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NEET Sample Paper NEET Sample Test Paper-25

  • question_answer
    \[{{H}_{2}}S\]gas when passed through a solution of  cations containing HCl precipitates the cations of second group in qualitative analysis but not those belonging to the fourth group. It is because

    A)  the presence of HC1 decreases the sulphide ion concentration

    B)  the presence of HC1 increases the sulphide ion concentration

    C)  the solubility product of group II sulphides is more than that of group IV sulphides

    D)  the sulphides of group IV cations are unstable in HCl

    Correct Answer: A

    Solution :

     In qualitative analysis of cations of second group,\[{{H}_{2}}S\]gas is passed in the presence of HCl. Therefore, due to common ion effect, lower concentration of sulphide ions is obtained which is sufficient for the precipitation of second group cations in the form of their sulphides due to lower value of their solubility product \[({{K}_{sp}}).\] Here fourth group cations are not precipitated because they require more sulphide ions for exceeding their ionic product to their solubility products which is not obtained here due to common ion effect.


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