Arrange the following electrolytes in the increasing order of van't Hoff factor(i) for complete dissociation of solute.
(A) \( [Co(NH_3)_6]Cl_3 \)
(B) \( MgCl_2 \)
(C) \( K_4[Fe(CN)_6] \)
(D) \( KCl \)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (D), (B), (A), (C)
The van’t Hoff factor i is the number of particles one formula unit gives in solution. For complete dissociation, i equals the number of ions formed. In a coordination compound the complex ion stays intact: only the ions outside the square bracket separate.
(A) \( \ce{[Co(NH3)6]Cl3 -> [Co(NH3)6]^3+ + 3Cl-} \): 1 + 3 = 4 ions, so i = 4.
(B) \( \ce{MgCl2 -> Mg^2+ + 2Cl-} \): 1 + 2 = 3 ions, so i = 3.
(C) \( \ce{K4[Fe(CN)6] -> 4K+ + [Fe(CN)6]^4-} \): 4 + 1 = 5 ions, so i = 5.
(D) \( \ce{KCl -> K+ + Cl-} \): 1 + 1 = 2 ions, so i = 2.
Shortcut: KCl gives the fewest ions and \( \ce{K4[Fe(CN)6]} \) the most, so the order starts with (D) and ends with (C): Options (2) and (3). \( \ce{MgCl2} \) (3 ions) comes before \( \ce{[Co(NH3)6]Cl3} \) (4 ions), which leaves Option (2).