Atlanta Technical College McClures Eight Step Research Process Paper No PlagiarismRead this week’s assigned article, “Googlepedia: Turning Information Beha

Atlanta Technical College McClures Eight Step Research Process Paper No PlagiarismRead this week’s assigned article, “Googlepedia: Turning Information Behaviors into Research Skills” (Links to an external site.) by Randall McClure. Next, respond to the questions below in a thoughtful, original post. Finally, respond to at least one classmate’s thoughts on McClure’s research process.Share your thoughts on McClure’s eight-step research process. What is the most valuable part of the process? Which parts seem tedious or confusing? Compare this process to your previous research method(s). How can this process help you search more effectively, overall? EXP 3-1
RECRYSTALLIZATION (MICROSCALE)
UNLV CHEM 241L SUMMER 2020
RECRYSTALLIZATION:
Introduction
• Read INTRODUCTION and THEORY OF CRYSTALLIZATION sections in the provided lab
manual.
• Understand the basic concept of recrystallization
• Review the polarity concept from the previous lab (solubility and solution) if necessary
RECRYSTALLIZATION :
Introduction
• Recrystallization
? a purification technique for solid compounds
? the solubility of a compound in a specific
solvent is the most important property
• Good recrystallization solvent?
? sparingly soluble at room temperature
? highly soluble at elevated temperature (boiling
temperature)
RECRYSTALLIZATION :
Experimental
• Purification of impure naphthalene by two recrystallization solvents
? ethanol
? hexane
• Determine which solvent is a good recrystallization solvent for naphthalene
? based on experimental melting point provided in the video
? based on the % recovery of naphthalene from each recrystallization
Experiment # 3-1:
Recrystallization (Micro-scale)
INTRODUCTION
In most organic chemistry experiments, the desired product is first isolated in an impure form. If
this product is a solid, the most common method of purification is crystallization. The general
technique involves dissolving the material to be crystallized in a hot solvent (or solvent mixture)
and cooling the solution slowly. The dissolved material has a decreased solubility at lower
temperatures and will separate from the solution as it is cooled. This phenomenon is called
crystallization, if the crystal growth is relatively slow and selective, or precipitation, if the
process is rapid and nonselective. Crystallization is an equilibrium process and produces very
pure material. A small seed crystal is formed initially, and it then grows layer by layer in a
reversible manner. In a sense, the crystal “selects” the correct molecules from the solution. In
precipitation, the crystal lattice is formed so rapidly that impurities are trapped within the lattice.
Therefore, any attempt at purification with too rapid a process should be avoided. Because the
impurities are usually present in much smaller amounts than the compound being crystallized,
most of the impurities will remain in the solvent even when it is cooled. The purified substance
can then be separated from the solvent and from the impurities by filtration.
THOERY OF CRYSTALLIZATION
The first problem in performing a crystallization is selecting a solvent in which the material to be
crystallized shows the desired solubility behavior. In an ideal case, the material should be
sparingly soluble at room temperature and yet quite soluble at the boiling point of the
solvent selected. The solubility curve should be steep, as can be seen in line A of Figure 1. A
Figure 1. Graph of solubility vs. temperature.
1
curve with a low slope (line B) would not cause significant crystallization when the temperature of
the solution was lowered. A solvent in which the material is very soluble at all temperatures (line
C) also not be suitable crystallization solvent. The basic problem in performing a crystallization is
to select a solvent (or mixed solvent) that provides a steep solubility-vs.-temperature curve for the
material to be crystallized. A solvent that allows the behavior shown in line A is an ideal
crystallization solvent.
A successful crystallization depends on a large difference between the solubility of a material in
a hot solvent and its solubility in the same solvent when it is cold. When the impurities in a
substance are equally soluble in both the hot and the cold solvent, en effective purification is not
easily achieved through crystallization. A material can be purified by crystallization when both the
desired substance and the impurity have similar solubilities, but only when the impurity represents
a small fraction of the total solid. The desired substance will crystallize on cooling, but the
impurities will not.
In this experiment, you will perform a micro-scale crystallization. Impure naphthalene will be
recrystallized from hexane and ethanol separately, and you will determine a good recrystallization
solvent for naphthalene based on melting point measurement and % recovery.
PROCEDURE (experiment video, https://youtu.be/cilrcJrcTXM)
1. Prepare a hot water bath using 50 or 100 mL beaker with half-full of water at the
beginning of the class.
