Experiment #6: Separation and Identification of
an Unknown Binary Mixture
Objective:
To successfully separate and correctly identify the components of an unknown binary
mixture using various Organic Chemistry labora
...
Experiment #6: Separation and Identification of
an Unknown Binary Mixture
Objective:
To successfully separate and correctly identify the components of an unknown binary
mixture using various Organic Chemistry laboratory techniques.
Introduction:
Identity of unknown compounds is extremely vital for chemists. To ensure that they
identify these unknown compounds there are several tests that can be performed. In this
experiment a variety of organic chemistry methods were utilized to separate and purify an
unknown binary mixture, and determine the compounds of the mixture. First the solid-liquid
mixture under goes a basic vacuum filtration, and then each unknown is purified. Afterwards, an
IR spectroscopy is performed for each unknown. Solubility tests and classification tests are
performed for each to help determine what functional groups are present. Then, once the NMR
data is obtained, one can begin to conclude the identity of obtained compounds, and set up a
synthesis outline for derivatives.
There are two different techniques are used to purify our unknown: recrystallization was
performed for solid compound, simple distillation was performed for liquid part.
The technique of crystallization is one of the most valuable available for the purification
of solids. The basic idea of purification is easily understood and the manipulations are
straightforward. In spite of this, crystallization remains more of an art than a science. A part of
the trouble arises because a good crystallization frequently requires much patience. A more
serious problem is that the best solvent to use cannot be chosen by a convenient magic rule, but
must be found by trial and error.
The most fundamental property of a good solvent for crystallization of a solid is that the
hot solvent must dissolve the substance readily while the cold solvent must dissolve it sparingly.
This means that we would start our hunt for a good solvent by looking for one that gave
borderline solubility. From here we would have to adjust the temperature range, the ratio of solid
to solvent, or try combinations of solvents to find a mixture with just the right solvent properties.
In crystallization of a mixture of solids one is always faced with the practical problem of
knowing how much solvent to use. If one of the components is poorly soluble in the chosen
solvent one could go on adding the hot solvent for a long time before the mixture is dissolved
completely.
Distillation can be used as a method for purifying a single liquid and also as a means of
separating a liquid from a dissolved solid or from a mixture of miscible liquids. The liquid (or
mixture) is heated and when it boils, the vapors are condensed into a separate receiver. The
resultant liquid (distillate) is collected in one or more fractions.
A single liquid will begin to boil when its vapor pressure is equal to the vapor pressure of
the atmosphere. For a pure liquid the boiling temperature should remain constant (within 2°C)
for the duration of the distillation.
Once the two unknowns are purified, the solubility tests, classification tests, IR and
NMR can be performed to identify the compounds. Lastly, a derivative is formed for each
unknown to verify that the correct identity is determined. A derivative is basically a new
compound that formed from the unknown; however the main difference is that the derivative
usually has a new functional group. After forming the derivative, the functional group test is
performed and should be positive, whereas on the original unknown, it was negative. Also, the
MP and if it is similar to the literature melting point of the derivative, then this would prove that
a derivative was successfully created and the unknown was correctly identified.
Methods/Procedure:
Part A – Preliminary Examination
Part B – Vacuum Filtration
Part C – Recrystallization with melting point
Part D – Simple Distillation
Part E – Solubility Test (Experiment 55A, p. 45
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