Tiêu đề DPP-8 SOLUTION.pdf ✅

CLASS : XIth SUBJECT : CHEMISTRY DATE : DPP No. : 8 1 (a) The presence of excess of sulphur makes sodium thiosulphate a useful reducing agent. 2Na2S2O3 + I3 →Na2S4O6 + 2NaI This reaction is applied in volumetric estimation of iodine. In this reaction sodium thiosulphate acts as a reducing agent. 2 (b) The alkaline earth metal salts do not contain unpaired electrons. 3 (c) Molten NaCl has Na + and Cl ― ions. 4 (a) Ag and Hg oxides decompose on heating. 5 (c) When a few drops of FeCl3 solution is added to hypo solution, a violet colour of ferric thiosulphate is obtained. 3Na2S2O3 + 2FeCl3 ⇌Fe2 (S2O3 )3 + 6NaCl violet colour This colour disappears quickly due to reduction of ferric chloride by thiosulphate. 2FeCl3 + 2Na2S2O3 →2FeCl2 + Na2S4O6 + 2NaCl 6 (d) High blood pressure is developed if Na + becomes more in human blood. 7. (a) Li2CO3 decomposes on heating: Li2CO3⟶Li2O + CO2. 8 (d) NaCl + H2O⟶Na +(aq) + Cl ―(aq) 9 (d) Formula of gypsum = CaSO4. 2H2O Formula of plaster of Paris = CaSO4 . 1 2 H2O Topic :- THE S-BLOCK ELEMENTS Solutions
Difference of water molecule = 2H2O –1 2 H2O = 1 1 2 H2O 10 (b) 226 88 Ra⟶222 86 Rn + 4 2He 11 (a) Effective nuclear charge (ENC) of K + > ENC of Cl ― and thus, shells are pulled more effectively in K + ion. 12 (a) The lattice energy of alkali metal halides decreases down the group due to increase in size of alkali metals. Thus, LiCl NaCl KCl RbCl CsCl 883 ͦC 808 ͦC 772 ͦC 717 ͦC 645 ͦC 13 (c) Na + NH3⟶NaNH2 + 1 2 H2 14 (a) Alkali metals are strongest reducing agent among elements of Periodic Table. The reducing character decreases down the group. ∴ Li is strongest reducing agent among Li, Na, Mg and Ca. 15 (d) Due to small size of Na +, it is heavily hydrated and become large molecule. Ionic conductance increases down the group in alkali metals. Order of ionic conductance Na + < K + < Rb + < Cs + 16 (c) The only reaction in which carbon monoxide (a neutral oxide of carbon) acts as an acid. 17 (b) Be and Mg salts possess covalent nature. 18 (c) Beryl is an ore of Be, i.e., (BeO). 20 (d) These are various names for NaCl. CO + NaOH 200 0C High P HCOONa
ANSWER-KEY Q. 1 2 3 4 5 6 7 8 9 10 A. A B C A C D A D D B Q. 11 12 13 14 15 16 17 18 19 20 A. A A C A D C B C C D