What factors must be considered when choosing a solvent for an extraction consis
ID: 946296 • Letter: W
Question
What factors must be considered when choosing a solvent for an extraction consisting of an aqueous phase and an organic phase? Identify the physical property that determines if the organic compound will be found in the organic or aqueous layer and the physical property that will determine which will be the top and bottom layers. Note that, in practice, we perform what is called a "water drop test" to check which layer is organic and which layer is aqueous. Explain how adding water during an extraction will help you determine which layer is organic and which is aqueous. Pavia uses the term "extraction"Explanation / Answer
1 ) a.A distribution coefficient other than unity implies that the solute must have different affinity in the two phases.
b.he solvent should have low solubility in the feed solution, otherwise the separation is not "clean".
c.It is always necessary to recover the solvent for re-use, and this must ordinarily be done by other means, eg. distillation.
d.The solvent should be stable chemically and inert toward the other components of the system and toward the common materials of construction.
e.These should be low for ease in handling and storage, for example, a high viscosity leads to difficulties with pumping , dispersion and mass-transfer rate.
f.An excellent solvent may not be commercially available.
After seperation there are two layers are formed.Below layer is water layer & upper one is organic layer.
2 ) If you drip a drop of water into the test tube having two layers, one of two things will happen. Either:
1) The drop will immediately dissolve as soon as it hits the top layer of liquid. In that case, the top layer is your aqueous layer!
-or-
2) The drop will not dissolve when it hits the top layer of your test tube, but instead will probably sink as a droplet down through the top layer. When that drop reaches the lower layer, it should dissolve. That is because the top layer is the organic layer, and the lower layer is aqueous.
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