September 2011 - Career Point

UNDERSTANDINGInorganic Chemistry1. For SO 2 (g) at 273 K and 1 atm pressure, the dielectricconstant (or relative permittivity) is 1.00993. Thismolecule has a permanent dipole moment of 1.63 D.Assuming that SO 2 behaves as an ideal gas, calculateper mol of (a) total, (b) orientation, (c) inducedpolarizations, and (d) distortion polarizability.Sol. We haveεε r = = 1.00993ε 0p = 1.63 D = 1.63(3.3356 × 10 –30 Cm)V m = 22414 cm 3 mol –1 at 1 atm and 273 K(a) Total polarization,εr−1MP total =εr+ 2 ρ1.00993 −1=× 22.414 cm 3 mol –11.00993 + 2= 73.95 cm 3 mol –1(b) Orientation polarization,⎛2N ⎞AP 0 = ⎜p⎟3ε0 ⎝ 3kT⎠⎪⎧23{6.023×10 mol= ⎨−122⎪⎩ 3(8.854×10 C N−1−1}m−2⎪⎧−302(1.63×3.3356×10 Cm) ⎪⎫⎨−23−1⎬⎪⎩ 3(1.38×10 J K )(273K) ⎪⎭= 59.31 × 10 –6 m 3 mol –1 = 59.31 cm 3 mol –1(c) Induced polarization,P ind = P total – P 0= 73.95 cm 3 mol –1 – 59.31 cm 3 mol –1= 14.64 cm 3 mol –1(d) Distortion polarizability,Pindα d =(1/ 3ε)N0A–614.64×10 m mol=−122 −1−223 −1{1/(3×8.854×10 C N m )}(6.023×10 mol )= 6.46 × 10 –40 C 2 N –1 m2. A green coloured compound (A) gave the followingreactions :(i) (A) dissolves in water to give a green solution.The solution on reaction with AgNO 3 gives a whiteppt. (B) which dissolves in NH 4 OH solution andreappears on addition of dil. HNO 3 . It on heating with3−1⎪⎫⎬⎪⎭K 2 Cr 2 O 7 and conc. H 2 SO 4 produced a red gas whichdissolves in NaOH to give yellow solution (C).Addition of lead acetate solution to (C) gives ayellow ppt. which is used as a paint.(ii) The hydroxide of cation of (A) in borax bead testgives brown colour in oxidising flame and greycolour in reducing flame.(iii) Aqueous solution of (A) gives a black ppt. onpassing H 2 S gas. The black ppt. dissolves inaquaregia and gives back (A).(iv) (A) on boiling with NaHCO 3 and Br 2 water givesa black ppt. (D)(v) (A) on treatment with KCN gives a light greenppt. (E) which dissolves in excess of KCN to give(F). (F) on heating with alkaline bromine water givesthe same black ppt. as (D).Identify compounds (A) to (F) and give balancedequations of the reactions.Sol. Reaction (i) indicates that (A) contains Cl – ionsbecause, it gives white ppt. soluble in NH 4 OH. It isagain confirmed because it gives chromyl chloridetest. The colour of oxidising and reducing flamesindicate that (A) also contains Ni 2+ ions. Hence, (A)is NiCl 2 . The different reactions are :(i) NiCl 2 + 2AgNO 3 → 2AgCl + Ni(NO 3 ) 2AgCl + 2NH 3 → [ Ag(NH3)2 ] ClAg(NH 3 ) 2 Cl + 2HNO 3 →SolubleAgCl ↓ + 2NH 4 NO 3whiteppt.(B)The equations of chromyl chloride tests are :NiCl 2 + Na 2 CO 3 → 2NaCl + NiCO 34NaCl + K 2 Cr 2 O 7 + 6H 2 SO 4 → 4NaHSO 4 + 2KHSO 4+ 3H 2 O + 2 CrO 2 Cl 2CrO 2 Cl 2 + 4NaOH →Na 2 CrO 4 + (CH 3 COO) 2 Pb →Na 2CrO 4Yellowsolution(C)Redgas+ 2NaCl + 2H 2 OPbCrO 4 + 2CH 3 COONaYellowppt.(ii) Na 2 B 4 O 7 . 10H 2 O∆Na 2 B 4 O 7 + 10H 2 ONa 2 B 4 O∆7 2 NaBO1442 + B4442O3NiO + B 2 O 3Ni(BO 2 ) 2 + C∆∆Transparent beadNi (BO 2 ) 2 [Oxidising flame]Nickelmetaborate(Brown)Ni + B 2 O 3 + COGrey[Reducing flame]XtraEdge for IIT-JEE 39 SEPTEMBER 2011