re
GLASS WASTE!
Let′s explore!
GenChem
Melting Point Challenge
Melting Point Determination
Available resources:
 Melting point apparatus (one
devices per group of four).
 Your aspirin
When you have a
melting point
range for your
product, report it
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Let′s explore!
TLC Challenge
Thin Layer Chromatography
This Challenge will be performed
next week.
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Introduction
• From p. 65 of your Technique Book:
Introduction. A description of what is already
known, the plan of action and expected
outcomes.
• From p. 71 of your Technique Book:
Introduction. A description of:
• the experimental objective(s)
• pertinent background information
• expected outcomes, if any
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Introduction: Helpful hints
• Only include information that is known before
lab. No results, observations, etc.
• 200 word maximum for one week lab.
• Paragraph format. Subheadings okay.
• Give items in context. No lists.
• See Technique Book pp. 65, 67 and 71 for
more help with writing an Introduction
• See Technique Book pp. 52-55 for more help
with scientific writing.
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Thinking about
the Report
Things you will need to
consider when you
write your report.
Due in two weeks.
Discussion
• Discuss your yield of aspirin.
Is it a good yield? Defend
your opinion.
• How pure is your aspirin?
Discuss whether or not your
aspirin is pure enough to be
consumed.
• Can your yield be improved
upon? How and where?