Chemistry_Today_April_2017_vk_com_stopthepress

Recommendations

Info

– 38. (a) : H 2 O ( Minor product) (Major product) 44. (b) : Chlorine has both +R-effect and –I effect but –I effect outweighs +R-effect. –I effect of chlorine atom disperses the –ve charge on the benzoate anion and thus, makes p-chlorobenzoate anion more stable. As a result, p-chlorobenzoic acid is a stronger acid than benzoic acid. 45. (b) 46. (c) 47. (d) : 4 th period has 18 elements. Filling of 4 th period is related with 4s, 3d and 4p. 48. (a) 49. (c) : Conductance increases with increasing temperature of a weak electrolyte. 50. (a) 51. (a) : If anion-anion contact retained, then Cl – according to the figure, C Li + Interionic distance of LiCl = a 2 = 514 . A ° Cl – = 2.57 Å Li + A B 2 BC = AB 2 + AC 2 = ( 257 . ) 2 + ( 2. 57) 2 = 3.63 Å Radius of Cl – ion = 1 2 BC = 1 2 × 3.63 = 1.82 Å 39. (a) : 40. (a) : T 1 is melting point at which entropy change is entropy of fusion. T 2 is boiling point at which entropy change is entropy of vaporisation. 41. (c) : Graphite is thermodynamically stable form of carbon at STP, so its standard enthalpy is zero, not of diamond. 42. (a) 43. (d) : But-1-ene and 2-methylprop-1-ene are chain isomers. Chain isomers have same molecular formula but different arrangement of carbon atoms. 52. (c) 53. (c) : 2 6 3 4 54. (d) : The radius of second orbit of He + is twice that of the first orbit of hydrogen. Bohr expression for radius of the electron in a particular orbit for hydrogen and hydrogen like species is 2 2 nh r n = 2 2 4π mZe 55. (a) : O C O, resultant dipole moment (µ) = 0. This shows that CO 2 is a linear molecule. 56. (a) 57. (a) 58. (d) : Only those chemicals which are added to food to improve its storing qualities, appearance, taste, odour and food value are called food additives. Preservatives do not increase the nutritive value of food. 59. (d) : Both the nitrogens are not basic. Only the lone pair of electrons on N(II) are involved in delocalisation. 60. (a) – CHEMISTRY TODAY | APRIL ‘17 51
CONCEPT MAP PERIODICITY IN PROPERTIES The basic object of classification is to arrange the facts regarding elements and their <strong>com</strong>pounds in such a way so that we may have greatest control over their characteristics with least possible effort. The repetition of similar physical and chemical properties of elements after regular intervals is known as periodicity in properties. Class XI Periodicity in Physical Properties Periodicity in Chemical Properties Ionic Radius · Across a period : The ionic radii of ions having same charge decreases as atomic number increases. · Down a group : Increases Li + < Na + < K + < Rb + < Cs + (Cations) F – < Cl – < Br – < I –(Anions) · Cationic radius < Atomic radius < Anionic radius (For isoelectronic species) · Z/e ratio increases, size decreases and vice-versa. Atomic Volume · Across a period : First decreases and then increases. Li , Be, B, C, N, O, F, Ne (cc/mol) 13 5 5 5 14 11 15 17 · Down a group : Increases Li, Na, K (cc/mol) 13 24 46 Density · Across a period : First increases and then decreases. Na, Mg, Al, Si, P, S (g/cm 3) 1.0 1.7 2.7 2.3 1.8 2.1 · Down a group : Decreases Be(1.8) , Mg(1.7) · Highest density solid : Os (22.6) · Highest density liquid : Hg (13.6) Atomic Radius · Across a period : Decreases Atomic radius µ 1/Z eff Li > Be > B > C > N > O > F · Down a group : Increases H < Li < Na < K < Rb < Cs · van der Waals' radius > Metallic radius > Covalent radius Electronegativity · Across a period : Increases Li < Be < B < C < N < O < F · Down a group : Decreases H > Li > Na > K = Rb > Cs · F is most electronegative