Purification: Crystallization, Distillation & Sublimation — Practice Questions

Free NEET Chemistry multiple-choice questions on Purification: Crystallization, Distillation & Sublimation. Attempt each question and reveal the answer with a full explanation.

Which type of fractionating column consists of a glass tube with a series of glass 'indentations' or 'spikes' to increase surface area? Vigreux column Bubble plate column Packed column Liebig condenser Which type of fractionating column is commonly used in laboratories and consists of a glass tube with a series of indentations providing a large surface area for vapor condensation? Vigreux column Bubble plate column Liebig condenser Separatory funnel Which of the following mixtures can be most effectively separated using the process of sublimation? Ammonium chloride and Sodium chloride Ethanol and Water Benzene and Toluene Iron filings and Copper turnings The separation of a mixture of ortho-nitrophenol and para-nitrophenol is best carried out by which technique? Steam distillation Crystallization Sublimation Fractional distillation The choice of a solvent for the purification of an organic solid by crystallization depends on the criterion that: The compound is highly soluble at high temperature and sparingly soluble at low temperature The compound is equally soluble at all temperatures The impurities are completely insoluble in the solvent The solvent should have a boiling point higher than the melting point of the solid Fractional distillation is used for the separation of two liquids only when the difference in their boiling points is: Small (less than 25-30 K) Large (more than 100 K) Exactly 0 K Liquids are immiscible Steam distillation is based on the principle that many organic compounds are volatile in steam and are: Immiscible with water Miscible with water Soluble in hot water only More dense than water During the determination of the melting point of an organic compound, the presence of an impurity generally: Lowers the melting point and broadens the melting range Raises the melting point and narrows the melting range Has no effect on the melting point Increases the boiling point of the solid Which of the following techniques is most suitable for the purification of a liquid that tends to decompose at its normal boiling point? Distillation under reduced pressure Steam distillation Fractional distillation Simple distillation The method of 'Steam Distillation' is applicable to compounds which are: Steam volatile and insoluble in water Steam volatile and soluble in water Non-volatile and insoluble in water Non-volatile and soluble in water During crystallization, the solid is dissolved in a minimum amount of hot solvent. The purpose of cooling the solution slowly is to: Allow the formation of pure, large crystals Prevent the solvent from evaporating Increase the solubility of impurities Decrease the rate of precipitation Which of the following describes the correct order of increasing solubility of silver halides in ammonium hydroxide? AgI < AgBr < AgCl AgCl < AgBr < AgI AgBr < AgCl < AgI AgI < AgCl < AgBr Sublimation cannot be used for the purification of which of the following substances? Sodium chloride Camphor Iodine Naphthalene Which technique is most suitable for the separation of aniline from an aniline-water mixture? Steam distillation Fractional distillation Sublimation Crystallization Which of the following mixtures is best separated by the process of sublimation? Camphor and Magnesium chlorate Iodine and Sodium sulfate Benzoic acid and Sodium hydroxide Naphthalene and Anthracene A compound has a vapor density of 30 . Its empirical formula is CH 2O . What is its molecular formula? C 2H 4O 2 CH 2O C 3H 6O 3 C 4H 8O 4 Fractional crystallization is a technique used to separate two solids based on: The difference in their solubilities in the same solvent at different temperatures The difference in their boiling points The difference in their rates of sublimation The difference in their R f values The boiling point of a liquid is 150 C at 760 mm Hg. If the external pressure is reduced to 100 mm Hg, the boiling point of the liquid will: Decrease Increase Remain at 150 C First increase and then decrease A mixture of Benzene (b.p. 80 C ) and Toluene (b.p. 110 C ) is best separated by: Fractional distillation Simple distillation Steam distillation Sublimation Which of the following conditions must be satisfied for a liquid to be purified by steam