Methods of purification - 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 silt in $H _2O$ remains suspended. To attract some more silt particles, $Al(OH) _3$ is used. It is used to absorb the silt particles and make the liquid more pure.

Electrolysis is the only physico-chemical method. Rest all are physical processes.

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).

Steam distillation is used to separate essentials oils so that the temperature goes nowhere near their boiling points,
which minimises the risk of decomposition.
Steam distillation is used and not simple distillation for separating essential oils.

A mixture of two gases can be separated by fractional distillation technique. Fractional distillation is a process by which components in a chemical mixture are separated into different parts called fractions according to their different boiling points.

Simple distillation is used to separate volatile liquids from non-volatile impurities having sufficient difference in their in their boiling points.
A mixture of ether (B.P $35^{0}$) and toluene (B.P $110^{0}$) since they have large boiling point difference.

Vacuum distillation is a method of distillation whereby the pressure above the liquid mixture to be distilled is reduced to less than its vapour pressure causing evaporation of the most volatile liquids.

The distillation of tar do not give Phenol & naphthalene, or Benzol & pitch or Anthracene & creosote.

Styrene is heat-sensitive and tends to polymerize at its normal boiling point. Therefore, it must be purified by vacuum distillation to lower its boiling point.

Vacuum distillation is used when the boiling point of the compound or the solvent is too high in order to distill the compound or the solvent off without significant decomposition. It is based on the fact that under vacuum the boiling point of the materials is lower than at normal atmospheric pressure. Glycerine, glycerol and propone 1,2,3-triol are the three names of the same compound. It has a boiling point of 290$^oC$ while ethanol has BP 79$^oC$ .

Option A, B and C are correct.

o-Nitrophenol exhibits intramolecular hydrogen bonding, making it more volatile than p-nitrophenol, which exhibits intermolecular hydrogen bonding. Steam distillation exploits this difference in volatility.

102 g H2O2 is 3 moles. The reaction produces 1 mole H2O2 per mole of (NH4)2S2O8. Electrolysis requires 2 moles of electrons per mole of persulfate. Total electrons = 6 moles. Faraday = 96500 C. Q = 6 * 96500 = 579,000 C. Current = Q/t = 579,000 / 3600 = 160.83 A. With 50% efficiency, I = 160.83 / 0.5 = 321.67 A.

Osazones are characteristic crystalline derivatives formed by the reaction of reducing sugars (carbohydrates) with phenylhydrazine. They are used to identify specific sugars.

Steam distillation of a liquid in a current of steam used especially to purify liquids that are not very volatile and are immiscible with water. The boiling point of turpentine oil is between 90 and 115 °C or 195 and 240 °F and is immiscible with water. Thus, it is purified by steam distillation.

Aqueous solution of $NaHCO _3$ can be used to separate benzoic acid from its mixture with camphor. Benzoic acid forms water soluble sodium benzoate with $NaHCO _3$. So, A mixture of camphor and benzoic acid can be easily separated by Chemical method.

Option C is correct.

Due to the difference between the boiling point of components, distillation can be used for separation.

In steam distillation, the mixture boils when the sum of vapour pressures of water and the organic liquid becomes equal to the atmospheric pressure. Since the vapour pressure of water is appreciably higher than that of the organic liquid, it vaporizes at a temperature much lower than its normal boiling point. 

 (3) Distillation of coal tar : Arenes are isolated by fractional distillation of coal tar,

Table : 

Name of the fraction

	Temperature range (K)

Main constituents

Light oil (or crude oil) fraction
Middle oil fraction (Carbolic oil)
Heavy oil fraction (Creosote oil)
Green oil (Anthracene oil)
Pitch (left as residue)

 So at 443-503 K temperature phenol and naphthalene is formed

Hence options A & C are correct.

Distillation procedures will give us water free from all impurities. The distillation process removes almost all impurities from water. Distillers are commonly used for removing nitrate, bacteria, sodium, hardness (dissolved solids), most organic compounds, heavy metals and radionuclides from water. Distillers remove about 99.5% of the impurities from the original water.

As the component is miscible with water vapour in vapour phase so steam distillation will be most suitable method for extraction.

Distillation under reduced pressure lowers the boiling point of a liquid, which prevents the thermal decomposition of substances that are heat-sensitive. This technique is essential for liquids with high boiling points that would otherwise break down before reaching their boiling point at atmospheric pressure.