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JEE Main 201212 MayOnline
Exam
JEE Main
Year
2012
Date
12 May
Mode
Online
Subject
Chemistry
Chapter
Chemical Equilibrium

JEE Main 2012 · 12 May · Online · Chemistry · Chemical Equilibrium

Given (i) HCN(a q)+H_2 O(b) leftharpoons H_3 O^ + (a q)+CN^ - (a q)...

Given (i) HCN⁡(aq)+H2O(b)⇌H3O+(aq)+CN−(aq)\operatorname{HCN}(a q)+\mathrm{H}_2 \mathrm{O}(b) \rightleftharpoons \mathrm{H}_3 \mathrm{O}^{+}(a q)+\mathrm{CN}^{-}(a q) Ka=6.2×10−10K_{\mathrm{a}}=6.2 \times 10^{-10} (ii) CN−(aq)+H2O(l)⇌HCN(aq)+OH−(aq)\mathrm{CN}^{-}(a q)+\mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightleftharpoons \mathrm{HCN}(a q)+\mathrm{OH}^{-}(a q) Kb=1.6×10−5K_{\mathrm{b}}=1.6 \times 10^{-5}. These equilibria show the following order of the relative base strength,

Options

  1. AOH−>H2O>CN−\mathrm{OH}^{-}>\mathrm{H}_2 \mathrm{O}>\mathrm{CN}^{-}
  2. BOH−>CN−>H2O\mathrm{OH}^{-}>\mathrm{CN}^{-}>\mathrm{H}_2 \mathrm{O}
  3. CH2O>CN−>OH\mathrm{H}_2 \mathrm{O}>\mathrm{CN}^{-}>\mathrm{OH}
  4. DCN−>H2O>OH−\mathrm{CN}^{-}>\mathrm{H}_2 \mathrm{O}>\mathrm{OH}^{-}

Correct answer

B. OH−>CN−>H2O\mathrm{OH}^{-}>\mathrm{CN}^{-}>\mathrm{H}_2 \mathrm{O}

Step-by-step solution

The more is the value of equilibrium constant, the more is the completion of reaction or more is the concentration of products i.e. the order of relative strength would be OH−\mathrm{OH}^{-}>CN−\mathrm{CN}^{-}>\mathrm{H}}_{2} \mathrm{O}
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