distillation? The liquid must be steam volatile and immiscible with water. The liquid must be soluble in water and have a high boiling point. The liquid must be non-volatile and miscible with water. The liquid must be a solid at room temperature. The separation of two substances by fractional crystallization depends upon their difference in: Solubilities in the same solvent Boiling points Melting points Molecular weights What is the purpose of adding a small amount of silica gel or 'boiling chips' to the distillation flask? To prevent bumping of the liquid. To increase the boiling point. To act as a catalyst. To absorb moisture. What is the role of a 'fractionating column' in the distillation of two liquids with close boiling points? It provides multiple condensation and vaporization cycles in a single operation It increases the boiling point of the liquid with the lower vapor pressure It acts as a filter to trap solid impurities It reduces the atmospheric pressure within the distillation flask Which of the following organic compounds is expected to be most easily purified by the process of sublimation? Anthracene Urea Glucose Sucrose During the purification of an organic solid by crystallization, what is the 'mother liquor'? The solution remaining after the crystals have been filtered out The hot saturated solution prepared before cooling The solvent used for washing the crystals The impurity that remains insoluble in the hot solvent A mixture of iodine and common salt ( NaCl ) can be separated by which of the following methods? Sublimation Distillation Crystallization Filtration The purity of an organic compound is primarily determined by its: Melting point or Boiling point Molecular weight Physical state Color and Odor The separation of different fractions of petroleum (like gasoline, kerosene, diesel) is achieved using which process? Fractional distillation Steam distillation Vacuum distillation Simple distillation During the Dumas method, the nitrogen gas is collected over KOH solution. The pressure of the gas in the nitrometer is 760 mm Hg at 300 K. If the aqueous tension at 300 K is 25 mm Hg, the pressure of dry nitrogen gas is: 735 mm Hg 785 mm Hg 760 mm Hg 710 mm Hg The separation of a mixture of an organic compound and water by steam distillation is possible only if the organic compound is: Steam volatile and immiscible with water. Highly soluble in water. Non-volatile at 100 C . Solid at room temperature. During fractional distillation, the component with the lower boiling point will: Distill over first. Distill over last. Remain in the distillation flask. Decompose before reaching the top of the column. If a sample of an organic compound is suspected to be impure, which technique involves comparing its melting point with that of a known pure sample of the same compound? Mixed Melting Point Differential Scanning Calorimetry Fractional Crystallization Steam Distillation A mixture of Aniline (b.p. 184 C ) and Chloroform (b.p. 61 C ) can be separated most effectively by which of the following techniques? Simple Distillation Fractional Distillation Steam Distillation Sublimation A mixture of two compounds 'A' and 'B' is identified using the mixed melting point method. If 'A' is the pure compound and the unknown sample is also 'A', what happens to the melting point of the mixture? The melting point remains the same as that of pure 'A' The melting point decreases significantly The melting point increases significantly The mixture will not melt at a constant temperature Aniline is usually purified by which of the following methods? Steam distillation Simple distillation Sublimation Crystallization During distillation under reduced pressure, the boiling point of a liquid: Decreases as the pressure decreases Increases as the pressure decreases Remains constant regardless of pressure Becomes equal to its melting point Which of the following mixtures is best separated by the process of sublimation? Anthracene and Sodium Chloride Benzene and Toluene Sugar and Salt Ethyl alcohol and Water Which of the following is a specific type of fractionating column used in labs to provide a large surface area for heat exchange? Bubble plate column Carius tube Kjeldahl flask Liebig condenser In the crystallization of an organic compound, activated charcoal is sometimes added to the hot solution to: Remove colored impurities by adsorption Increase the boiling point of the solvent Act as a seed for crystal growth Prevent the