11th Class Chemistry Equilibrium / साम्यावस्था

  • question_answer 95)
    Determine the solubilities of silver chromate, barium chromate, ferric hydroxide, lead chloride and mercurous iodide at 298 K from the solubility product constant. Determine the molarities of individual ions. \[{{K}_{sp}}A{{g}_{2}}Cr{{O}_{4}}=1.1\times {{10}^{-12}}\] \[{{K}_{sp}}Fe{{(OH)}_{3}}=1\times {{10}^{-38}}\] \[{{K}_{sp}}PbC{{l}_{2}}=1.6\times {{10}^{-5}}\] \[{{K}_{sp}}H{{g}_{2}}{{I}_{2}}=4.5\times {{10}^{-29}}\]  

    Answer:

    Silver chromate: \[\underset{s}{\mathop{A{{g}_{2}}Cr{{O}_{4}}}}\,\to 2\underset{2s}{\mathop{A{{g}^{+}}}}\,+\underset{s}{\mathop{CrO_{4}^{2-}}}\,\] \[{{K}_{sp}}={{[A{{g}^{+}}]}^{2}}[CrO_{4}^{2-}]\] \[={{[2s]}^{2}}[s]=4{{s}^{3}}\] \[s={{\left[ \frac{{{K}_{sp}}}{4} \right]}^{1/3}}={{\left[ \frac{1.1\times {{10}^{-12}}}{4} \right]}^{1/3}}\] \[=6.5\times {{10}^{-5}}M\] \[[A{{g}^{+}}]=2\times 6.5\times {{10}^{-5}}M\] \[=13\times {{10}^{-5}}M\] \[[CrO_{4}^{2-}]=s=6.5\times {{10}^{-5}}M\] Similarly solubility of barium chromate can be calculated. Ferric hydroxide: \[\underset{s}{\mathop{Fe{{(OH)}_{3}}}}\,\to \underset{s}{\mathop{F{{e}^{3+}}}}\,+3\underset{3s}{\mathop{O{{H}^{-}}}}\,\] \[{{K}_{sp}}=[F{{e}^{3+}}]{{[3O{{H}^{-}}]}^{3}}\] \[=[s]{{[3s]}^{3}}=27{{s}^{4}}\] \[s={{\left[ \frac{{{K}_{sp}}}{27} \right]}^{1/4}}={{\left[ \frac{1\times {{10}^{-38}}}{27} \right]}^{1/4}}\](Solve using log table) \[=1.38\times {{10}^{-10}}M\] \[[F{{e}^{3+}}]=1.38\times {{10}^{-10}}M\] \[[O{{H}^{-}}]=3\times 1.38\times {{10}^{-10}}\] \[=4.14\times {{10}^{-10}}M\] Lead chloride: \[\underset{s}{\mathop{PbC{{l}_{2}}}}\,\to \underset{s}{\mathop{P{{b}^{2+}}}}\,+\underset{2s}{\mathop{2C{{l}^{-}}}}\,\] \[{{K}_{sp}}=[P{{b}^{2+}}]{{[C{{l}^{-}}]}^{2}}\] \[1.6\times {{10}^{-5}}=[s]{{[2s]}^{2}}\] \[1.6\times {{10}^{-5}}=4{{s}^{3}}\] \[s={{\left[ \frac{1.6\times {{10}^{-5}}}{4} \right]}^{1/3}}\] \[=0.0158\,M\] \[\therefore \]\[[P{{b}^{2+}}]=0.0158M,\,\,\,[C{{l}^{-}}]=2\times 0.0158\] \[=0.0316\,M\] Mercurous iodide: \[\underset{s}{\mathop{H{{g}_{2}}{{I}_{2}}}}\,\to \underset{s}{\mathop{Hg_{2}^{2+}}}\,+\underset{2s}{\mathop{2{{I}^{-}}}}\,\] \[{{K}_{sp}}=[H{{g}^{2+}}]{{[{{I}^{-}}]}^{2}}\] \[4.5\times {{10}^{-29}}=s{{[2s]}^{2}}=4{{s}^{3}}\] \[s={{\left[ \frac{4.5\times {{10}^{-29}}}{4} \right]}^{1/3}}\] \[=2.24\times {{10}^{-10}}M\] \[[Hg_{2}^{2+}]=2.24\times {{10}^{-10}}M\] \[[{{I}^{-}}]=2\times 2.24\times {{10}^{-10}}M\] \[=4.48\times {{10}^{-10}}M\]  


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