What is the purpose of recrystallization? What is the purpose of vacuum filtrati

Question

What is the purpose of recrystallization? What is the purpose of vacuum filtration during the crystallization procedure? What is the purpose of using thick walled rather than thin walled tubing for a vacuum filtration? How does one take a mixed melting point, and how does a mixed , melting point help identify a compound? What Is the purpose of distillation? What is the purpose of using a column filled with beads in a distillation? Chloroform has a density of 1.48 g/ral, and is not soluble in water. In a breaker containing water and chloroform, Which layer wound be on top? About the extraction the labs: What was the purpose of adding Na_2SO_4 to the other layer?

Explanation / Answer

Ans 4-a)

The purpose of recrystallization is to purify compound by removing impurities. It involves dissolving mixture of compound containing impurities in suitable solvent followed by crystallization of either compound or impurity by changing conditions such as temperature or proportion of solvent.

Ans 4-b)

During crystallization, once compound is crystallized it has to be separated from mother liquor (remaining solution). This can be achieved by using filtration. However, filtration can be at times very slow, which may affect purity of crystallized compound. Thus, speed of crystallization is improved by using vacuum filtration.

Ans 4-c)

During vacuum filtration a thin walled tube may not be able to sustain vacuum applied and will collapse inward due to vacuum. Thus, vacuum may not get applied to filtration flask or very little vacuum will get applied. Therefore, thick walled tubing is used for vacuum filtration.

Ans 4-d)

Mixed melting point is taken by mixing together equal portions of two sample followed by detection of melting point of this mixture. It is useful when two compounds have same melting point. If the melting point of mixture is same, then two compounds are identical. If the melting point of mixture is low then two compounds are not identical. Two different compounds having same melting point reduces the melting point of their mixture.

Ans 4-e)

Distillation is a purification technique. It can be used to separate components of liquid mixture by selective evaporation and condensation depending upon difference in the boiling points of the components.

Ans 4-f)

If the components of liquid mixture have boiling points very close to each other, then use of column with beads can help in separation of these components in distillation. The technique is also called as fractional distillation.

Ans 5)

Density of chloroform is 1.48 g/mL and that of water is 1.0g/mL. Thus, chloroform is heavier than water.

Therefore, in a beaker containing water and chloroform, layer of chloroform will the at the base due to its heavy nature and layer of water will be on top.

Ans 6-a)

Na2SO4 acts as desiccant and it removes small amount of water present in ether layer obtained after extraction from aqueous layer.

Ans 6-b)

‘Decant the liquid from Na2SO4 means’, separation of dry ether layer from wet Na2SO4 by simply pouring it out as the wet Na2SO4 will settle at the bottom

Ans 6-c)

The purpose of putting round bottom flask with compound in it into a vacuum desiccator is to completely dry it by removing small amount of moisture present in it.

Ans 6-d)

[Note: molecular formulas are not clearly visible]

5% NaOH can convert carboxylic acid into its water soluble sodium salt. Thus, Carboxylic acid will remain in aqueous solution and other components (provided they are not water soluble) will be in ether layer.

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