Animated Solution for Chemistry - Surface Chemistry: Among the following, the false statement is

Welcome to the fascinating realm of surface chemistry! Today, we are embarking on a mission to evaluate four intriguing statements about colloids. Our goal is to act as scientific detectives and identify the single false statement hidden among them.

Let's begin our investigation with the first statement, which claims that the Tyndall effect can distinguish between a colloidal solution and a true solution.

To understand this, we must zoom in to the microscopic level. In a true solution, the dissolved particles are incredibly tiny, typically measuring less than $1\text{ nm}$ in diameter.

Because these particles are so minuscule, they are completely invisible to passing light waves. The light simply passes through without any interference.

However, a colloidal solution is a different story entirely. The particles here are much larger, ranging from $1\text{ nm}$ to $1000\text{ nm}$.

When a beam of light travels through a colloid, these larger particles act as obstacles. They scatter the light in all directions, making the path of the beam brilliantly visible.

This phenomenon is known as the Tyndall effect. Therefore, the first statement is a perfectly accurate scientific fact.

Next, we turn our attention to the skies. The second statement suggests that we can cause artificial rain by throwing electrified sand from an airplane.

At first glance, this might sound like science fiction, but it is grounded in solid electrostatic principles. Clouds are not just floating water; they are massive colloidal aerosols.

The water droplets suspended in the air carry a uniform electric charge. Because like charges repel, these droplets constantly push away from each other, preventing them from merging.

This electrostatic repulsion is the exact reason why clouds can float for days without raining.

If we introduce sand carrying an opposite electric charge into this system, a dramatic neutralization occurs. The oppositely charged sand particles attract the cloud droplets, neutralizing their charge.

Without the repulsive force keeping them apart, the droplets rapidly collide and merge. They coagulate into heavy drops that gravity finally pulls down as rain.

Thus, the second statement is also completely true.

Our third statement brings us to the stability of lyophilic sols. It claims that these liquid-loving colloids can be coagulated by adding an electrolyte.

Lyophilic sols are famous for their incredible stability. Their particles are heavily solvated, meaning they are wrapped in a thick, protective blanket of solvent molecules.

This hydration sphere acts as a physical barrier, preventing the colloidal particles from coming close enough to stick together.

However, they are not entirely invincible. If we introduce a massive amount of an electrolyte into the system, a fierce competition begins.

The ions from the electrolyte aggressively attract the solvent molecules, effectively stripping the protective blanket away from the colloidal particles.

This process is known as salting out. Once the protective layer is gone, the bare colloidal particles collide and coagulate.

Therefore, the third statement holds true under the right conditions.

Finally, we arrive at the fourth statement. It boldly claims that latex is a colloidal solution of rubber particles which are positively charged.

Let's visualize the physical reality of latex. Natural latex is a milky sap extracted from rubber trees.

It is a highly stable emulsion consisting of polymer microparticles—specifically polyisoprene rubber—suspended in an aqueous medium.

But what about their electrical charge? This is where the statement makes a fatal error.

In natural latex, the rubber microparticles are enveloped by a layer of proteins and phospholipids. At the natural pH of the sap, these biological molecules ionize.

This ionization imparts a strong, net negative charge to the surface of the rubber particles.

The statement explicitly claims they are positively charged, which is a direct contradiction of the physical facts.

Our investigation is complete. We have carefully analyzed the physics and chemistry behind each option.

We confirmed the reality of the Tyndall effect, the mechanism of artificial rain, and the coagulation of lyophilic sols.

However, the claim about latex carrying a positive charge is factually incorrect.

Therefore, the false statement we were hunting for is indeed the fourth one. Option (d) is our final answer.