decomposition of the compound The technique of 'seeding' is sometimes used in which purification process to initiate the formation of crystals? Crystallization Sublimation Distillation Chromatography Paper chromatography is an example of Partition chromatography Thin layer chromatography Column chromatography Adsorption chromatography On heating, some solid substances change from solid to vapour state without passing through liquid state. The technique used for the purification of such solid substances based on the above principle is known as Crystallization Sublimation Distillation Chromatography Which of the following methods is most suitable for the purification of glycerol? Distillation under reduced pressure Steam distillation Simple distillation Sublimation The purpose of using a fractionating column in fractional distillation is to: Provide many surfaces for heat exchange between ascending vapors and descending liquid Increase the boiling point of the liquid mixture Prevent the decomposition of the liquid Separate liquids that are immiscible Steam distillation is a variation of distillation used to separate substances that are: Steam volatile and immiscible with water Steam volatile and miscible with water Non-volatile and miscible with water Non-volatile and immiscible with water A mixture of naphthalene and benzoic acid can be separated by: Extraction with hot water Fractional distillation Crystallization from benzene Sublimation In steam distillation, the organic liquid boils at a temperature which is: Lower than its normal boiling point Higher than its normal boiling point Equal to its normal boiling point Equal to the boiling point of water Azeotropic mixtures (constant boiling mixtures) cannot be separated into their pure components by simple fractional distillation because: The composition of the liquid and vapor phases is identical The boiling points of the components are too far apart The components react chemically with each other They form a solid complex upon heating The molecular weight of a compound is twice its vapor density. If a compound has an empirical formula CH 2 and a vapor density of 21 , what is its molecular formula? C 3H 6 C 2H 4 CH 2 C 4H 8 A mixture of two liquids A (b.p. 350 K) and B (b.p. 355 K) can be best separated by which technique? Fractional distillation Simple distillation Steam distillation Vacuum distillation A mixture of ortho-nitrophenol and para-nitrophenol is separated by steam distillation. This is possible because: Ortho-nitrophenol is steam volatile due to intramolecular hydrogen bonding Para-nitrophenol is steam volatile due to intermolecular hydrogen bonding Ortho-nitrophenol has a higher boiling point than para-nitrophenol Para-nitrophenol is more soluble in water than ortho-nitrophenol Which of the following purification methods is used to separate 'spent lye' from glycerol in the soap industry? Distillation under reduced pressure Fractional crystallization Steam distillation Differential extraction Two compounds have the same empirical formula CH 2O . However, compound X has a vapor density of 30 and compound Y has a vapor density of 90 . What are their molecular formulas? X: C 2H 4O 2 , Y: C 6H 12 O 6 X: CH 2O , Y: C 3H 6O 3 X: C 2H 4O 2 , Y: C 4H 8O 4 X: C 3H 6O 3 , Y: C 9H 18 O 9 Hydrogen peroxide ( H 2O 2 ) is typically purified or concentrated using which of the following techniques to prevent its decomposition? Distillation under reduced pressure Steam distillation Simple distillation Fractional crystallization In steam distillation, the mixture of the organic liquid and water boils at a temperature T where the vapor pressures ( p 1 for water and p 2 for the organic liquid) and the atmospheric pressure ( P ) are related as: p 1 + p 2 = P p 1 = P p 1 - p 2 = P p 2 = P In the distillation of a mixture of two miscible liquids, the first fraction collected in the receiver will be richer in the component that has: A lower boiling point A higher boiling point A higher molecular weight A higher density The use of a fractionating column in fractional distillation increases the efficiency of separation because: It provides many 'theoretical plates' where multiple condensation and evaporation cycles occur It increases the atmospheric pressure inside the flask It lowers the boiling point of the higher-boiling component It prevents the formation of an azeotropic mixture A mixture of NaCl and KNO 3 can be separated using fractional crystallization. This is possible