Seton Hall University Organic Chemistry Recrystallization Lab Report

Name:Exp # 1
Date:
Lab Partner
Title: Recrystallization of Naphthalene
1. Abstract and Purpose: (2 point).
Recrystallization of solids is one of the most common methods used to purify solids. The
process of recrystallization involves dissolving the solid in an appropriate solvent at an
elevated temperature and allowing the crystals to re-form on cooling, so that any
impurities remain in solution. (In this paragraph, we define and explain the key concept
discussed in this lab).
In this lab, we will be exploring ways to purify impure naphthalene by recrystallization
(What is the specific experiment you carry out?), and learn how to choose a good solvent
system, how to carry out decolorization and how to induce crystallization. Common
technique such as hot gravity filtration, vacuum filtration and melting point determination
will be practiced in this lab session. (What are the techniques or lessons you learn
through this experiment?)
2. Balanced equation: (2 point)
In organic chem, there are different types of experiments: technique and preparative. A
technique experiment is one in which you are performing a technique for the first time
and studying its details, for example, recrystallization, distillation and extraction. A
preparative experiment is one in which a compound is synthesized from other reagents.
Balanced equation for the reaction is needed only if the experiment is a preparative
experiment.
Name:
Exp # 1
Date:
Lab Partner
There are several free structure drawing programs available e.g. acdlabs.com. If you
don’t have a drawing program, hand draw the structures.
3. Reagent Table (Add more rows when needed) (3 points)
Name
M.W.
(g/mol)
Density*
(g/mL)
M.P.*
(°C)
B.P.*
(°C)
Amount
(grams
or mL)
Moles
(mmol)
Hazards/Precautions
Naphthalene
128.17
1.085
80 82 °C
218 °C
~1 g*
7.81*
Flammable solids,
Acute toxicity,
Carcinogenicity, Acute
and chronic aquatic
toxicity
Ethanol
46.07
0.789
-114 °C 78 °C
Hexane
86.18
Toluene
92.14
0.865
Acetone
58.08
0.791
Highly flammable,
Eye irritation
110 111 °C
Flammable liquids
Skin irritation
Reproductive toxicity
Specific target organ
toxicity
Aspiration hazard
Acute and chronic
aquatic hazard
-93 °C
110 111 °C
Flammable liquids
Skin irritation
Reproductive toxicity
Specific target organ
toxicity
Aspiration hazard
Acute aquatic toxicity
-94 °C
56 °C
Flammable liquids
Eye irritation
Specific target organ
toxicity
Name:
Exp # 1
Date:
Lab Partner
Activated
charcoal
12.01
1.8 – 2.1
3,550 °
C
N/A
Celite
60.08
N/A
N/A
N/A
May form
combustible dust
concentrations in air
N.B. For solvents (like ethanol) or drying agents (e.g. sodium sulfate), you don’t
need to calculate the moles.
* Report only when applicable
* Mass and moles may change depending on the exact weight measured in lab.
4. Calculations: Shown each calculation for moles of reagents, limiting reagent,
theoretical yield and percent yield. (4 points)
Calculating moles of naphathalene:
Determining limiting reagent: N/A
The limiting reagent is N/A
Calculating theoretical yield: N/A
The theoretical yield is N/A
The actual yield is N/A
Calculating Percent yield: N/A
Reaction percent yield is N/A
1.00g
128.17g/mol
x
1000𝑚𝑚𝑜𝑙
1𝑚𝑜𝑙
= 7.81 mmol
Name:
Exp # 1
Date:
Lab Partner
In a preparative experiment, calculate the limiting reagent and the theoretical yield of the product.
Be sure to include your calculations for these values. Lab 1 is not a preparative experiment.
5. Procedure, Observations and Data
Procedure (4 point)
Observations and Lab Data (4 point)
Name:
Lab Partner
Exp # 1
Date:
A summary of the procedure done with bullet points)
(2 points)
Part I: Solubility Tests
•
•
•
•
•
•
•
•
•
Add about 0.02 g of naphthalene each into
five test tubes (Number the test tube 1 to 5)
Add 0.5 mL of water into test tube 1
Add 0.5 mL of ethanol into test tube 2
Add 0.5 mL of acetone into test tube 3
Add 0.5 mL of hexane into test tube 4
Add 0.5 mL of toluene into test tube 5
Swirl the test tubes and wait a couple of
minutes and make note if the compound is
dissolved.
If compound is not dissolved at room
temperature, clamp the test tube and heat the
mixture to boil in a water bath and make note
if the compound is dissolved at boiling
temperature.
Choose the proper solvent for
recrystallization based on your result.
.
Part II: Recrystallization of Naphthalene
•
•
•
Transfer 0.97-1.03 g of impure naphthalene
to a 50-mL Erlenmeyer flask equipped with a
stir bar.
Heat the solvent (determined in Part I, 10 ml)
on a hot plate to a gentle boil and add the hot
solvent in small amount to the flask and
swirling and heating between each addition
until the sample just dissolved.
