Question

Which of the following ions has the least flocculation value?

• A. ${\mathrm{Cl}}^{-}$
• B. ${\mathrm{SO}}_4^{2-}$
• C. ${\mathrm{PO}}_4^{3-}$
• D. $[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6{]}^{4-}$

Answer 1

The correct option is A

${\mathrm{Cl}}^{-}$

Explanation for the correct option:

A. ${\mathrm{Cl}}^{-}$

• The flocculation value is the minimum amount of electrolyte added to cause the coagulation (precipitation) of the colloidal solution.
• The flocculation value is directly proportional to the charge of the ion. Thus, the greater the charge of the ion, the more is the flocculation value.
• Of the given ions, the Chloride ion (${\mathrm{Cl}}^{-}$) has the least charge of $-1$, thus it has the least flocculation value.

The explanation for the incorrect options:

B. Sulphate ion (${\mathrm{SO}}_4^{2-}$) has $-2$ charge which is greater than the charge of ${\mathrm{Cl}}^{-}$.

C. Phosphate ion (${\mathrm{PO}}_4^{3-}$) has $-3$ charge which is greater than the charge of ${\mathrm{Cl}}^{-}$.

D. $[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6{]}^{4-}$ has $-4$ charge which is greater than the charge of ${\mathrm{Cl}}^{-}$.

Hence, the correct option is A, ${\mathrm{Cl}}^{-}$.