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The following is a list of things you should bear in mind when you
compose a lab report using Microsoft’s Word program: 1. Use 12
point font with normal (1") margins on all sides. 2. Number all
pages in sequential order. 3. The date shall be the actual date when
your experiment was performed. 4. Separate sections with
appropriate sub-headings (bold or italic); and staple all pages
together. 5. Your and your partner’s names must be on the report in
the following format:
XXX (your name)
Partner: YYY (partner name) 6. If it’s an experiment of technique
(such as melting point measurement), show the chemical structures
for all the compounds you actually used in the experiment. If it’s a
reaction, show the reaction scheme but not individual structures in
the first page. You must draw the structures/schemes by yourself
using appropriate software such as MarvinSketch, Accelrys, or
ChemDoodle. Direct copy of images from your eChapters, Internet
or any electronic resources is not allowed. 7. For reference specify
the edition and full page range of the lab textbook. (This
requirement is different from the example section F on page 21 of
the textbook.) 8. For scientific report the smallest details, such as
punctuation, need to be as accurate and correct as possible.
Convention must be followed. The grammar must be checked.
Each occurrence of minor error will result in 5 points reduction.
You will receive some leniency for first-time mistakes, but each
recurring minor error will result in full 5 points deduction.
9. All measured values must have an appropriate unit. Have one
o
space between any value and its unit, such as 132 – 133 C. Use
o
symbols/abbreviations for the units, such as C instead of degree
Celsius and g instead of gram. Common units: g, mg, mol, mmol,
o
mL, L, C, mm, cm, m, h (for hour), min (for minute), s (for
second). The values should also have correct significant numbers.
Thus 0.1350 g (measured from a balance) should not be recorded
as 0.14 or 0.135 g, and 1.04 mL (measured from a graduated
cylinder) should not be recorded as 1.0 or 1 mL.
10. Chemical names are like other nouns. Don’t capitalize them
unless they are at the beginning of a sentence. Unlike elsewhere in
a sentence, there should be no space after a comma in chemical
names, e.g. 1,2-dichloromethane. This is a convention for
chemists. Similarly, it should be “iron(III) chloride” but not “iron
(III) chloride”. The atom symbols in chemical names needs to be
capitalized and italic, such as N,N-dimethylaniline. Prefixes such
as “tert”, “meta”, “m”, “ortho”, and “para” need to be italic as in
“t-butyl chloride” or “m-xylene”, and they are not capitalized at the
beginning of a sentence, e.g. “m-Xylene was used...”.
Page 1
11. Procedure: Rephrase the procedures in the textbook using past
tense (the action was already done) and passive voice (focus on the
action not the doer) for the lab reports. This requirement is
different from the example section I on page 22 of the textbook.
Quite often we made omissions/additions/modifications to the
procedures on the textbook, and in your lab report you should write
only the modified procedures. You can write up simplified steps
for pre-labs (R on page 25 of the textbook) but only normal
paragraphs (see I-K on page 22) should be adopted for lab reports.
Wrong format in your Procedure section will result in 10 points
deduction.
Wrong: Crush the sample into fine powder using a spatula.
(instruction format, present tense) Wrong: We crushed the sample
into fine powder using a spatula. (active) Correct: The sample was
crushed into a fine powder using a spatula. (past tense, passive
voice)
12. Observations: faithfully record what you actually did in the
experiment. Any data (weight, volume, temperature, time, etc.) and
phenomenon (color change, cloud, smoke, bubbling, heat
generation, etc.) must be reported. Do not repeat what was already
said in the “Procedure” section, although you may have to briefly
mention which part of the procedure it was in relation to the
observation. Report any accidents and spills. Past tense and passive
voice should be used.
13. Yield calculation: for chemical reactions you must show the
balanced equation, determine the limiting reagent, and calculate
the theoretical and actual yields. The quantity of the starting
materials should be what you actually measured (such as 76.9 mg)
but not just what the textbook says (such as 75 mg). The yields
should be rounded to an integer, e.g. 53% instead of 52.88% or
52.9%. Yield calculation which is wrong or lacking details will
result in up to 20 points reduction. The yield you get will not affect
your report grade significantly. Too high (> 100%) or too low (<
30%) yield will result in 10 points reduction, in which case you
should rationalize it in the “Discussion and Conclusions” section.