because: The solubility of KNO 3 increases significantly with temperature, while that of NaCl remains nearly constant NaCl is a covalent compound while KNO 3 is ionic NaCl sublimes upon heating while KNO 3 does not KNO 3 is more dense than NaCl Which technique is used to separate a mixture of two liquids with a boiling point difference of less than 25 K? Fractional distillation Simple distillation Steam distillation Distillation under reduced pressure Azeotropic mixtures are those which: Boil at a constant temperature like a pure liquid. Can be separated by simple distillation. Have very different boiling points. Are always composed of three components. What is the main advantage of using 'Distillation under reduced pressure' (Vacuum Distillation)? It allows liquids to boil at temperatures lower than their normal boiling points. It speeds up the distillation of high-boiling liquids. It prevents the decomposition of heat-sensitive compounds. All of the above. The separation of a mixture of liquids by 'Distillation under reduced pressure' is specifically employed for liquids which: Decompose at or below their normal boiling points Are highly volatile and have low boiling points Are immiscible with water Have very high boiling points but are stable The principle of 'Steam Distillation' is based on the fact that: The sum of the vapor pressures of the organic liquid and water equals the atmospheric pressure The organic liquid must be miscible with water The organic liquid boils at its normal boiling point The organic liquid must have a higher vapor pressure than water at 100 C Which technique is the most suitable for the separation of a mixture containing two volatile liquids having a boiling point difference of 15 K? Fractional distillation Simple distillation Steam distillation Vacuum distillation The 'Victor Meyer' method is commonly used for the determination of which property of an organic compound? Molecular mass of volatile liquids Percentage of nitrogen Empirical formula Melting point Which of the following statements regarding 'Vacuum Distillation' is correct? It allows a liquid to boil at a temperature lower than its normal boiling point. It is used for liquids that are stable at their normal boiling point. The external pressure is increased to facilitate faster evaporation. It is primarily used for the separation of two highly volatile liquids. A substance 'X' sublimes at 150 C. It is mixed with 'Y' which melts at 200 C and boils at 350 C. The best way to separate 'X' from 'Y' is: Sublimation Steam distillation Fractional crystallization Simple distillation In the Victor Meyer's method, 0.2 g of a volatile organic compound displaced 56 mL of air at STP. What is the molecular mass of the compound? 80 g/mol 40 g/mol 100 g/mol 60 g/mol In steam distillation, the organic liquid starts to boil when the sum of its vapor pressure ( p 1 ) and the vapor pressure of water ( p 2 ) becomes: Equal to the atmospheric pressure Greater than the atmospheric pressure Half of the atmospheric pressure Equal to the vapor pressure of the pure liquid During the purification of an organic compound by crystallization, the 'impurity' is expected to be: More soluble in the solvent than the compound at low temperatures. Less soluble in the solvent than the compound at all temperatures. Completely insoluble in the solvent. Volatile at the boiling point of the solvent. An organic compound has a vapor density of 45 and contains 40 % Carbon, 6.66 % Hydrogen, and 53.34 % Oxygen. What is its molecular formula? C 3H 6O 3 CH 2O C 2H 4O 2 C 6H 12 O 6 In the direct estimation of oxygen (Aluise method), the iodine produced is determined by titration. Which reagent is used to convert the evolved CO into CO 2 while simultaneously releasing iodine? Iodine pentoxide ( I 2O 5 ) Potassium permanganate Sodium peroxide Copper oxide The Victor Meyer method is used for the determination of the molecular mass of volatile organic compounds. The volume of which substance is measured in this method? Displaced air Evolved nitrogen gas Condensed vapor Vaporized liquid In fractional distillation, the efficiency of the separation of two volatile liquids is often expressed in terms of the number of: Theoretical plates Reflux ratios Boiling stages Condensation cycles A mixture of ethanol and water forms a 'minimum boiling azeotrope'. This means that the boiling point of the mixture is: Lower than the boiling points of both ethanol and water Higher than the boiling