Q.1.     What is analytical chemistry?

Ans.     Analytical chemistry is the science of chemical characterization of compounds and it includes both qualitative and quantitative analysis.

Q.2.     What is qualitative analysis?

a)         the analysis which is concerned with the detection or identification of elements present in a compound is called qualitative analysis.

Q.3.     Define Quantitative analysis?

Ans.     The analysis which involves the determination of the relative amounts of the substances present in a sample is called quantitative analysis.

Q.4.     What are the four major steps in quantitative analysis?

Ans.     The four major steps in quantitative analysis are:

  1. Obtaining a sample for analysis
  2. Separation of desired constituents
  3. Measurement, and calculation of results
  4. Drawing conclusion from the analysis.

Q.5.     What is meant by filtration?

Ans.     The process of separation of insoluble particles from liquids by passing the mixture through a filter media is called filtration.

Q.6.     Define sublimation with an example?

Ans.     The process in which a solid, when heated, vapourizes directly without passing through the liquid state and these vapours can be condensed to form the solid again is called sublimation. Naphthalene, NH4Cl, iodine and camphor undergo sublimation.

Q.7.     Which solvents are mostly used in crystallization?

Ans.     The solvents which are mostly used for crystallization are: (i) water (ii) rectified spirit, (iii) absolute alcohol, (iv) diethyl ether (v) acetone (vi) CCl4 (vii) Chloroform (viii) acetic acid (ix) Petroleum ether.

Q.8.     what is the difference between sublimation and condensation?

Ans.     The change of a solid directly to the vapour is called sublimation, while the change of a gas to either the liquid or the solid is called condensation.

Q.9.     How desiccator is used  to dry the crystals?

Ans. The crystals are spread over a watch glass and kept in a vacuum desiccator for several hours. The drying agents used in a desiccator are CaCl2, silica gel or P2O5.

Q.10.   How the decolourization of undesirable colours is carried out for freshly prepared crystalline substance?

Ans.     The decolourization of undesirable colour is carried out by boiling the substance in the solvent with the sufficient quantity of finely powdered animal charcoal and then filtering the hot solution. The animal charcoal adsorbs the coloured impurities and the pure decolourized substance crystallizes out form the filtrate on cooling.

Q.11.   Give the main characteristics of the solvent used for crystallization.

Ans.     An ideal solvent should have the following characteristics.

  1. The solvent should dissolve a large amount of the substance at its boiling point but only a small amount at room temperature.
  2. It should not react chemically with the solute.
  3. It should not dissolve the impurities.
  4. It should be chcap.
  5. On cooling it should deposit well-formed crystals of the pure compound.
  6. It should not be inflammable and should be easily removable.

Q.12.   Mention the major steps involved in the crystallization.

Ans.     (i) selection of suitable solvent (ii) preparation of saturated solution (iii) Removal of insoluble impurities by filtering the hot saturated solution. (iv) cooling the hot filtered solution (v) collection of crystals (vi) Drying the crystals.

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Q.13.   What is the basic principle of crystallization?

Ans.     The basic principle of crystallization is that the solute should be soluble in a suitable solvent at high temperature and the excess amount of the solute is thrown out as crystals when it is cooled.

Q.14.   Why is there a need to crystallize the crude product?

Ans.     The crude product is impure, therefore, there is a need to purify it by crystallization from a suitable solvent.

Q.15.   Define crystallization.

Ans.     The process in which a dissolved solute comes out of solution and forms a crystalline solid is called crystallization.

Q.16.   If the solvent is inflammable what precaution should be taken while heating the solution?

Ans.     Water bath should be used for heating purpose, so that solvent does not catch fire.

Q.17.   Why does the size of particles in the precipitate decide which type of filter paper should be used?

Ans.     The filter papers are available in a variety of porosities (pore sizes) and which pore size to be used, depend upon the size of particles in the precipitate.

Q.18.   Which points should be kept in mind while folding of filter paper?

Ans.     The following points should be kept in mind while folding of filter paper:

  • The filter paper should be folded twice. The first fold should be along the diameter of the paper. The second fold should be such that edges do not quite match.
  • The paper should be opened on the slightly larger section in order to get a cone with three fold thickness halfway around and one of thickness the other halfway around and an apex angle slightly greater than 60o.

Q.19.   What is Gooch crucible? How does it increase the rate of Filtration?

Ans.     It is made of porcelain having a perforated bottom which is covered with paper pulp or asbestos mat. For quick filtration, Gooch crucible is placed in a suction filtering apparatus to increase the rate of reaction.

Q.20.   What is sintered glass crucible?

Ans.     Sintered glass crucible is a glass crucible with a porous glass disc sealed into the bottom.

Q.21.   What is solvent extraction?

Ans.     A technique in chemical analysis by which a solute can be separated from a solution by shaking the solution with another solvent in which the solute is more soluble and the added solvent is immiscible with the solution is called solvent extraction.

Q.22.   What is ether extraction?