If the solution is colored, decolorize the
solution by carrying out the following steps:
• Move the flask away from the hot plate to
allow it to cool slightly (10 to 20 degree
below boiling point) then add a
microspatula-tip full of carbon (Do not
add the carbon to a boiling solution!)
• Reheat the mixture to boiling for 2
minutes.
• Move the flask away from the hot plate to
allow it to cool slightly then add a 0.2 g of
Report all observations and all data that you collect in the
lab here
(What is the characteristic of naphthalene?)
(What are the colors of each solvent?)
(Which solvents dissolve naphthalene at room
temperature?)
(Which solvents dissolve naphthalene at elevated
temperature?)
(Which solvent you pick as proper solvent for
recrystallization?)
(What is the characteristic of naphthalene and how
much of it do you weigh? Report all digits you
observe on the balance)
How much solvent do you add in total?
What is the color of the solution?
What do you observe when adding activated carbon?
Name:
Lab Partner
•
•
•
•
Exp # 1
Date:
filter aid (Celite) (Do not add directly to a
boiling solution!)
• Reheat the mixture to boiling for 2
minutes.
• Perform a hot gravity filtration using the
other 50 mL Erlenmeyer flask to receive
the filtrate.
If the solution is not colored, add additional
0.5 mL of solvent to the mixture, record the
total amount of ethanol added, then remove
any insoluble impurities by gravity filtration.
• Wet the flute filter paper with the hot
solvent and filter the solution.
• Rinse the flask with small amount of hot
solvent and filter each rinse.
• Rinse the filter paper with small amount
of hot solvent to minimize product loss.
Cover the flask with filtrate with a watch
glass and allow the solution to cool to room
temp so that crystals form slowly. When no
more crystals form, place the flask in an icewater bath for 15 min.
• Collect the crystals on Buchner funnel by
vacuum filtration
• Wet the filter paper with cold solvent and
filter the crystals
• Rinse the flask with small amount of cold
solvent to transfer all crystals onto the
Buchner funnel.
• Wash the filter cake with 1 mL of cold
solvent twice.
Allow the crystals dry under vacuum for
additional 5 minutes.
Determine the yield and obtain a melting
point.
Any observation on hot gravity filtration?
Any crystal formation? Shape and color?
What is the characteristic of your pure crystal?
Report the mass of pure naphthalene
Report the melting point naphthalene
Name:
Lab Partner
Exp # 1
Date:
6. Conclusions and discussions (4 points)
•
Briefly explain your experiment, how it worked, the result you got and what those
results mean.
•
When discussing a product, be sure to address issues such as product identification
(appearance, b.p., m.p., etc), purity, actual yield, and percent of recovery.
•
Compare the melting point of your purified naphthalene to that in the literature and
what conclusion do you draw here?
•
Percent yield is succinctly rationalized. Unknown identification is rationalized, if
applicable.
•
If your results are inconclusive or inconsistent, mention that here and suggest possible
sources of error.
7. Post-lab questions
I. The goal of the recrystallization procedure is to obtain purified material with a
maximized recovery. For each of the items listed, explain why this goal would be
adversely affected.
1. In the solution step, an unnecessarily large volume of solvent is used.
2. The crystals obtained after filtration are not washed with fresh cold solvent
before drying.
3. The crystals referred to in (2) are washed with fresh hot solvent.
4. A large quantity of decolorizing carbon is used.
5. Crystals are obtained by breaking up the solidified mass of an oil that originally
separated from the hot solution.
6. Crystallization is accelerated by immediately placing the flask of hot solution in
an ice-water bath.
II. In the course of a synthesis of an important antibiotic, an impure solid was
obtained as one of the intermediates. The solubility of this material in various
solvents is shown below.
Name:
Exp # 1
Date:
Lab Partner
Water
Ethanol Toluene Petroleum 2Acetic
Ether
Butanone Acid
Cold
Insoluble Soluble
Insoluble Insoluble
Soluble
Slightly
soluble
Hot
Slightly
soluble
Soluble
Soluble
Soluble
Soluble
Insoluble
Which of the solvents above would be the most suitable for recrystallization of the
impure solid? Explain your reasoning.
8. References:
1. Gilbert, J. C.; Martin, S. E. Experimental Organic Chemistry: A Miniscale and
Microscale Approach, 6th ed.; Cengage Learning, 2016; pp91-101.
2. Gao, X. G. Experiment 1: Purification of Solids by Recrystallization
, 2020. Blackboard, Caldwell University, NJ
https://caldwell.blackboard.com/webapps/blackboard/content/listContentEditabl
e.jsp?content_id=_541880_1&course_id=_13551_1&content_id=_542444_1
(accessed Aug 22, 2020).
9. Image of your lab notebook. (3 point)
Please attach a picture or pdf file of your lab note (the print-out pre-lab write-up with
recorded data and observations) at the end of report.
I reserve the right to modify points on this template at any time.