points of both ethanol and water Exactly the average of the boiling points of ethanol and water Equal to the boiling point of ethanol but lower than water The boiling point of a 1:1 mixture of two immiscible liquids, A (b.p. 100 C ) and B (b.p. 80 C ), at 1 atm will be: Below 80 C Between 80 C and 100 C Exactly 90 C Above 100 C What is the primary role of the 'air jacket' or 'glass jacket' in the Victor Meyer apparatus? To ensure a constant high temperature environment for the vaporizing tube To condense the vapors of the organic compound To collect the displaced air To measure the volume of the gas produced Sublimation is a process where a solid changes directly into vapor. Which of the following can be purified by sublimation? Camphor Sugar Sodium chloride Urea Which of the following describes the 'Theoretical Plate' concept in fractional distillation? A hypothetical zone where liquid and vapor phases reach equilibrium A physical metal plate inside the distillation flask The temperature at which the mixture starts to boil The ratio of the volume of the distillate to the residue In the process of crystallization, why is the hot saturated solution filtered through a fluted filter paper? To provide a larger surface area and prevent the solution from cooling and crystallizing in the funnel To remove the soluble impurities more effectively To increase the speed of evaporation of the solvent To ensure that only large crystals are formed in the filtrate The best method for the separation of naphthalene and benzoic acid from their mixture is - Sublimation Chromatography Crystallisation Distillation Sulphide ores of metals are usually concentrated by froth flotation process. Which one of the following sulphide ores offer an exception and its concentrated by chemical leaching ? Galena Copper pyrite Sphalerite Argentite Match List I with List II array llll ; & List-I; (Mixture) & ; & List-II; (Method of separation) A. & CHCl3 + C6H5NH2 & (I) & Distillation under reduced pressure B. & Crude oil in petroleum industry & (II) & Steam distillation C. & Glycerol from spent-lye & (III) & Fractional distillation D. & Aniline - water & (IV) & Simple distillation array Choose the correct answer from the options given below: A-III, B-IV, C-II, D-I A-IV, B-III, C-I, D-II A-IV, B-III, C-II, D-I A-III, B-IV, C-I, D-II Two products X and Y are formed in the following reaction sequence. The suitable method that can be used for the separation of products X and Y is : Continuous extraction Differential extraction Sublimation Fractional distillation In the estimation of oxygen in an organic compound by the Aluise method, the compound is decomposed in a stream of nitrogen gas. The mixture of gaseous products is passed over red-hot coke to convert all oxygen into: Carbon monoxide ( CO ) Carbon dioxide ( CO 2 ) Water vapor ( H 2O ) Oxygen gas ( O 2 ) During the estimation of nitrogen by the Dumas method, 0.25 g of an organic compound gave 40 mL of nitrogen collected at 300 K and 725 mm pressure. If the aqueous tension at 300 K is 25 mm, what is the volume of nitrogen at STP? 33.52 mL 36.84 mL 40.00 mL 44.12 mL In the direct estimation of oxygen (Aluise method), all the oxygen in the organic compound is converted into CO by passing it over red-hot coke. The CO is then oxidized to CO 2 using: Iodine pentoxide ( I 2O 5 ) Potassium permanganate ( KMnO 4 ) Copper(II) oxide ( CuO ) Concentrated nitric acid ( HNO 3 ) A mixture of camphor and benzoic acid can be separated by which of the following? Chemical method (using NaHCO 3 ) Sublimation Simple distillation Fractional distillation Which purification technique is most appropriate for the concentration of sugarcane juice in the sugar industry to prevent the decomposition of sugar? Distillation under reduced pressure Fractional distillation Steam distillation Simple distillation In steam distillation, if the organic liquid 'A' and water 'B' are distilled, the ratio of the masses of 'A' and 'B' in the distillate is given by ( p = vapor pressure, M = molecular mass): m A / m B = (p A M A) / (p B M B) m A / m B = (p A M B) / (p B M A) m A / m B = p A / p B m A / m B = M A / M B During the estimation of oxygen in an organic compound by the Aluise method, the iodine released is titrated against 0.05 M sodium thiosulfate. If 40 mL of thiosulfate is consumed for 0.16 g of the compound, what is the percentage of oxygen? (Stoichiometry: 1 mole O 1 mole CO 1 mole I 2 2 moles Na 2S 2O 3 ) 10 % 20 % 5 % 15 %