Question

The flocculating power of the given ions for the specified colloidal sols will be such that
(A) Arsenic sulphide sol : ${{\left[ Fe{{\left( CN \right)}_{6}} \right]}^{4-}}$ > $P{{O}_{4}}^{3-}$ > $S{{O}_{4}}^{2-}$ > $C{{l}^{-}}$
     Ferric hydroxide sol : $A{{l}^{3+}}>B{{a}^{2+}}>N{{a}^{+}}$
(B) Arsenic sulphide sol : $A{{l}^{3+}}>B{{a}^{2+}}>N{{a}^{+}}$
     Ferric hydroxide sol : \[~\] ${{\left[ Fe{{\left( CN \right)}_{6}} \right]}^{4-}}$ > $P{{O}_{4}}^{3-}$ > $S{{O}_{4}}^{2-}$ > $C{{l}^{-}}$
(C) Arsenic sulphide sol : $N{{a}^{+}}>B{{a}^{2+}}>A{{l}^{3+}}$
     Ferric hydroxide sol : $C{{l}^{-}}>S{{O}_{4}}^{2-}>P{{O}_{4}}^{3-}>{{\left[ Fe{{\left( CN \right)}_{6}} \right]}^{4-}}$
(D) Arsenic sulphide sol : $C{{l}^{-}}>S{{O}_{4}}^{2-}>P{{O}_{4}}^{3-}>{{\left[ Fe{{\left( CN \right)}_{6}} \right]}^{4-}}$
     Ferric hydroxide sol : $N{{a}^{+}}>B{{a}^{2+}}>A{{l}^{3+}}$

Answer 1

Hint: Flocculating value or the coagulating value is the amount of the electrolyte which is needed so that 1 litre of colloidal solution precipitates easily. The coagulating power or flocculating power is the reciprocal of coagulating value or flocculating value.

Complete step by step solution:
-Colloidal solutions are those types of solutions which are formed when a substance is suspended in a fluid such that their solution is not clear and appears as a mixture. It is also called a colloidal suspension.
-Colloid is a very thin material which is present throughout the colloidal solution. It is very small and is uniformly spread in the mixture. When these colloids are made to clump together in order to precipitate themselves, the process is called flocculation.
-In the process of flocculation, the colloids can come out of their suspensions in two ways. They can either come out spontaneously or they come out with the help of an agent called as a clarifying agent which is added for this purpose only.
-Both the processes of coagulation, as well as flocculation, are very important for the treatment of water as they destabilize the suspensions chemically making the water pure. Coagulation destabilizes the particles while flocculation carries the particles away from the water.
-The chemical reaction involved in the process can be shown as
$A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}.14{{H}_{2}}O\to 2Al{{\left( OH \right)}_{3}}\left( s \right)+6{{H}^{+}}+3S{{O}_{4}}^{2-}+8{{H}_{2}}O$
-Colloids interact with the ions which have a charge that is opposite to the charge present on the colloids themselves. This is because the unlike charges have the tendency to attract each other resulting in neutralization of the reaction leading to increased stability with the release of energy.
-The flocculating power of an ion is directly proportional to its charge present. It means that the flocculating power is more for an ion having greater valency. More the valency of an ion more is the power of the ion to cause precipitation of the colloids. This is called Hardy-Schulze rule.
-So, negative sols will be precipitated by positive ions called cations and positive sols will be precipitated by negative ions called anions and their order will increase with their charges.

Thus the correct option is B.

Note: The ions which neutralize the charge of the colloidal solutions causing them to precipitate is called coagulating ions. Blood is also purified with this method only. It is a negatively charged sol and is coagulated by positively charged ions.