Download The separation, purification and identification of the components of a

The separation, purification and identification of the components of a solid
organic mixture
Name:
Section #:
Unknown Letter:
Date:
I.
Experimental Data
A. Unknown Acid
Weight (dried) after extraction (g)
Weight (dried) after recrystallization
(g)
Solvent used for recrystallization (give
chemical name)
Melting point of the unknown acid
(°C)
Names of the references used in the
mixed melting point measurement
Reference #1:
Reference #2:
m.p. of the side-by-side determination
unknown:
mixture #1:
mixture #2:
literature value of the m.p. of the
reference #1 (°C)
literature value of the m.p. of the
reference #2 (°C)
Identity of your unknown acid (give
its chemical name)
B. Unknown Neutral
Weight (dried) after extraction (g)
Weight (dried) after recrystallization
(g)
Solvent used for recrystallization
(give chemical name)
Melting point of the unknown neutral
(°C)
Names of the references used in the
mixed melting point measurement
Reference #1:
Reference #2:
m.p. of the side-by-side determination
unknown:
mixture #1:
mixture #2:
literature value of the m.p. of the
reference #1 (°C)
literature value of the m.p. of the
reference #2 (°C)
Identity of your unknown neutral (give
its chemical name)
C.
Solubility test to determine an appropriate recrystallization solvent: (use “+” for soluble,
“-” for insoluble, and “” for partially soluble.
Water
cold
hot
Alcohol
Pet. ether
Acetone
Toluene
II.
Questions:
1. Explain why a mixture of an acidic and a neutral organic compound dissolved in ether can be
separated by extracting the mixture with an aqueous NaOH? (Hint: can the same mixture be
separated by extracting with water alone?)
2. Specify which of the following criteria should be met to be a good solvent for
recrystallization. Use (Y) for yes and (N) for no.
(A) The solvent should dissolve the solid when cold.
(B) The solvent does not react chemically with the solid.
(C) The boiling point of the solvent is above 100 °C.
(D) The boiling point of the solvent ideally is below the melting point of the solid to be
recrystallized.
3. Indicate which filtration technique, gravity (G) or vacuum (V) should be used for the
following process.
(A) Hot filtration to remove any insoluble impurity.
(B) Isolating recrystallized solid from the solution.
4. Fill in (T) for true or (F) for false for each of the following statement:
(A) An impurity raises the melting point of an organic compound.
(B) An eutectic mixture has a sharp melting point, just as does a pure compound.
(C) In a m.p. determination, the rate of heating should be extremely slow (1-2 °C per
minute) when the temperature is within 10-20°C of the expected m.p.
(D) A sample should be packed tightly into a capillary m.p. tube.
4. Why is it important to terminate the vacuum before turning off the water aspirator pump when
filtering your solid sample ?
5. When extracting an aqueous solution with an organic solvent, if you are unsure as to which
layer in the separatory funnel is aqueous, how could you settle the issue with a simple test
without looking up their density ?
6. If your recrystallized solid compound is not completely dry, what effect will this have on its
m.p. ?
7. During the process of recrystallization, why should the saturated solution be first cooled slowly
to room temperature then in an ice bath instead of being cooled to ice temperature immediately
?
8. In a Büchner funnel, can you use a filter paper that is too big and curls up around the edges?
Why?