element. Ionic Character · Across a period : First decreases and then increases. · Down a group : Increases Metallic Character · Across a period : Decreases · Down a group : Increases Ionisation Enthalpy · Across a period : Increases Li < Be > B < C < N > O < F · Down a group : Decreases H > Li > Na > K > Rb > Cs Valency · Across a period : Increases NaH < MgH 2 < AlH 3 < SiH4 · Down a group : Same Reducing Nature · Across a period : Decreases · Down a group : Increases Oxidising Nature · Across a period : Increases · Down a group : Decreases Strength of Oxyacids · Across a period : Increases H3BO 3 < H2CO 3 < HNO3 · Down a group : Decreases HNO 3 > H3PO 4 > H3AsO4 Acidity of Oxides · Across a period : Increases Na2O < MgO < Al2O 3 < SiO 2 < P2O 5 < SO 3 < Cl2O7 · Down a group : Decreases N2O 3 > P2O3 Acidity of Hydrides · Across a period : Increases CH 4 < NH 3 < H2O < HF · Down a group : Increases HF < HCl < HBr < HI Electron Gain Enthalpy · Across a period : More negative Li , Be, B, C, N, (kJ/mol) –60 +66 –83 –122 +31 O, F –141 –328 · Down a group : Less negative H , Li, Na, K, Rb, Cs (kJ/mol) –73 –60 –53 –48 –47 –46 Melting and Boiling Points · Across a period : M.pt. and B.pt. first increase and then decrease. Element : Na Mg Al Si P S M.pt. (K): 370.8 924 933 1693 317 392 B.pt. (K) : 1165 1396 2075 2815 557 717.6 · Down a group : They do show regular gradation but pattern of variation is different in different groups. Element : Li Na K Rb Cs M.pt. (K) : 454 370.8 335 312 302 B.pt. (K) : 1609 1165 1063 973 943
Page 2 and 3: Volume 26 No. 4 April 2017 Managing
Page 5 and 6: (R) K[Co(NH ) (NO ) 4 ] 1. The volu
Page 7 and 8: 24. m-Bromoaniline can be prepared
Page 9 and 10: (a) (b) (c) (d) CH CH C CH CH CH C
Page 11 and 12: 20. (d) : CH 2 5 alk. KMnO 4 ( A) C
Page 13 and 14: 41. (a) : According to Gibbs’-Hel
Page 15 and 16: 5. Compound 'X' C 7 H 8 O, is insol
Page 17 and 18: (c) (d) O HC 2 O O HC 2 O O CH CH C
Page 19 and 20: 4. As 2 S 3 sol carries a negative
Page 21 and 22: 15. Cl CHONa + EtOH 2 5 Heat Possib
Page 23 and 24: (c) If θ = 10°, the charge underg
Page 25 and 26: (c) (d) NH 2 O heat NH HO 2 C CO 2
Page 27 and 28: (c) Dil. HCl followed by reaction w
Page 29 and 30: 33. Which of the following reaction
Page 31 and 32: Balz-Schiemann reaction : tetrauoro
Page 33 and 34: 26. (c) : HC 3 HC 3 -H O CH 2 3 H +
Page 35 and 36: 12. At equimolar concentration of F
Page 37 and 38: (a) 1s 2 , 2s 2 2p 6 , 3s 2 3p 6 3d
Page 39 and 40: Fraction of M present as M 2+ = 88
Page 41: 26. (b) : According to Gay-Lussac
Page 49 and 50: Class XII This specially designed c
Page 51 and 52: JEE MAIN / JEE ADVANCED / PETs Only
Page 53 and 54: CHEMISTRY MUSING SOLUTION SET 44 24
Page 55 and 56: Isothermal reversible expansion :
Page 57 and 58: (a) H 2 O/H + , BH 3·THF/H 2 O 2·
Page 59 and 60: 22. H 2 can be obtained from 28. Th
Page 61 and 62: 7. Predict the product for the foll
Page 63 and 64: 7. (d) : Cyclopropane is under seve
Page 65 and 66: 46. If the first and the (2n - 1) t
Page 67 and 68: 1 (a) 6 2 ms − (b) 4 2 (c) 7 m s
Page 69 and 70: tension, viscous force, weight but
Page 71 and 72: (a) HN 2 SO 3 H (b) (NH 2 ) 2 CO (c
Page 73 and 74: SOLUTIONS PAPER-I 1. (a) : The phot
Page 75 and 76: 11. (a, d) : As, F 1 = k 1 x, F 2 =
Page 77 and 78: Given that, at equilibrium, ⎛ n
Page 79 and 80: 2 ∫ 53. (3) : (| x− 2| + [ x])
Page 81 and 82: percentage change in v = 1 2 perce
Page 83 and 84: Again, c 2 a 2 b 2 = + + 2a⋅b
Page 85: 90 CHEMISTRY TODAY | APRIL ‘17

Chemistry_Today_April_2017_vk_com_stopthepress

Create successful ePaper yourself

Delete template?

Save as template?