A highly positively charged ferric hydroxide sol is independently coagulated by three electrolytes: — Surface Chemistry Chemistry Question
Question
A highly positively charged ferric hydroxide sol is independently coagulated by three electrolytes: $Na_2SO_4$, $K_3[Fe(CN)_6]$, and $NaCl$. The effective active anions are $SO_4^{2-}$, $[Fe(CN)_6]^{3-}$, and $Cl^-$. If we assume the empirical model where the absolute coagulating power is strictly proportional to the fourth power of the valency of the active ion ($Valency^4$), how many times more powerful is the $[Fe(CN)_6]^{3-}$ ion compared strictly to the $Cl^-$ ion?
💡 Solution & Explanation
For a positively charged sol, the active coagulating ions are the anions. Their valencies are $3$ for $[Fe(CN)_6]^{3-}$ and $1$ for $Cl^-$. According to the given 4th power model: $\text{Ratio} = \frac{3^4}{1^4} = \frac{81}{1} = 81$. The complex ion is 81 times more powerful.