Purification of Organic Compounds Questions in English

(B) The boiling points of methanol and acetone are $338 \, K$ and $330 \, K$ respectively.
Since their boiling points are very close to each other,they are separated by the fractional distillation method.

(B) Chromatography is a technique used for the separation of components of a mixture. It is based on the principle of differential distribution of the components of a mixture between two phases: a stationary phase and a mobile phase. This is known as phase distribution.

(D) Chromatography is a versatile technique used for the purification of organic compounds regardless of their physical state (solid,liquid,or gas).
For solid or liquid organic compounds,column chromatography is commonly employed by dissolving the substance in an appropriate solvent.
For gaseous compounds,gas chromatography is used.
Therefore,chromatography is applicable to all these states.

(B) Chromatography is the latest technique for the purification of organic compounds. Chromatography is of various types,such as column chromatography,gas chromatography,paper chromatography,etc.

(D) $o-$nitrophenol exhibits intra-molecular hydrogen bonding,whereas $p-$nitrophenol exhibits inter-molecular hydrogen bonding,which is significantly stronger.
Due to this difference in hydrogen bonding,the boiling point of $o-$nitrophenol is much lower than that of $p-$nitrophenol.
Consequently,$o-$nitrophenol is steam volatile and can be separated from $p-$nitrophenol using steam distillation.

(A) Fractional distillation is used because the difference between the boiling points of the different components in crude oil is relatively small,allowing them to be separated based on their volatility.

(C) Steam distillation,also known as vapour distillation,is a technique used for separating substances that are immiscible with water,volatile in steam,and possess high vapour pressure at the boiling temperature of water.
It is also used for purifying liquids that decompose at their normal boiling points.
Since ethylene has a high $b.p.$ and high vapour pressure at $100\,^{\circ}C$ and does not dissolve in water,it is separated by the vapour distillation method.

(C) Liquids that decompose at their boiling point can be purified by vacuum distillation.
Glycerol,which decomposes at its normal boiling point $(563\,K)$,can be distilled without decomposition at $453\,K$ under reduced pressure $(12\,mm\,Hg)$.

(A) Aniline is purified by steam distillation.
The temperature required for the simple distillation of aniline is too high,which causes it to decompose.
Steam distillation allows the process to occur at a lower temperature,preventing decomposition.

(A) In chromatography,the term $R_f$ stands for the $Retention \ factor$.
It is defined as the ratio of the distance traveled by the solute to the distance traveled by the solvent front from the baseline.
Mathematically,$R_f = \frac{\text{distance traveled by the solute}}{\text{distance traveled by the solvent front}}$.

(C) Crystallization is a technique used to purify solid organic compounds. The basic principle is that the compound to be purified should be sparingly soluble in a suitable solvent at room temperature but should dissolve readily in the same solvent at higher temperatures (near its boiling point). Upon cooling the hot saturated solution,the pure compound crystallizes out,leaving the impurities in the solution. Therefore,both properties mentioned in $A$ and $B$ are essential for an ideal solvent.

(A) Naphthalene is an organic compound that undergoes sublimation,which is the process of direct transition from solid to gas phase upon heating. Therefore,it is purified by the method of $Sublimation$.

(D) Chromatography is a versatile technique used for the separation and purification of mixtures. It can be applied to substances in various physical states,including $solids$,$liquids$,and $gases$. Therefore,all the given options are correct.

(B) Distillation is the process used to separate a volatile liquid from non-volatile impurities. In this method,the liquid is heated to its boiling point to form vapor,which is then condensed back into a liquid,leaving the non-volatile impurities behind in the distillation flask.

(B) Distillation is the process used to separate a mixture of liquids that have a sufficient difference in their boiling points.
In this process,the liquid with the lower boiling point vaporizes first,is condensed,and then collected,while the liquid with the higher boiling point remains in the distillation flask.

(C) In the soap industry,glycerol is obtained as a byproduct.
It is separated from the spent lye by the process of distillation under reduced pressure.
This is because glycerol has a high boiling point and tends to decompose at its normal boiling point.
By reducing the pressure,the boiling point is lowered,allowing it to be distilled without decomposition.

(A) Aniline is steam volatile and insoluble in water. Therefore,a mixture of aniline and water is separated by the process of $Steam \ distillation$.

