Answer the question on the basis of passage given below:
Adsorption is a surface phenomenon which can be expressed by means of an empirical relationship known as Freundlich Adsorption isotherm. The relationship is given by
\(\frac{x}{m} = Kp^{\frac{1}{n}}\left(n > 1\right)\)
\(x = \) Mass of the gas adsorbed
\(m = \) Mass of adsorbent
\(p = \) Pressure at which adsorption takes place
\(K\) and \(n\) are constant
Which electrolyte/ electrolytes can coagulate a ferric hydroxide sol most effectively?
A. K3[Fe(CN)6]
B. Na3PO4
C. Na2SO4
D. KNO2
E. KI
Choose the correct answer from the options given below
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A and B only
A ferric hydroxide sol is positively charged, so it is coagulated by anions. By the Hardy–Schulze rule, the greater the charge on the coagulating ion, the greater its coagulating power.
A. K3[Fe(CN)6] — Correct. It gives the ferricyanide ion \( \ce{[Fe(CN)6]^3-} \), charge 3−. Like the 4− ferrocyanide ion, the 3− ion of item A is highly charged, equal to \( \ce{PO4^3-} \).
B. Na3PO4 — Correct. It gives \( \ce{PO4^3-} \), charge 3−, the highest charge among the anions here with item A.
C. Na2SO4 — Incorrect. \( \ce{SO4^2-} \) carries a 2− charge, so it coagulates less effectively than the trivalent anions.
D. KNO2 — Incorrect. \( \ce{NO2^-} \) is univalent, a weak coagulant.
E. KI — Incorrect. \( \ce{I^-} \) is univalent, a weak coagulant.
NCERT (Pre-rationalised edition, 2022-23):
Coagulation or Precipitation – …
