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Final

CHM 1321 Study Guide - Final Guide: Separatory Funnel, Methylene Blue, Crystal Violet


Department
Chemistry
Course Code
CHM 1321
Professor
William Ogilvie
Study Guide
Final

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Introduction
Extraction is a technique used when separating different chemical compounds in a
mixture by using the concept of solubility differences of two immiscible solvents: an
aqueous and organic phase. It involves extracting one compound from one phase to the
other in order to eliminate any impurities. Extraction is carried out most efficient when
using a piece of glassware called separatory funnel. The funnel is tapered, has an opening
at the top and a stopcock at the bottom. The solution would then be poured into the
separatory funnel and shaken with a solvent. The stopcock at the bottom is used to
remove each phase separately.
The ratio of the solubility of the compound is called the distribution coefficient,
KD. A single extraction can only efficiently transfer a compound from one solvent to
another when KD’s value is large. Hence, repeating the extraction with small volumes of
the same solvent multiple times would increase the efficiency. It is important to be able to
identify the difference between an organic or aqueous phase. The organic layer is usually
less dense; therefore, it will be the top layer, while the bottom layer is aqueous. To
determine which layer is which is organic or aqueous, the addition of few drops of water
would do the job. The water droplets would dissolve almost immediately if the top later is
aqueous, or it would sink if the top layer is organic. If an extraction is inefficient, the
procedure of "salting out" can improve it by adding salt to the aqueous phase.
The reaction between an organic acid and a base will eventually produce an ionic
salt that is water soluble, while the reaction between an organic base and an acid will
produce a charged species that is more water soluble in the aqueous phase. The neutral
organic compound would remain in the organic base, while charged materials will be
more soluble in water. Using acid-base chemistry, the formation of charge can be
reversed. To regenerate neutral organic forms, charged organic materials can be
recovered through the addition of acid or base.

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Observations
Part A – Extraction of Water Soluble Dye
Appearance of layer after adding
methylene blue
- Dark, opaque blue organic matter at the
bottom
- Slightly light, transparent blue aqueous
solution on top
Appearance of layer after adding methyl
red
- Clear, transparent organic matter at the
bottom
- Dark, transparent red aqueous solution
on top.
Appearance of layers upon mixing
methylene blue and methyl red
- Methyl red solution rises to the top
- Methylene blue solution sinks to the
bottom
We note that methylene blue is polar, while methyl red if non-polar. Therefore, an
extraction with ether as the organic phase and water as the aqueous phase would be a
good way to separate a mixture of these two compounds.
Salting Out Effect
Appearance of tube without NaCl
- Clear, transparent liquid
Appearance of tube with NaCl
- Cloudy, light purple on top
- Thick, translucent purple at the bottom
Adding NaCl to a test tub containing water, 1-butanol and crystal violet decreased the
amount of dye in the aqueous level. This is because the NaCl dissociated to form Na+ and
Cl- ions that are attracted more strongly to the polar dipoles of the water molecules than
the crystal blue. This tied up more of the dipoles of the water molecules, decreasing the
number of bonds that could be made to the crystal violet dye, and so it concentration in
the aqueous layer decreased.
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