14. The reaction mechanism should be drawn by software (such as
MarvinSketch, Accelrys, or ChemDoodle) if it has been discussed
during our lectures or in in your lab textbook.
15. Discussion and Conclusions You can include things like
trends in the data, data interpretation, relevance of the
experiment or the technique, and what you have learned. To
elaborate using an example:
Background material. Define melting range. What
happens on a molecular level during melting?
Data trends and interpretation. Any trends on the data?
Is the data as expected? Explain the theory and principle
behind the expected trend in the data. If it is not, what are
sources of errors? o The melting point (mp) we obtained
for pure urea is which is close to the literature value of .
Page 2
o Mixtures have lower mp and broader mp range than the pure
substances because . Our data is as follows:
and is
consistent with this expected
result.
What would be an application of this technique or data
trend? (e.g. identification,
determination of purity) Summarize the success (or failure) of the
experiment. Describe what happened in your
experiment. Describe the interpretation of the results and their
significance. Explain what the results mean, what conclusions can
be drawn, etc. Do not put excessive focus on yield. You can simply
mention your yield as low/high/moderate/reasonable and briefly
discuss the possible reasons for that outcome. Your data should be
presented in the form of tables and graphs as appropriate. All
tables and graphs must be well-organized, numbered, and given
clear descriptive titles. (e.g. Graph 1. Mp-Composition Diagram
for Urea/Cinnamic Acid Mixtures.)
Do not simply repeat your procedure and observations in this
section. This is probably the most important section of your lab
report. Deficiencies in this section will result in up to 30 points
deduction from your lab report grade.
16. A good discussion of lab report writing can be found at
http://www.professorkshow.com/sample-organic.html. If there is
any contradiction to my instructions as above, follow my
instructions.
Page 3
How to calculate the yield of an organic reaction?
Sample reaction: borohydride reduction of 2methylcyclohexanone. Make sure you have the balanced reaction
written out:
O OH CH3
3
+ NaBH4 3 112.17 37.83
MW (g/mol)
114.18
The theoretical yield must be calculated based on the actual
quantity of the starting materials you used. If the textbook
mentions something like “The residue should weigh about 150
mg”, you cannot use that 150 mg as your theoretical weight of
your product.
According to the textbook instructions, you should use 300 mg of
2-methylcyclohexanone and 50 mg of sodium borohydride. Let’s
suppose you get 0.2343 g of product in the end.
Scenario 1: you indeed used exactly the quantities as indicated in
the textbook. 2-methylcyclohexanone: 0.300 g ÷ (112.12 g/mol) =
0.00268 mol NaBH4: 0.050 g ÷ (37.83 g/mol) = 0.00132
mol Notice from the balanced reaction 0.00268 mol of 2methylcyclohexanone would
consume 0.00089 mol of NaBH4. You actually used 0.00132 mol
of NaBH4, so it is in excess and 2-methylcyclohexanone is the
limiting reagent.
The mole ratio between the products (a mixture of cis and trans
isomers) and 2- methylcyclohexanone is 1:1, so the theoretical
weight of the products is:
2-methylcyclohexanol: 0.00268 mol × (114.18 g/mol) = 0.301 g
The actual yield you got is:
(Notice the example calculation M on page 23 of the lab textbook
contains one error. It should be 100% but not 100 in the equation.)
Scenario 2: you actually used 0.303 g of 2-methylcyclohexanone
and 0.034 g of NaBH4. 2-methylcyclohexanone: 0.303 g ÷ (112.12
g/mol) = 0.00270 mol NaBH4: 0.034 g ÷ (37.83 g/mol) = 0.00090
mol Notice from the balanced reaction 0.00090 mol of NaBH4
would consume exactly
0.00270 mol of 2-methylcyclohexanone. So both starting materials
are the limiting reagent. If you choose to use NaBH4 as the
limiting reagent, the ratio between the products to
NaBH4 is 3:1, so the theoretical weight of the products is: 2methylcyclohexanol: 0.00090 mol × 3 × (114.18 g/mol) = 0.308
g (If you choose to use 2-methylcyclohexanone as the limiting
reagent, the ratio between
the products to 2-methylcyclohexanone is 3:3, or 1:1, so the
theoretical weight of the products still is:
2-methylcyclohexanol: 0.00270 mol × (114.18 g/mol) = 0.308 g)
Page 4
The actual yield you got is:
Scenario 3: you actually used 0.303 g of 2-methylcyclohexanone
and 0.030 g of NaBH4. 2-methylcyclohexanone: 0.303 g ÷ (112.12
g/mol) = 0.00270 mol NaBH4: 0.030 g ÷ (37.83 g/mol) = 0.00079
mol Notice from the balanced reaction 0.00079 mol of NaBH4
would consume 0.00237 mol
of 2-methylcyclohexanone. You actually used 0.00270 mol of 2methylcyclohexanone, so it is in excess and NaBH4 is the limiting
reagent.
