19. Calculate the emf of the following cell at 298 K:

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1 19. Calculate the emf of the following cell at 98 K: 3 Fe(s) Fe + + cell Given E = 0.44 V 0.001M H (1M) H (g) (1bar), Pt(s) Ans. At anode: Fe Fe + + e - At cathode: H + + e - H So, total number of electrons (n) transferred = Given: E o cell = Volt Temperature (T) = 98 K.303RT aoxi Ecell Ecell log nf ared V aoxidation V Ecell Ecell log Ecell 0.44 log n areduction 1 Therefore, E cell = 0.44( ) = = 0.53 Volt. 0. How would you account for the following? 3 Transition metals exhibit variable oxidation states. Zr (Z = 40) and Hf (Z = 7) have almost identical radii. Transition metals and their compounds act as catalyst. Complete the following chemical equations: Cr O 6Fe 14H CrO H MnO 5C O 16H Ans. The variable oxidation states of transition elements are due to the participation of ns and (n 1)d-electrons in bonding. Lower oxidation state is exhibited when nselectrons take part in bonding. Higher oxidation states are exhibited when (n 1) d-electrons take part in bonding. OR This is because the atomic radii of 4d and 5d transition elements are nearly same. This similarity in size is consequence of lanthanide contraction. Because of this lanthanide contraction the radii of Hf becomes nearly equal to that of Zr. Transition elements act as good catalyst in chemical reaction because they can lend electrons or withdraw electrons from the reagent, depending on the nature of the reaction. The ability of transition metals to be in a variety of oxidation states, the ability to interchange between the oxidation states and the ability to form

2 complexes with the reagents and be a good source for electrons make transition metals good catalysts. Complete the following equations: CrO H + Cr O H O OR MnO C O H + Mn CO + 8H O 1. (a) What type of semiconductor is obtained when silicon is doped with boron? 3 (b) What type of magnetism is shown in the following alignment of magnetic moments? (c) What type of point defect is produced when AgCl is doped with CdCl? Ans. (a) When silicon is doped with boron, p-type semiconductor is obtained. (b) The magnetism shown in the alignment of magnetic moments is ferromagnetism. (c) Impurity defect is produced when AgCl is doped with CdCl.. Determine the osmotic pressure of a solution prepared by dissolving.5 10 g of K SO 4 in L of water at 5 C, assuming that it is completely dissociated. 3 (R = L atm K 1 mol 1, Molar mass of K SO 4 = 174 g mol 1 ) Ans. w =.5 10 g (Mass of K SO 4 ) and M = 174 g mol 1 (Molar mass of K SO 4 ) V = L, R = L atm K 1 mol 1 and T = 5 C = 98 K w RT Osmotic pressure, MV atm.

3 3. Write the names and structures of the monomers of the following polymers: Polystyrene Dacron Teflon 3 Ans. Polymers with their monomers and their structures: Polymer Monomer Structure Polystyrene Styrene ( Vinyl benzene) Dacron 1. Ethylene glycol. Terepthalic acid 1.. Teflon Tetrafluoroethene CF =CF 4. (a) Which one of the following is a food preservative? 3 Equanil, Morphine, Sodium benzoate (b) Why is bithional added to soap? (c) Which class of drugs is used in sleeping pills? Ans. (a) Sodium benzoate is used as a food preservative whereas equanil is a tranquillizer and morphine is a narcotic analgesic. (b) Bithional is an antiseptic so it is added to soaps to reduce odours producing bacterial decomposition of organic matter on the skin. (c) Tranquillizers relieve stress, fatigue by inducing sense of well being, so they are used in the making of sleeping pills.

4 5. After watching a programme on TV about the adverse effects of junk food and soft drinks on the health of school children, Sonali, a student of Class XII, discussed the issue with the school principal. Principal immediately instructed the canteen contractor to replace the fast food with the fibre and vitamins rich food like sprouts, salad, fruits etc. This decision was welcomed by the parents and the students. 3 After reading the above passage, answer the following questions: (a) What values are expressed by Sonali and the Principal of the school? (b) Give two examples of water-soluble vitamins. Ans. (a) The values showed by Sonali are awareness regarding adverse effect of junk food and concern for the health of her school mates. The value showed by the principal is responsible behavior in listening to Sonali s views and taking prompt action in replacing junk food with healthy food. (b) The water soluble vitamins are vitamin B-complex and vitamin C. 6. Give the structures of A, B and C in the following reactions: 3 CuCN HO/H NH3 C6H5NCl A B C Sn HCl NaNO HCl HO/H C6H5NO A B C 73 K Ans.

5 7. Write the types of isomerism exhibited by the following complexes: [Co(NH 3 ) 5 Cl]SO 4 [Co(en) 3 ] 3+ [Co(NH 3 ) 6 ] [Cr(CN) 6 ] 3 Ans. Ionisation isomerism Optical isomerism Coordination isomerism