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VIT Engineering VIT Engineering Solved Paper-2015

  • question_answer
    A saturated solution of H2S in 0.1 M HCl at       25°C contains \[{{S}^{2-}}\]ion concentration of        \[{{10}^{-23}}\] mol \[{{L}^{-1}}\]. The solubility product of some sulphides  are  \[CuS={{10}^{-44}},\]\[FeS={{10}^{-14}},\]\[MnS={{10}^{-15}},\]\[CdS={{10}^{-25}}.\]If 0.01 M solution of these salts in 1M HCl are saturated with \[{{H}_{2}}S,\]which of these will be precipitated?

    A) AIl                          

    B) All except MnS

    C) All except MnS and FeS

    D) Only CuS

    Correct Answer: C

    Solution :

    \[\therefore \] \[\left| \frac{\Delta p}{p} \right|=\left| \frac{\Delta \lambda }{\lambda } \right|\] Ionic product, \[\Rightarrow \], Ionic product is greater than \[\frac{p'}{p}=\frac{0.20}{100}=\frac{1}{500}\] of CuS and CdS. Hence, these are precipitated. N                ote         (i) \[\Rightarrow \] the saturation limit has not reached, no precipitate will from and some can be dissolved.                  (ii) \[{{E}_{0}}.\] saturation limit has been exceeded and some precipitate will form in order to restore equilibrium.


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