19. Define the following terms giving an example of each: 3 (i) Associated colloids (ii) Lyophilic sol (iii) Adsorption

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1 19. Define the following terms giving an example of each: 3 (i) Associated colloids Lyophilic sol (iii) Adsorption Ans. i. Associated colloids: There are some substances which at low concentration behave as normal strong electrolytes but at higher concentrations exhibit colloidal behaviour due to the formation of aggregates. The aggregated particles thus formed are called micelles or associated colloids. For e.g. grease droplet surrounded by stearate ions. ii. Lyophilic sol: Lyophilic means liquid-loving colloidal sols directly formed by mixing substances like gum, gelatine etc. with a suitable liquid (the dispersion medium) are called lyophilic sols. If the dispersion medium is separated from dispersed phase (say by evaporation), the sol can be reconstituted by simply remising with the dispersion medium that is why these sols are also known as reversible sols. iii. Adsorption: The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is known as adsorption. The molecular species which accumulates on surface is termed as adsorbate and the material on the surface of which the adsorption takes place is called adsorbent. For e.g. aqueous solution of raw sugar, when passed over beds of animal charcoal, becomes colourless as the colouring substances are adsorbed by the charcoal. 0. Calculate the emf of the following cell at 5 C : Ag s Ag 10 M Cu 10 M Cu s Given E cell = V and log 10 n = n. Ans. Ag (s) Ag + (10 3 M) Cu + (10 1 M) Cu(s) E 0.46V cell T = 98 K RT Oxidised species Ecell E cell ln nf Reduced species Cell reaction: Ag s Cu Ag Cu s n = aq Ecell 0.46 log log Ecell 0.61V aq 1

1. Shanti, a domestic helper of Mrs. Anuradha, fainted while mopping the floor. Mrs. Anuradha immediately took her to the nearby hospital where she was diagnosed to be severely anaemic.

2 1. Shanti, a domestic helper of Mrs. Anuradha, fainted while mopping the floor. Mrs. Anuradha immediately took her to the nearby hospital where she was diagnosed to be severely anaemic. The doctor prescribed an iron rich diet and multivitamins supplement to her. Mrs. Anuradha supported her financially to get the medicines. After a month, Shanti was diagnosed to be normal. 3 (i) What values are displayed by Mrs. Anuradha? Name the vitamin whose deficiency causes pernicious anaemia. (iii) Give an example of a water soluble vitamin. Ans. (i) Mrs. Anuradha displayed values like concern, care and help by being with her domestic helper in her unfortunate moments. Deficiency of Vitamin B 1 causes Pernicious anaemia. (iii) B group vitamins and Vitamin C are water soluble vitamins.. Write the man products of the following reactions: 3 H3PO HO (i) C6H5NCl? Br NaOH (iii) CH 3 C NH? O Ans. (i) Products are Benzene, Nitrogen gas, Phosphorous acid and Hydrochloric acid. (iii) Products is,4,6-tribromoaniline Br NaOH CH 3 C NH CH 3 NH Na CO3 NaBr H O O Products are Methanamine, Sodium carbonate, Sodium bromide and Water.

3 3. The rate of a reaction becomes four times when the temperature changes from 93 K to 313 K. Calculate the energy of activation (E a ) of the reaction assuming that it does not change with temperature. [R = J K 1 mol 1, log 4 = 0 601] 3 Ans. Given: T 1 = 93 k; T = 313 k; R = J k 1 mol 1 ; k = 4k 1 ; E a =? The formula used is; k E a 1 1 log k 1.303R T 1 T Substituting values, we get log 4k1 Ea 1 1 k Jk 1 mol 1 93k 313k log 4 1 E 313k 93k Jk mol 93k 313k a Jk mol 93k 313k Ea 0k 1, 057, Ea Jmol kj mol 1 4. For the complex [NiCl 4 ], write 3 (i) the IUPAC name. the hybridization type. (iii) the shape of the complex. (Atomic no. of Ni = 8) OR What is meant by crystal field splitting energy? On the basis of crystal field theory, write the electronic configuration of d 4 in terms of t g and e g in an octahedral field when (i) Δ 0 > P Δ 0 < P Ans. [NiCl 4 ] (i) IUPAC name = Tetrachloronickelate (II) ion Hybridization of Ni in the complex [NiCl 4 ] is sp 3. The hybridisation scheme is shown in the following diagram. 3

