Principles Of Qualitative Analysis NEET PYQs (2005–2026) with Solutions

1 solved Principles Of Qualitative Analysis PYQs

Real NEET and AIPMT questions from this chapter, newest first. Try each one, then open the answer and the step-by-step explanation.

1. Question 1 (AIPMT 2005)

   AIPMT 2005MediumCommon Ion Effect and Group Separation

   $H_2S$ gas when passed through a solution of cations containing $HCl$ precipitates the cations of second group of qualitative analysis but not those belonging to the fourth group. It is because:

   1. AOption A: presence of $HCl$ decreases the sulphide ion concentration
   2. BOption B: presence of $HCl$ increases the sulphide ion concentration
   3. COption C: solubility product of group II sulphides is more than that of group IV sulphides
   4. DOption D: sulphides of group IV cations are unstable in $HCl$

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   Correct answer: (A) presence of $HCl$ decreases the sulphide ion concentration

   Explanation

   $HCl$ suppresses the ionisation of $H_2S$ due to common ion effect: $$H_2S \rightleftharpoons 2H^+ + S^{2-}$$ Increase in $H^+$shifts equilibrium to the left, decreasing$[S^{2-}]$. Only highly insoluble group II sulphides precipitate at this low sulphide ion concentration, whereas group IV sulphides do not. Hence option (A) is correct.