Ans.     The ether extraction is used to separate the products of organic synthesis from water. The aqueous solution containing the organic product is shaken with ether in a separating funnel and allowed to separate the two layers. The ether layer containing the organic compound is separated and the organic product is obtained by evaporating the ether.

Q.23.   Define distribution law or partition law?

Ans.     This law states that a solute distributes itself between two immiscible liquids in a constant ratio of concentrations irrespective of the amount of solute added.

Q.24.   In solvent extraction technique, why repeated extraction using small portions of solvent are more efficient than using a single extraction but larger volume of solvent?

Ans.     This is because more amount of solute is obtained by repeated extractions using small portions of volume of solvent that a single extraction using larger volume of solvent.

Q.25.   what is the distribution coefficient? To which technique it is applicable?

Ans.     It is a constant which is a ratio of concentration of solute in two immiscible solvents at equilibrium at a constant temperature.

KD =

The constant KD is called distribution coefficient. It is applicable to solvent extraction technique.

Q.26.   What is chromatography?

Ans.     Chromatography is a technique which is used for the separation of components of a mixture. It involves the distribution of solute between a stationary phase and a mobile phase.

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Q.27.   differentiate  between stationary phase and mobile phase.

Ans.     The stationary phase may be a solid or a liquid supported as a thin film on the surface of an inert solid, while the mobile phase flows over the surface of stationary phase. It may be a gas or a liquid. The solvent or mixture of solvents used for the separation of components of a  mixture in chromatography is called mobile phase. The phase over which the mobile phase flows is called stationary phase.

Q.28.   what if Rf value?

Ans.     Rf stands for retardation factor. Each component in the mixture has a specific retardation factor called Rf value. The Rf value is related to the distribution coefficient and is given by:

Rf =

Q.29.   Differentiate between adsorption chromatography and partition chromatography?

Ans.     (1)        Chromatography, in which the stationary phase is a solid, is called adsorption chromatography, while in which the stationary phase is a liquid is called partition chromatography.

(2)        in adsorption chromatography, a substance leaves the mobile phase to become adsorbed on the surface of the solid phase, e.g; column chromatography, while in partition chromatography the substances being separated are distributed throughout both the stationary and mobile phases, e.g., paper chromatography.

Q.30.   Why the substances are separated in chromatography? OR what principle is involved in chromatography?

Ans.     The substances are separated due to their relative affinities (attractions) for the stationary and mobile phases. The distribution of  the components of a mixture between the two phases is governed by the partition coefficient, K

K =

The component having smaller value of k mostly remains in the stationary phase as the mobile phase flows over it. The component with a greater value of K remains largely dissolved in the mobile phase and quickly passes over the stationary phase.

Q.31.   You have been provided with a mixture containing three inks with different colours. Write down the procedure to separate the mixture with the help of paper chromatography.

Ans.     Procedure. Take a strip of whatmann filter paper and draw a thin pencil line about 2.5 cm from one end on it. Spot a point, on the pencil line, with the given ink mixture solution. Pour a solution methanol and water as solvent into a chromatographic tank. Suspend the dried filter paper with clips in such a way that the impregnated end dips into a solution of methanol and water to a depth of 5-6 mm. cover the tank. As the solution (solvent front) creeps up the paper, the ink moves upward, separating into three different coloured bands. When the solvent front has risen to about 3/4th of the length of the paper, remove the strip, mark the solvent front with a pencil and allow the strips to dry. Calculate Rf values of the three different coloured as follow.

Rf =

Q.32.   A solid organic compound is soluble in water as well as in chloroform. During its preparation, it remains in aqueous layer describe a method to obtain it from this layer?

Ans.     The compound can be obtained by solvent extraction technique from aqueous layer. Take the aqueous solution containing the organic compound and chloroform in a separation of two layers. Since the organic compound will go into chloroform layer. The chloroform layer is separated and the organic compound is obtained by evaporating the chloroform.

Q.33.   A water insoluble organic compound is prepared by the reaction of salicylic acid with a mixture of acetic acid and acetic anhydride. How will you separate the product from the reaction mixture.

Ans.     The reaction mixture is poured into cold water in order to precipitate aspirin. It is then filtered through a Gooch crucible using a vacuum pump. The product is then crystallized from a mixture of equal volumes of water and acetic acid to get the crude product. The crude product, when completely dried, is re-crystallized from benzene to get pure aspirin.

Q.34.   Mention various experimental techniques with are used for the purification of substances.   

Ans.     The experimental techniques that are used for the purification of substance are: (i) Filtration (ii) Crystallization (iii) Sublimation (iv) solvent extraction. (v) the technique to be used depend upon the nature of the substances for the purification.

Q.35.   Why solid iodine sublimes. Give reason?

Ans.     Solid iodine has only dispersion forces, which are the weakest force. The vapour pressure of iodine is also low. Therefore, solid iodine sublimes.

Q.36.   What is the role of stationary phase in chromatography?

Ans.     The role of stationary phase in chromatography is to attract the components of the mixture and allow them pass over it with different strengths of attraction.

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