Question

Which of the following has minimum flocculation value?
(A) $P{b^{2 + }}$
(B) $P{b^{4 + }}$
(C) $S{r^{2 + }}$
(D) $N{a^ + }$

Answer 1

Flocculation value shows power of any ion to flocculate any sol particles from its solution. We can use the Hardy-Schulze rule to get an idea about the flocculation value of any ion.

Complete step by step answer:
If we take 1 litre of colloidal solution, then the number of millimoles of active ions required to bring flocculation in the solution is called flocculation value if any ion.
According to Hardy-Schulze rule, higher the valency of the ion, higher will be its coagulation power.
We have four ions given in the options.
$P{b^{4 + }}$ has valency +4, $P{b^{2 + }}$ has valency +2, $S{r^{2 + }}$ has valency +2 and $N{a^ + }$ has valency +1.
Out of them, $P{b^{4 + }}$ has the highest valency which is +4. So, according to the Hardy-Schulze rule, we can say that $P{b^{4 + }}$ will have the highest flocculation value from given options.
So, the correct answer is “Option B”.

Additional Information:
To coagulate or flocculate a sol, one method is to add electrolyte into in and hence, depending upon the type of the sol, either cations or anions depending upon their respective coagulation power, can do flocculation of sol.
So, the different electrolytes have different coagulating properties.
Ions that are carrying opposite charge than that of the sol particles, are eligible to cause flocculation.

Note: Remember that if anions are given in the options then there is the same rule for them also. The rule does not change for anions and cations. Do not get confused between flocculation and precipitation of salt as they are both different phenomenons.