The ratio between the products to NaBH4 is 3:1, so the theoretical
weight of the products is:
2-methylcyclohexanol: 0.00079 mol × 3 × (114.18 g/mol) = 0.271
g The actual yield you got is:
0.2343 g
x 100% = 86%
Your experiment will always fall into one of the above three
scenarios when you run any two- component reactions. Make sure
to show the calculation and reasoning process as above for your
lab reports. Wrong yield calculation will result in 10 points
deduction from your lab reports.
0.271 g
Page 5
Chapter 41. Synthesis of Acetylsalicylic Acid (Aspirin)
O
O
OH
OH
+
H3C
O
C
O
O
C
H3PO4
CH3
©Dr. Wang
OH
O
C
O
CH3
+
H3C
O
C
OH
Roles of chemicals
salicylic acid: reactant/starting material
acetic anhydride: reactant & solvent
85% phosphoric acid: catalyst
aspirin: desired product
acetic acid: by-product
All the above chemicals are strongly acidic and corrosive. Be careful of their handling.
Modified procedure:
One person can prepare the water bath while your partner is weighing/getting the chemicals. A
thermometer needs to be securely placed in the water bath, and the bath temperature could be in
the range of 85 to 95 oC. Use the spirit thermometer if you have one. The bulb of thermometer
could loosely touch the bottom of the beaker while the top of thermometer is held in place by a
clamp. Use a smaller beaker (100 mL) with half full of tap water to generate the water bath. Note
that the hot plate temperature setting needs to be higher than 95 oC. You could start from 200 oC
and adjust it gradually to achieve ~90 oC water bath temperature.
When you weigh salicylic acid (a solid), any mass between 0.1350 to 0.1450 g is
acceptable and you don’t have to get exactly 0.1380 g (or 138.0 mg). Make sure you
don’t take too much out of the reagent bottle. Record the exact mass on your notebook
and use it for yield calculation after the lab. If you get more salicylic acid than you
need, throw it into the solid waste container. Do not put the excess back into the salicylic
acid reagent bottle.
The amount of acetic anhydride does not need to be very accurate. (Discuss why in your
lab report.) Mostly conveniently it can be measured in a small reaction tube more than
half way toward the 0.5 mL mark. Because acetic anhydride is strongly corrosive and has
a bad sour smell, the reagent bottle must be capped immediately after your measurement.
To a reaction tube, add ~0.14 g of salicylic acid, a boiling chip, one drop of 85% phosphoric acid,
and ~0.3 mL of acetic anhydride. Add the liquid acetic anhydride from the top of the reaction
tube in a circular and slow motion to wash all solid down to the bottom of the tube. Mix the
reactants thoroughly with a spatula and heat the reaction tube in the 90 oC water bath for 5
minutes. A transparent solution should form, however the boiling stone will apparently not
dissolve. Take the reaction tube out of water bath, let it cool to room temperature, add ~0.5 mL
of water, and thoroughly mix all liquids with a spatula. Water serves to destroy the unreacted
acetic anhydride and provide a suitable solvent system for aspirin to crystallize out. Let the
mixture sit at room temperature for 5 min and note the shape and color of the crystals. If
crystallization of the product does not occur, scratch the liquid-air interface inside the tube with a
1
glass stirring rod until you begin to see the formation of tiny crystals. Further cool the tube in an
ice/water bath for 10 min.
