Question

On passing \[{{H}_{2}}S\] gas through a highly acidic solution containing \[C{{d}^{+2}}~\] ions, CdS is not precipitated because
(A) Of common ion effect
(B) The solubility of CdS is low
(C) \[C{{d}^{+2}}~\] ions do not form complex with \[{{H}_{2}}S\]
(D) Solubility product of CdS is low

Answer 1

Hint: The given solution is highly acidic means it contains a large number of hydrogen ions (An acidic solution is one in which protons released by acid are present in large amounts as compared to hydroxyl ions, released by base). On the other hand, \[{{H}_{2}}S\] gas which is also an acid whether it is weak acid does not dissociate in an acidic solution to give protons because acid and acid reaction does not take place.

Complete Step by Step Solution:
An acidic solution containing \[C{{d}^{+2}}~\] ions and when we add \[{{H}_{2}}S\] gas which is weak acid does not get dissociates into \[2{{H}^{+}}\]and\[{{S}^{2-}}\] as per hint. As it does not dissociate into ions so, \[C{{d}^{+2}}~\]cannot form a bond with \[{{S}^{2-}}\].

When two opposite ions, anion, and cation form bonds with each other they increase insoluble ionic product and it settles down to the base (precipitates) of the container containing solution and this is known as a precipitation reaction.

So, from this, we can conclude that the solution contains only \[C{{d}^{+2}}~\] ions and precipitate does not occur yet. The formation of a precipitate indicates that equilibrium is set between precipitates and ions soluble in solution. Thus, in this solution, the saturated point or equilibrium is not settled yet.

On reaching equilibrium, the product of the concentration of ions produced in solution is termed as solubility product which is a measure of the maximum number of ions that can dissolve in solution at the saturating point and others remain in precipitate form. But in this reaction equilibrium is not attained yet so we cannot conclude the total number of ions that can produce. So the product of the concentration of ions or can say solubility product is less.
Thus, the correct option is D.

Note: It is important to note that the value of solubility product does not depend on the concentration of products but depends on temperature and it is fixed for a particular reaction at a fixed temperature. Below its fixed value of ionic product, precipitation does not occur, if its fixed value attains in solution so, precipitation starts, and above its fixed value, the precipitation occurs at a good rate.