For the coagulation of a negative sol, the species below, that has the highest flocculating power is

Q: What exactly is a negative sol?

A negative sol is a colloidal solution where the dispersed particles carry a net negative electrical charge on their surface. This charge prevents them from coming together due to electrostatic repulsion.

Q: Why do we need cations to coagulate a negative sol?

Coagulation happens when the repulsive forces between colloidal particles are neutralized. Since the sol is negative, we need positively charged ions (cations) to neutralize the surface charge and allow the particles to clump together.

Q: What is the Hardy-Schulze law?

The Hardy-Schulze law states that the coagulating (or flocculating) power of an ion is directly proportional to its valency. An ion with a higher charge is much more effective at causing precipitation.

Q: What is the difference between coagulation value and flocculating power?

They are inversely related. Coagulation value is the minimum concentration of an electrolyte required to cause coagulation. Flocculating power is the ability of an ion to cause coagulation. A highly powerful ion will have a very low coagulation value.

Q: Why are the sulfate and phosphate ions ineffective here?

Sulfate ($\text{SO}_4^{2-}$) and phosphate ($\text{PO}_4^{3-}$) are anions (negatively charged). Since the sol is already negatively charged, these ions will be repelled by the colloidal particles and will not cause coagulation.

Question

For the coagulation of a negative sol, the species below, that has the highest flocculating power is

Options:

(A) $	ext{SO}_4^{2-}$

(B) $	ext{Ba}^{2+}$

(C) $	ext{Na}^+$

(D) $	ext{PO}_4^{3-}$

Sigma Percentile · Accepted Answer

### The Mystery of the Negative Sol

Imagine you have a colloidal solution, specifically a **negative sol**. The particles in this sol are happily floating around, repelling each other because they all carry a negative charge. This electrostatic repulsion is what keeps the sol stable.

But what if we want to bring these particles together? What if we want them to clump up and settle down—a process we call **coagulation** or **flocculation**?

To do this, we need to neutralize their negative charges. And how do we neutralize a negative charge? By introducing a positive charge, of course! Therefore, to coagulate a negative sol, we need **cations** (positively charged ions).

### Filtering the Suspects

Let's look at the options provided in the question:
- $	ext{SO}_4^{2-}$ (Sulfate ion)
- $	ext{Ba}^{2+}$ (Barium ion)
- $	ext{Na}^+$ (Sodium ion)
- $	ext{PO}_4^{3-}$ (Phosphate ion)

Right off the bat, we can eliminate the anions. The sulfate ($	ext{SO}_4^{2-}$) and phosphate ($	ext{PO}_4^{3-}$) ions carry negative charges. If we add them to a negative sol, they will just be repelled by the colloidal particles. They are completely useless for our goal.

This leaves us with two candidates: the sodium ion ($	ext{Na}^+$) and the barium ion ($	ext{Ba}^{2+}$). Both are cations, so both can cause coagulation. But the question asks for the one with the **highest flocculating power**.

### The Hardy-Schulze Law

To determine which cation is the champion of coagulation, we turn to the **Hardy-Schulze Law**. This fundamental rule of surface chemistry states:

> **The greater the valency of the flocculating ion added, the greater is its power to cause precipitation.**

In simple terms, an ion with a higher charge packs a bigger punch. It can neutralize more colloidal particles per ion, making it much more efficient at causing coagulation.

### Crowning the Champion

Now, let's compare our two remaining candidates based on the Hardy-Schulze Law:
- The sodium ion ($	ext{Na}^+$) has a valency of $+1$.
- The barium ion ($	ext{Ba}^{2+}$) has a valency of $+2$.

Since $+2 > +1$, the barium ion has a significantly higher valency than the sodium ion. Therefore, according to the Hardy-Schulze Law, $	ext{Ba}^{2+}$ has a much higher flocculating power.

It will take far fewer barium ions to coagulate the sol compared to sodium ions. Thus, $	ext{Ba}^{2+}$ is the correct answer!

Animated Solution for Chemistry - Surface Chemistry: For the coagulation of a negative sol, the species below, that has the highest flocculating power is

Select Answer:

Visualized Solution

$Identifying the Sol$

$Filtering the Options$

$Hardy-Schulze Law$

$Comparing Valencies$

$Final Conclusion$

The Sigma Insight: Colloids, Micelles and and Emulsions

The Mystery of the Negative Sol

Filtering the Suspects

The Hardy-Schulze Law

Crowning the Champion

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