2. Transfer 0.1 g of impure naphthalene to a Craig tube.
3. Add 1 mL of ethanol to the Craig tube and stir the Craig tube by tapping with your
finger. .
Note: Record the solubility of naphthalene in ethanol at room temperature.
4. Place the Craig tube in the hot water bath. The solution should be stirred continuously
with a spatula using a twirling motion until all solid has dissolved.
Note: Carefully pay attention to the solubility of naphthalene by doing this.
5. If necessary, additional portions of ethanol can be added until all solid has dissolved.
Figure 2. Assembling of the Teflon plug and the centrifuge tube.
2
6. Remove the Craig tube from the hot water bath and place it in a 25 mL Erlenmeyer
flask and cover the Craig tube with a small piece of aluminum foil. Allow the solution
cool slowly.
7. Obtain the Teflon plug and wrap it with about 8-inch piece of a metal wire around the
neck of the Teflon plug (your instructor will demonstrate this).
8. Assemble the Teflon plug and a centrifuge tube as shown in Figure 2.
9. Place the assembly in the centrifuge.
Note: Make sure the centrifuge is balanced.
10. Turn on the centrifuge for about 1 minute. Remove the assembly when spinning stops.
11. Lift the Craig tube out of the centrifuge tube by lifting the wire.
12. Gently remove the Teflon plug and collect all crystals onto a clean pre-weighed 10 mL
beaker.
13. Determine the recovery mass and % recovery.
14. Repeat the procedure using hexane.
15. Determine the melting point of recrystallized naphthalene and record in your notebook.
3
Notes for the Template:
1.
2.
Do not turn in this first page (which is this page you are looking
at now).
Remove all text inside of the parenthesis as well as the example
paragraphs. Your final write-up shouldn’t contain any parenthesis
except for the ones you choose to add. There will be point
deduction if you still have them in your final, submitted draft.
NAME: (your name)
CHEM 241L
SECTION #: (your section #)
UNLV 2020 Summer Session II
RECRYSTALLIZATION
PURPOSE
(Specifically state the purpose of the experiment and evaluation methods in a few
sentences.)
Example:
The purpose of this experiment is to separate hexane and toluene from a mixture by distillation using
Hickman Still apparatus. After isolation of each component, gas chromatography is used to evaluate the
efficiency of the Hickman distillation technique performed.
PROCEDURE
(Write a paragraph of the detailed experimental procedure including observation in 3rd
person past tense from the experiment video. In this report, do not copy and paste the
lab manual procedure. See the following example for your understanding.)
Example:
316 mg of ferrocene (1.7 mmol) and 2 mL of acetic anhydride were placed in a 10 mL of round-bottom flask,
to this mixture, 10 drops of 85% phosphoric acid was added slowly with stirring. A water-cooling condenser
was attached, and the mixture was heated for 20 minutes in a 90 ?C water bath. After cooling down, 1.0 mL
of ice-cold water was added dropwise to the reaction mixture. The diluted mixture was poured into a 50 mL
beaker containing about 10 g of ice. The mixture was neutralized by adding approximately 5 g of solid
sodium bicarbonate (about 0.25 g at a time) until the CO2 stops bubbling off and pH = 5 – 6 with the pH
paper testing. The crude solid product was collected by vacuum filtration and washed thoroughly with cold
water. After determining the mobile phase by TLC, the crude product was purified by column
chromatography using ethyl acetate/hexane (1:9, v/v).
DATA/RESULTS
(Record all collected and calculated data from the experiment video. Fill all necessary
values in the table.)
? RECRYSTALLIZATION OF NAPHTHALENE
Recrystallization
Solvent
Actual amount
used (mg)
Recovered
amount (mg)
% recovery
Ethanol
Hexane
CONCLUSION
(This is the section in which you interpret the data obtained in the previous section. It
demonstrates that you understand and can interpret the data you have collected. Interpret
the data obtained, observations, graphs, etc. and compare with literature sources where
necessary. Relate the experimental results to the theory discussed in the introduction.
This section also addresses the yield and purity of products and possible sources of error
that may have influenced these results.)
(For this experiment, include the following specifics)
– Summarize the results and compare each recrystallization solvent.
Post-Lab Questions
1. How would you assess the purity of recrystallized naphthalene at the end of this
experiment? Choose a method and explain how it tells us the purity of it for full
credit.
2. Why hexane didn’t work very well to recrystallize the impure naphthalene although
the same amount of solvent was used as the ethanol recrystallization. Explain.
3. How would you improve the hexane recrystallization to obtain a higher % recovery?

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