(C) The purification of organic compounds is achieved through various techniques such as sublimation,crystallization,distillation,differential extraction,and chromatography.
Among the given options,$Distillation$ is a standard method used for the purification of liquids,especially those that boil without decomposition and have sufficient difference in their boiling points.

(D) Essential oils are steam-volatile and are immiscible with water.
They can be extracted from flowers using $Steam \ distillation$.
In this process,steam is passed through the plant material,which carries the volatile essential oils with it,and the mixture is then condensed and separated.

(B) The process of separating an organic compound from an aqueous solution is known as $Solvent \ extraction$.
In this method,the organic compound is more soluble in an organic solvent (like ether or chloroform) than in water.
When the organic solvent is added to the aqueous solution in a separating funnel,the organic compound gets transferred to the organic layer,which can then be separated.

(C) Camphor is a sublime substance,meaning it changes directly from a solid to a gas upon heating. Salt $(NaCl)$ does not sublime. Therefore,sublimation is the most suitable method to separate camphor from salt impurities.

(D) Chromatography is a versatile technique used in chemistry for multiple purposes.
It is primarily used for the $1.$ separation of components in a mixture,$2.$ purification of chemical compounds,and $3.$ testing the purity of compounds.
Therefore,all the given options are correct.

(B) The purification method based on the difference in solubilities of the compound and its impurities in a suitable solvent is known as $Crystallization$. In this process,the impure solid is dissolved in a minimum amount of a suitable solvent at a high temperature and then cooled slowly to obtain pure crystals of the compound.

(A) Distillation under reduced pressure is used for liquids that have high boiling points and tend to decompose at or below their boiling points at atmospheric pressure. By reducing the pressure,the boiling point of the liquid is lowered,allowing it to boil and vaporize at a temperature below its decomposition point.

(D) Steam distillation is used for the separation of aniline from a mixture.
Aniline is insoluble in water,but it is steam volatile.

(C) $o$-Nitrophenol and $p$-nitrophenol can be separated by steam distillation.
$o$-Nitrophenol is steam volatile due to the presence of intramolecular hydrogen bonding,which reduces its intermolecular attraction.
In contrast,$p$-nitrophenol exhibits intermolecular hydrogen bonding,leading to the association of molecules,which makes it less volatile.
Therefore,$o$-nitrophenol distills over with steam,while $p$-nitrophenol remains in the distillation flask.

(B) Spent-lye and glycerol are separated by distillation under reduced pressure.
Under reduced pressure,the liquid boils at a lower temperature,preventing thermal decomposition.
For example,glycerol boils at $290^{\circ}C$ with decomposition at atmospheric pressure,but at reduced pressure,it boils at $180^{\circ}C$ without decomposition.

(A) Steam distillation is a separation process used to purify substances that are volatile in steam,immiscible with water,and possess a high boiling point.
The principle of steam distillation is that the mixture boils when the sum of the vapor pressures of the two immiscible liquids (water and the organic compound) equals the atmospheric pressure.
Since the vapor pressure of the mixture is higher than that of the individual components,the mixture boils at a temperature lower than the boiling point of either component.
Aniline is immiscible with water and has a high boiling point $(184 \ ^{\circ}C)$,making steam distillation the ideal method for its separation.

(A) Crude oil is a mixture of various hydrocarbons with different boiling points.
Fractional distillation is the process used to separate these components based on their differences in boiling points.
In the petroleum industry,this is carried out in a fractionating column where the crude oil is heated,and different fractions are collected at different heights corresponding to their boiling ranges.

(A) Steam distillation is a separation process used for substances that are volatile in steam and immiscible with water.
The principle of steam distillation is that the mixture boils when the sum of the vapor pressures of the two components (water and the organic substance) equals the atmospheric pressure.
Since the vapor pressure of the mixture is higher than the vapor pressure of the individual components,the mixture boils at a temperature lower than the boiling point of either component.
Aniline is immiscible with water and volatile in steam,making steam distillation the ideal method for its separation from water.

