Methods of purification of organic compounds - class-XI

The reagent selected should be such that only one of components to be separated, reacts with it.

Using Dalton's law for steam distillation: P_total = P_water + P_chlorobenzene. 740.2 = 530 + P_chlorobenzene, so P_chlorobenzene = 210.2 torr. The mole ratio n_c/n_w = P_c/P_w = 210.2/530 = 0.396. Mole fraction of chlorobenzene = 0.396 / (1 + 0.396) = 0.283, or 28%.

Sublimation is used for benzoic acid and benzaldehyde (iii). Distillation is for ether and toluene (i). Vacuum distillation is for glycerol (iv). Steam distillation is for o-nitrophenol and p-nitrophenol (ii).

• Sublimation-Conversion of solid directly into gaseous phase. The liquid state does not exist. e.g., naphthalene, anthracene. 
• Beilstein test-Simple chemical test for halogens. 
• Victor-Meyers method-Standard laboratory method for determining the molecular weight of a volatile liquid. 
• Steam distillation- Vaporization of the volatile constituents of a liquid. It is special type of distillation for temperature-sensitive materials like aromatic natural compounds, eg,-ortho nitrophenol, cinnamaldehyde. 
• Vacuum distillation-Distillation at reduced pressure. It is generally used in case of high boiling liquids which decompose below their normal boiling points, cant be purified by distillation at atmospheric pressure.

Sublimation is the process in which solid changes directly to vapour state without passing through the liquid state.So sublimation cannot be used for purification of liquids.

The purity of an organic compound can be tested by its sharp melting point. The impurities present in the compound can cause a decrease in melting point.

An azeotropic is a mixture of 2 or more liquids in such a way that its components cannot be altered by simple distillation, This happens because when an azeotrope is barred, the vapour has the same proportions of constituents as the unboiled mixture.
Azeotropes are also called constant boiling mixture,
Rectified spirit is an azeotropic mixture of ethanol and water. 

d- tartaric acid and l - tartaric acid can be
separated by Salt formation.
Two enantiomers of sodium ammonium salt of tartaric acid give rise to two distinctly different types of chiral crystals that can be easily separated.

Generally speaking you need to take polar solvents for polar compound and nonpolar solvents for nonpolar compounds. Many times a mixture of solvents works better. Once you have this basic idea, crystallization is a skill developed over a period of time by trial and error process. Even after long experience you may not hit the right solvent in the first try.

The fractional column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.

Sublimation is the process in which solid gets converted into vapours directly without passing through the liquid state.

All the listed statements are correct: simple distillation is for stable liquids, reduced pressure for heat-sensitive liquids, and steam distillation for immiscible liquids.

Sublimation will separate C from A and B. On adding water, A will dissolve but B will not. B can be separated by filtration. A will be present in the filtrate and can be obtained by crystallisation from water extract.

Distillation is the process of purifying water by removing contaminants.

The steam distillation process works on the principle that when a mixture of two or more undissolved liquids are heated, while ensuring that the surfaces of both liquids are in contact with the atmosphere, the vapor pressure exerted by the system increases. This method is used for the refining of petroleum. 

Fractional distillation is for liquids with similar boiling points (d). Fractional crystallization is for solids with different solubilities (b). Vacuum crystallization is for substances that decompose at their boiling point (c). Solvent extraction is for liquids with different solubilities (a).