4 Hence the hybridisation of Ni + in the complex is sp 3 (iii) As the hybridization of Ni is sp 3 so, shape of the complex is tetrahedral. OR Crystal Field Splitting Energy On the basis of crystal field theory, the approaching asymmetric field of ligands destablises the five degenerate d-orbitals of transition metal and causes splitting of these orbitals into a triply degenerate, t g orbital and a doubly degenerate, e g orbital. The difference of energy between these two sets of d-orbitals is called crystal field splitting energy or crystal field stabilization energy (CFSE). For example, in octahedral complex. For electric configuration of d 4 (i) When 0 > P Electronic configuration is 4 0 t geg 4

5 When o < P Electronic configuration is t eg 3 1 g 5. Give reasons for the following : 3 (i) Ethyl iodide undergoes S N reaction faster than ethyl bromide. (±) -Butanol is optically inactive. (iii) C X bond length in halobenzene is smaller than C X bond length in CH 3 X. Ans. (i) Ethyl iodide undergoes S reaction faster than ethyl bromide because the bond N length of C I in H C C Br H C C I as size of I is greater than Br. is greater than the bond length of C Br in As bond length is greater, bond energy required to break the C I bond is lesser and so it becomes easy to break the C I bond and I - (better leaving group) is released at a faster rate in the presence of incoming nucleophile. (±) -Butanol is optically inactive because it is both dextrorotatory i.e. (+) and laevorotatory i.e. ( ) and hence forms a racemic mixture in which the net rotation of plane polarized light towards right is cancelled by the left one and so it becomes optically inactive. (iii) C X bond length in halobenzene is smaller than C X bond length in CH 3 X because in halobenzene the C X acquires partial double bond character due to resonance as shown below where as in CH 3 X there is no such resonance. As the bond length of double bond is smaller than single bond hence C X bond length in halobenzene is smaller. 5

6 6. (i) What class of drug is Ranitidine? If water contains dissolved Ca + ions, out of soaps and synthetic detergents, which will you use for cleaning clothes? (iii) Which of the following is an antiseptic? 3 0.% phenol, 1% phenol Ans. i. Ranitidine belongs to Antihistamines class of drugs. ii. iii. If water contains Ca + ions then out of soaps and synthetic detergents, we will use synthetic detergents. In case of soaps, Ca + ions form insoluble calcium soaps when sodium or potassium soaps are dissolved in hard water. C H COONa CaCl NaCl C H COO Ca Soap Insoluble calcium sterate (Soap) Where as the synthetic detergents can be used in both soft and hard water. 0.% phenol is an antiseptic. 7. Give reasons for the following : 3 (i) Oxygen is a gas but sulphur is a solid. O 3 acts as a powerful oxidising agent. (iii) BiH 3 is the strongest reducing agent amongst all the hydrides of Group 15 elements. Ans. i. Oxygen forms O which is a gas and sulphur forms S 8 which is solid this can be explained as: Due to small size of oxygen, it has less tendency for catenation and high tendency of pπ-pπ multiple bonds, hence forms stable O molecules whereas sulphur because of its higher tendency for catenation and lesser tendency to form pπ-pπ multiple bonds forms S 8 molecules having 8-membered puckered ring. ii. Ozone is not a very stable compound under normal conditions and decomposes readily on heating to give a molecule of oxygen and nascent oxygen. Nascent oxygen, being a free radical, is very reactive. O O O 3 ozone oxygen Nascent oxygen Therefore, O 3 acts as powerful oxidizing agent. iii. BiH 3 is the strongest reducing agent amongst all the hydrides of group-15 elements because as we more down the group, the atomic size increases and the stability of the hydrides of group 15 element decreases. Since the stability of hydrides decreases on moving from NH 3 to BiH 3, the reducing character of the hydrides increases on moving from NH 3 to BiH 3. 6

Sure-Shot Questions- Chemistry Class XII

Sure-Shot Questions- Chemistry Class XII 1MARK 1 Of physisorption or chemisorption, which has a higher enthalpy of adsorption? 2 Rearrange the following compounds in the increasing order of their boiling