Which of the following statement is incorrect?

Mixing two oppositely charged sols neutralizes their charges and stabilises the colloid.

The correct answer is option 3. Mixing two oppositely charged sols neutralizes their charges and stabilises the colloid.

Let us go through each statement in detail to fully understand which one is incorrect and why:

Statement 1: Brownian movement stabilizes sol.

Brownian movement refers to the random, continuous motion of colloidal particles when suspended in a fluid. This motion is caused by collisions between the colloidal particles and the molecules of the dispersion medium (e.g., water, air).

Stabilization of sol occurs because Brownian motion prevents the colloidal particles from settling due to gravity. As the particles move randomly, they remain dispersed throughout the medium. This motion also reduces the chances of particles aggregating (clumping together) and forming larger particles that could settle out.

Conclusion: This statement is correct because Brownian movement helps keep colloidal particles dispersed and prevents them from aggregating or settling, thus stabilizing the sol.

Statement 2: Both emulsifier and peptising agents stabilize colloids but their actions are different.

Emulsifiers are agents used to stabilize emulsions (colloidal systems where liquid droplets are dispersed in another liquid). They work by forming a protective layer around the dispersed droplets, preventing them from coalescing (merging together). This is common in oil-in-water or water-in-oil emulsions, like milk.

Peptizing agents are used to convert a precipitate back into a colloidal form, stabilizing it by breaking down particle aggregates into smaller colloidal particles. They do this by adsorbing onto the surface of the particles and imparting a charge, preventing the particles from clumping together.

Although both emulsifiers and peptizing agents stabilize colloids, they operate in different ways: one prevents the coalescence of droplets in emulsions, while the other prevents particle aggregation in sols.

Conclusion: This statement is correct because both stabilize colloids, but their actions differ depending on whether the system is an emulsion or a sol.

Statement 3: Mixing two oppositely charged sols neutralizes their charges and stabilizes the colloid.

When you mix two oppositely charged sols (e.g., a positively charged sol and a negatively charged sol), the charges on the particles neutralize each other. This often leads to coagulation or flocculation because the repulsive forces that normally keep the particles apart are reduced or eliminated.

Once the charges are neutralized, there’s no force preventing the particles from coming together. As a result, the colloidal particles aggregate (clump together), which often leads to the formation of larger particles or precipitates. Stabilization of colloids depends on the presence of charge (or steric factors) that keep the particles dispersed. Removing or neutralizing these charges typically destabilizes the colloid.

Conclusion: This statement is incorrect because neutralizing the charges by mixing two oppositely charged sols usually leads to aggregation and destabilization, not stabilization.

Statement 4:The stability of lyophobic colloidal particles is due to preferential adsorption of ions on their surface from the solution.

Lyophobic colloids (solvent-hating colloids) are inherently unstable in a dispersion medium like water because the dispersed particles do not have an affinity for the solvent. However, they can be stabilized by the adsorption of ions from the solution onto their surface

The adsorbed ions create a layer of charge around the colloidal particles, which generates a repulsive force between them. This prevents the particles from coming together (aggregating), thus stabilizing the colloid.

This preferential adsorption of ions leads to the formation of an electric double layer around each colloidal particle. The repulsion between these charged layers prevents the particles from clumping together.

Conclusion: This statement is correct because the stability of lyophobic colloids is due to the adsorption of ions, which creates electrostatic repulsion between particles, keeping them dispersed.

The incorrect statement is Statement 3: "Mixing two oppositely charged sols neutralizes their charges and stabilizes the colloid.