11th Class Chemistry Chapter 2 Experimental Techniques in Chemistry Short Question Answers

Chemistry short QA

11th Class Chemistry Chapter 2 Experimental Techniques in Chemistry Short Question Answers Below

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1.Mention various experimental techniques which are used for the purification?
The techniques are as follows: (i) Filtration (ii)Crystallization (iii)Sublimation (iv) Solvent extraction It depends upon the nature of the substances that which technique is to be used.
2.How do you justify that qualitative and quantitative analysis are discussed in analytical chemistry?
It is that branch of chemistry which gives up analysis of elements and compounds.In qualitative analysis we come to know about nature of the elements and in quantitative analysis gives us the quantities of different elements in the compound.
3.Define sublimation with an example?
The vaporization of a solid directly on heating without passing through the liquid phase and the condensation of these vapors on coling to said without passing through liquid phase is called sublimation. Naphthalene iodine NH4CI, bezoic acid and camphor undergo.sublimation.We can do the separation of solids without using solvents.
4.How desiccator is used to dry the crystals?
The prepared crystals are wet and they need drying.In a desiccator the crystals are spread on the watch glass and placed in a desiccator for several hours.Some drying agents like anhydrous CaCI2,silica gel or P2O5 are used.
5.How does a Gooch crucible increase the rate of filtration?
This crucible is made up of porcelain.It has perforated base covered with a filter paper or asbestos mate.Filtration can be done quickly if this crucible is placed in a suction of filtering apparatus.
6.Concentrated HCI and KmnO4 solutions cannot be filtered by Gooch crucible.Give reason?
Conc. HCI and the oxidizing agents like KmnO4 react with filter paper.For this purpose the perforation of Gooch crucible is covered with asbestos mate.In this way the above solutions can be filtered.
7.Which solvents are mostly used in crystallization?
The most commonly used solvents are: (i) Water (ii)Rectified spit (iii)Absolute alcohol (iv)Ether(v)Acetone (vi)Chloroform (vii)CCl4 (viii)Acetic acid (ix)Petroleum ether.
8.Give the main characteristics of the solvent used for crystallization.
(i) The solvent should dissolve a large amount of slut at high temperature. (ii)The solvent should have no chemical reaction with solute. (iii)It should bot dissolve the impurities. (iv) It should be cheap. (v)It should not be inflammable.
9.Mention the major steps involved in the crystallization?
(i)Preparing the saturated solution. (ii)Filtering the impurities. (iii)Cooling of the filtrate. (iv)Collection of crystals. (v)Drying of crystals.
10.How the decolonization of undesirable colors and dehydration is carried out for freshly prepared crystalline substances?
The decolonization of undesirable color is carried out by boiling the substance with sufficient amount of powdered animal charcoal in the solvent.Hot solution is filtered.In this way charcoal abosords the colored impurities and the pure decolonized substance crystallizes on cooling.The dehydrating agents employed are conic.H2So4,P2O5 or silica gel.
11.What is solvent extraction?
This is technique in which a solute is separated from the solution.For this purpose the solution is shaken with another solvent in which the solute is more soluble.Anyhow the added solvent should not be miscible with the solution.
12.What is ether extraction?
Some organic products are prepared in aqueous medium.We have to remove this organic compound from water.For this purpose ether is added.Two separate layers are produced in the separating funnel.The ether layer contains the organic compound.This ether layer is separated and ether is evaporated.
13.What is Rf value ? Give its units?
14.Give the main uses of paper chromatography?
(i) For the separation and purification of colored organic compounds. (ii)For checking the purity of the compounds. (iii)In qualitative and quantitative analysis. (iv)For the separation purification and identification of products of reactions.
15.Differentiate between stationary and mobile phase?
The solvent or the mixture of solvents used for the separation of components in chromatography is called mobile phase.The phase over which mobile phase flows is stationary one.Water ethyl alcohol etc are some important mobile phases while silica gel and filter paper are some important stationary phases.
16.What is the distribution coefficient?To which technique it is applicable?
17.How naphthalene can be purified?
Naphthalene can be directly converted from solid to vapor state i.e. by the sublimation.The impurities as left behind because they do not sublime.Inverted funnel can be used.
18.In solvent extraction technique repeated extractions using small portions of solvent are more efficient than using a single extraction but larger volume of solvent.Why?
It is to constant value of distribution coefficient of a solute in two solvents,which are insoluble.Say an organic solute is 1g,and is present in 1000 ml of H2o.We have 1000 ml of ether for extraction.If we use 1000 ml ether in one installment 67% of 1g of solute is extracted if KD is 2 in the favor of ether.But by using two installments of 500 ml each 75% of 1g is extracted and so on.
19.Why is there a need to crystallize a crude product?
Impurities are mostly present in the crude product.By using a suitable solvent in which the required substance under preparation is soluble is used to get the crystals o f that substance.The crystals are a pure substance.
20.Iodine is more soluble in water in presence of KI.Give reason?
To dissolve I2 in water a dilute solution KI should be prepared first of all.I2 combines with I of KI to give I3 ion.This ion I3 is soluble in water.I2 is not soluble in H2O.
21.How crystals are dried using filter paper?Give its two disadvantages?
Ans:The crystals of substance after filtration in the same filter paper.Then dry filter papers are pressed on the wet filter paper having crystals.This is repeated again and again by using many dry filter papers. The main disadvantage is that crystals are not perfect dry.

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