Problem 168 - A Complete Resource Book in Chemistry for JEE Main

Question

$$ \begin{aligned} &\text { Match the following }\\\ &\begin{array}{ll} \hline \text { Column-I } & \text { Column-II } \\ \hline \text { (a) Protective colloid } & \text { (p) } \mathrm{FeCl}_{3}+\mathrm{NaOH} \\ \text { (b) Liquid - liquid colloid } & \text { (q) Lyophilic colloids } \\ \text { (c) Positively charged } & \text { (r) Emulsion } \\ \text { colloid } & \\ \begin{array}{c} \text { (d) } \text { Negatively charged } \\ \text { colloid } \end{array} & \text { (s) } \mathrm{FeCl}_{3} \text { hot water } \\ \hline \end{array} \end{aligned} $$

Step-by-Step Solution

Answer

(a) - (q), (b) - (r), (c) - (p), (d) - (s).

Step 1: Understanding the Terms

Review the terms given in Column-I: protective colloid, liquid-liquid colloid, positively charged colloid, and negatively charged colloid. Look at Column-II: FeCl3 + NaOH, Lyophilic colloids, Emulsion, FeCl3 hot water.

Step 2: Matching Protective Colloid

A protective colloid is a substance that stabilizes a colloidal system and prevents the particles from grouping together. This corresponds to 'Lyophilic colloids', which are solvent-attracting substances that have a protective action on lyophobic (solvent-repelling) colloids. Match (a) with (q).

Step 3: Matching Liquid-Liquid Colloid

A liquid-liquid colloid is commonly known as an emulsion, which is a mixture of two immiscible liquids. Match (b) with (r) indicating 'Emulsion'.

Step 4: Matching Positively Charged Colloid

A positively charged colloid refers to a colloid where the dispersed particles carry a positive charge. FeCl3 with NaOH produces a positive sol. Match (c) with (p) representing the reaction 'FeCl3 + NaOH'.

Step 5: Matching Negatively Charged Colloid

A negatively charged colloid contains particles with a negative charge. The dispersion of FeCl3 in hot water often forms a negative sol. Match (d) with (s) indicating 'FeCl3 hot water'.

Key Concepts

Protective colloids

Protective colloids play a crucial role in stabilizing colloidal systems. They act as shields to prevent the tiny dispersed particles within colloids from coming together and clumping. This is particularly important in maintaining the structure and function of various colloids in industries such as pharmaceuticals or food production.

A protective colloid works by increasing the viscosity of the medium and creating a barrier around the particles. This is often achieved using substances known as lyophilic colloids. Lyophilic colloids are characterized by their strong affinity for the solvent, which helps them surround and stabilize lyophobic (solvent-repelling) colloid particles.

Some practical applications of protective colloids include:

• Improving longevity and stability in paints and inks, ensuring they remain uniform and effective upon application.
• Used in food production to improve texture and shelf-life of products like emulsions in mayonnaise.

These protective agents essentially prevent particles in colloidal suspensions from aggregating and settling, ensuring they remain evenly distributed throughout the medium.

Emulsions

Emulsions are mixtures where two immiscible liquids, such as oil and water, are combined. They are stabilised by emulsifying agents that help maintain the mixture without separating. This is crucial in many everyday products, from foods to cosmetics, where texture and appearance matter.

Think of emulsions as stable mixes where tiny droplets of one liquid are dispersed into another. Without an emulsifying agent, these droplets would quickly coalesce and separate.

• A common example is mayonnaise, an emulsion of oil in water, stabilized with egg yolk as the emulsifying agent.
• In cosmetics, lotions are emulsions with oils dispersed within water, giving them a consistent creamy texture.

Understanding emulsions helps in choosing the right substances to ensure stability in products like these, preventing them from separating and ensuring their effectiveness and longevity.

Positively charged colloids

Colloids consist of small particles dispersed in a medium. Sometimes, these particles are charged, and positively charged colloids have dispersed particles with a positive electrical charge. This charge is crucial as it influences how particles interact with each other and can affect the properties and behavior of the colloid.

In chemistry, reactions between substances like ferric chloride (FeCl₃) and sodium hydroxide (NaOH) can result in the formation of positively charged sols. The surplus of positive ions in these systems leads to positively charged colloids.

• Positively charged colloids often attract negatively charged ions in the solution, leading to a more stable arrangement of particles.
• They are used in water purification processes to coagulate and separate impurities.

Understanding positively charged colloids is essential, especially in fields like environmental science and chemical engineering, where they are applied to manage waste treatment processes efficiently.

Negatively charged colloids

Just like their positively charged counterparts, negatively charged colloids have dispersed particles that carry a negative charge. This characteristic is pivotal in determining how these colloids interact and react with other substances in their environment.

A frequent example of negatively charged colloids is the dispersion created when ferric chloride (FeCl₃) is introduced to hot water, resulting in a sol containing negatively charged particles.

• These colloids attract positive ions, helping stabilize the colloid and maintain an even distribution of particles.
• This charge helps in applications such as clay water suspensions that, due to their negative charge, prevent the clay particles from getting too close and linking up.

By understanding negatively charged colloids, we can better comprehend and manipulate the stability of colloidal systems, which is valuable in industries such as coatings, pharmaceuticals, and environmental management.