(D) $1$. Ortho-nitrophenol is steam volatile due to intramolecular hydrogen bonding,while para-nitrophenol is not due to intermolecular hydrogen bonding. Thus,they are separated by steam distillation. (Correct)
$2$. Fractional distillation is used when the difference in boiling points is small (less than $20\,^{\circ}C$ to $30\,^{\circ}C$). The statement mentioning $10\,^{\circ}C$ is generally acceptable in this context. (Correct)
$3$. Aniline is sensitive to high temperatures and decomposes before boiling at atmospheric pressure; therefore,it is purified by steam distillation. (Correct)
$4$. Glycerol is separated from spent lye in the soap industry by distillation under reduced pressure,not by fractional distillation. (Incorrect)

(C) The most commonly used adsorbents in column chromatography are $Al_2O_3$ (alumina) and silica gel $(SiO_2)$.
These materials are preferred because they possess a high surface area and are porous in nature,allowing them to adsorb substances onto their surface through intermolecular forces.

(A) Steam distillation is a technique used for the purification of organic compounds that are steam volatile and insoluble in water.
For a compound to be separated by this method,it must possess a high vapor pressure at the boiling point of water $(100 \ ^\circ C)$ and should not react with water.

(B) $1$. Naphthalene is a neutral organic compound,while tetrahydroisoquinoline is a basic amine.
$2$. When treated with $HCl$,the basic tetrahydroisoquinoline reacts to form a water-soluble salt (tetrahydroisoquinolinium chloride),which enters the aqueous layer.
$3$. Naphthalene remains in the diethyl ether layer. Evaporation of the ether layer yields $A =$ naphthalene.
$4$. The aqueous layer contains the salt of the amine. Adding $NaOH$ makes the solution basic,converting the salt back to the free base (tetrahydroisoquinoline),which is organic-soluble and moves into the ether layer.
$5$. Evaporation of this second ether layer yields $B =$ tetrahydroisoquinoline.
$6$. The remaining aqueous layer contains inorganic salts like $NaCl$ formed during the neutralization. Evaporation of this layer yields $C =$ inorganic ions such as $Na^{+}$ and $Cl^{-}$.

(A) . Coloured impurity is removed by charcoal treatment $(r)$.
$B$. Mixture of $o-$nitrophenol and $p-$nitrophenol is separated by steam distillation $(p)$ because $o-$nitrophenol is steam volatile due to intramolecular hydrogen bonding.
$C$. Crude naphtha is separated by fractional distillation $(q)$.
$D$. Mixture of glycerol and sugars is separated by distillation under reduced pressure $(s)$ to prevent decomposition of glycerol at high temperatures.
Therefore,the correct match is $A-r, B-p, C-q, D-s$.

(B) Partition chromatography is based on the continuous differential partitioning of components of a mixture between a stationary phase and a mobile phase.
In partition chromatography,the stationary phase is typically a liquid held on a solid support,whereas in adsorption chromatography,the stationary phase is a finely divided solid adsorbent.
Therefore,the statement that the stationary phase is a finely divided solid adsorbent is incorrect for partition chromatography.

(B) In chromatography,the substance being separated is the adsorbate,the stationary phase is the adsorbent,and the solvent is the mobile phase.
$a$. Benzaldehyde acts as the adsorbate $(r)$ which is adsorbed on the stationary phase.
$b$. Alumina $(Al_2O_3)$ is a common stationary phase used as an adsorbent $(q)$.
$c$. Acetonitrile is a common solvent used as a mobile phase $(p)$.
Therefore,the correct matching is $a \to r, b \to q, c \to p$.

(A) The density of dichloromethane $(DCM)$ is approximately $1.33 \ g/cm^3$,which is greater than the density of water $(H_2O)$,which is $1.00 \ g/cm^3$.
Because $DCM$ is denser than water,it will form the lower layer,and water will form the upper layer in a separating funnel $(S.F)$.

(B) Column chromatography is based on the principle of differential adsorption of substances on the solid stationary phase.
As the mixture moves through the column,different components are adsorbed to different extents,leading to their separation.
Therefore,option $B$ is correct.

(C) Liquids that decompose at or near their boiling point are purified by vacuum distillation.
Since glycerol decomposes at its normal boiling point of $563\,K$ $(290\,^oC)$,it is distilled under reduced pressure.
By lowering the pressure to $12\,mm\,Hg$,the boiling point of glycerol is reduced to $453\,K$,allowing it to be distilled without decomposition.

(B) Liquids that decompose at or below their boiling point are purified by vacuum distillation.
Glycerol decomposes at its normal boiling point of $563 \, K$.
By reducing the pressure to $12 \, mm \, Hg$,glycerol can be distilled at a lower temperature of $453 \, K$ without undergoing decomposition.