Fit a filter paper in the Hirsh funnel, wet it with a few drops of water, and set up the vacuum
filtration apparatus. The filter flask should be secured by a clamp to prevent the system from
being tipped over. Using as much icy water as needed, transfer all solid inside the tube onto the
wet filter paper. Use the spatula to pick up the boiling stone and rinse it with a few drops of icy
water. Throw the boiling stone into the normal trash. Perform vacuum filtration and dump all the
filtrate down the drain. With vacuum off, break big chunks of solid down to small pieces, and
wet the crystals with 5 drops of ethanol using a Pasteur pipette. (Caution: if you use excessive
ethanol you could lose all your product. Never directly squeeze the ethanol solvent bottle to get 5
drops.) Then turn the vacuum on for 5 min and let the wind constantly pass through the solid to
remove all the residual liquid chemicals including acetic acid, water, and ethanol. The final
product must appear loose and dry. Record its appearance including color and texture (white
power, colorless needle-like crystals, etc.). Weigh the final product and submit it to Dr. Wang for
IR analysis.
After IR analysis dispose of your aspirin product (excluding the weighing paper) into the
solid waste container.
All your used glassware should be washed with soap water and then rinsed with small
amount of acetone twice. Clean up all your bench area and hood. Fully close the hood
sash all the way down before you leave.
Discussion of the reaction mechanism and side reactions can be skipped in your lab
report. Compare the IR spectrum of your product to that of the starting salicylic acid and
make conclusions on whether your reaction worked or not. Your IR spectrum of aspirin
(solid alone) may be somewhat different from FIG. 41.1 on page 532 (solution in CHCl3)
but should be reasonably close. Consult your Organic Chemistry lecture textbook and
explain key characteristic peaks in your IR spectrum. Attach the product IR spectrum to
your lab report.
Yield calculation is mandatory for all reactions. Consult the example included in “Lab
Report Instructions” in Blackboard. As a reminder, you must calculate the mole amounts
of all reactants (but not catalyst) and compare them to find out the limiting reactant.
Because acetic anhydride is a liquid, you need to find its density using Internet. Note that
mass = density x volume, and mole amount = mass ÷ molecular weight.
2
Acetylsalicylic Acid (Aspirin,
Purpose: synthetise A cetylsalioylic Acid. caspirin)
date
0 GOH
o
LOH
control
요
4
roderi
CH₃
Q=0
он
+ H3C co
atz
+
CH₃
Ho
Reference
Williamson and saasters
and masters , Macroscale and Microscale Organic
Experiment page
:
ed.
Table of Quantities
o
oc
G/mol used
on produced
Subtance
And wt
Salicylic acidl 138.12
acetic anhydride 102.09
Mol Needed
(from og.) Density mp bp Solutiting
soluble in
ether
1.4439/ml 188.6 200 colu
benzene
soluble
1,0828/cm² -73.1 137.8 Werter
Miscible
acetic acid
11049g/cm3 16-17 118 119 verter
60105
soluble
1145/cm3
B6 140
180.158
in
warter
aspirin.
side reactions
observation
Procedure 1/24/2018
Prepare waiter berth, use a smaller
beaker (room) with half full of tap
the worker berth!
water
to generate
b setrie
weighing chemicals : Salicylic acid.
811350 - 0.1450 g.
acetic anhydride
small tube disul mark
7m{0
า
3
ab
20
os lock
olt
ord
er
the solvent went worbiel.
transparent
white floccule
white floccule
Come crystals
of tube
ou
the wall of
add
~0:14 Salicylic acid, a
bolihing chip, one drop 85% tapau
Nasonl acetic anhydride
(from top of the tube in a cicular)
heat for Smin in 90°c weiter
bath.
take out tube. let it cool. add
noisml water mix thoroghtly
sit for 5min in room temp
(note sheipe and color of crystals)
Cooling tube in Ice/nenter bath for
lomin
Fit a filter paper in Hirsh funnel.
met it with water and set up
the vacuum filtrertion apparatus
transfer all solid inside the tube onto
to pick up the boling stone and
rinse se with icy water. Throw
the stone in noranl trash
Perform vacuum filitrertion and dump
all the filtrate down the drain.
with vacuum off, break big chunks
of soild down to small pieces, and
wel the cystals with 5 drops of
ethanol using pasteur prpette
Spatula
white powder
.
spilled some product
.
Turn the racuum for 5 min. let
Wind through solid, remove all
chemicals.
( Record se appearance / color / texture.)
& weish product and submit to Drway.
5
white powder
0.2950