(D) Sublimation is a process used to purify substances that change directly from solid to gas phase upon heating.
Among the given halogens,$F_2$ is a gas,$Cl_2$ is a gas,and $Br_2$ is a liquid at room temperature.
$I_2$ (iodine) is a solid at room temperature and readily undergoes sublimation when heated.
Therefore,$I_2$ can be purified by the process of sublimation.

(B) In silica gel column chromatography,the stationary phase is polar (silica gel,$SiO_2$).
Compounds are separated based on their polarity; the least polar compound elutes first,and the most polar compound elutes last.
The polarity of the given compounds is determined by their dipole moments and hydrogen bonding capability:
$1.$ Acetophenone $(Ph-CO-CH_3)$: Dipole moment $\approx 3.05 \ D$.
$2.$ Benzanilide $(Ph-NH-CO-Ph)$: Dipole moment $\approx 2.71 \ D$ (has hydrogen bonding).
$3.$ Aniline $(Ph-NH_2)$: Dipole moment $\approx 1.59 \ D$ (has strong hydrogen bonding with silica gel).
However,considering the interaction with the polar stationary phase,the elution order depends on the strength of adsorption.
Aniline,being a primary amine,interacts strongly with the acidic silanol groups of silica gel.
Acetophenone is the least polar among the three.
Thus,the elution order is $(C)$ (Acetophenone) followed by $(A)$ (Benzanilide) and finally $(B)$ (Aniline).

(N/A) Crystallisation
Crystallisation is one of the most commonly used techniques for the purification of solid organic compounds.
Principle: It is based on the difference in the solubilities of the compound and the impurities in a given solvent. The impure compound is dissolved in a solvent in which it is sparingly soluble at room temperature but appreciably soluble at higher temperatures. The solution is concentrated to obtain a nearly saturated solution. On cooling the solution,the pure compound crystallises out and is removed by filtration.
Example: Pure aspirin is obtained by recrystallising crude aspirin. Approximately $2-4 \ g$ of crude aspirin is dissolved in about $20 \ mL$ of ethyl alcohol. The solution is heated to ensure complete dissolution. The solution is then left undisturbed until crystals start to separate out. The crystals are then filtered and dried.
$(b)$ Distillation
This method is used to separate volatile liquids from non-volatile impurities or a mixture of liquids that have a sufficient difference in their boiling points.
Principle: It is based on the fact that liquids having different boiling points vaporise at different temperatures. The vapours are then cooled and the liquids so formed are collected separately.
Example: $A$ mixture of chloroform $(b.p. = 334 \ K)$ and aniline $(b.p. = 457 \ K)$ can be separated by distillation. The mixture is heated in a round-bottom flask. Chloroform,being more volatile,vaporises first,passes into the condenser,and is collected as a liquid. Aniline remains in the flask.
$(c)$ Chromatography
It is one of the most useful methods for the separation and purification of organic compounds.
Principle: It is based on the difference in movement of individual components of a mixture through a stationary phase under the influence of a mobile phase.
Example: $A$ mixture of red and blue ink can be separated by chromatography. $A$ drop of the mixture is placed on the chromatogram. The component that is less adsorbed on the stationary phase moves faster with the mobile phase,while the more strongly adsorbed component moves slower.

(N/A) The differences among distillation,distillation under reduced pressure,and steam distillation are summarized in the table below.

Method	Description and Application
$1$. Distillation	Used for liquids that do not decompose on boiling and have sufficient difference in boiling points. Example: Separation of petrol and kerosene.
$2$. Distillation under reduced pressure	Used for liquids that decompose at their boiling point. Reduced pressure lowers the boiling point,preventing decomposition. Example: Purification of glycerol.
$3$. Steam distillation	Used for organic compounds that are steam volatile and immiscible in water. Example: Separation of aniline from water.

(N/A) Paper chromatography is a type of partition chromatography.
It involves the use of a special quality paper known as chromatography paper.
This paper contains water trapped in it,which acts as the stationary phase.
$A$ solution of the mixture is spotted on the base of this chromatography paper.
The paper strip is then suspended in a suitable solvent or a mixture of solvents,which acts as the mobile phase.
This solvent rises up the chromatography paper by capillary action and flows over the spot.
The components of the mixture are selectively retained on the paper based on their differing partition coefficients between the stationary phase (water) and the mobile phase.
As the mobile phase moves,the components travel to different heights on the paper.
The final paper strip obtained is known as a chromatogram.