Question

Which of the following is an example of associated colloid? (a) Protein in water (b) Soap in water (c) Rubber in benzene (d) \(\mathrm{FeCl}_{3}\) in \(\mathrm{H}_{2} \mathrm{O}\)

Short answer

Soap in water (b) is an example of an associated colloid.

Step-by-step solution

Understand Types of Colloids

Colloids are substances that are dispersed evenly throughout another substance. There are two types of colloids: lyophobic (solvent hating) and lyophilic (solvent loving). Understanding the types is essential before identifying which one is an associated colloid.

Define Associated Colloids

Associated colloids, also known as micelles, are formed when surfactant molecules at a certain concentration (called the critical micelle concentration) aggregate into larger colloidal-sized particles. Soap forms such colloids in water.

Identify the Associated Colloid

By comparing the options with the definition of associated colloids, we can determine that soap in water forms micelles and hence is an example of an associated colloid.

Key concepts

Colloids

Imagine mixing two substances together, but instead of fully combining like sugar in tea, they form a sort of 'mini-mixture' where tiny particles of one substance float around within the other. That's what we call a colloid. In the kitchen, mayonnaise is a common example, where oil particles are dispersed in water. But it's not just about food; colloids are all around us, from fog to paint.

In the context of our problem, colloids involve one substance (commonly known as the dispersed phase) being distributed evenly within another substance (the continuous phase). The size of these particles is crucial; they're bigger than those in a solution, but small enough not to settle out under gravity. Because of the colloids' stability, they don't separate easily, which is why fog doesn't just 'split' back into water and air.

Critical Micelle Concentration

Ever wondered why detergents clean better when you use just the right amount? That's where the critical micelle concentration (CMC) comes in. CMC is a bit like the 'Goldilocks zone' for soapy water. Below this concentration, the soap molecules simply float around solo, but when you reach this magic number, they start gathering into tiny clusters called micelles.

In our exercise, we're focusing on surfactant molecules, which have a unique talent: one end loves water (hydrophilic) and the other hates it (hydrophobic). At the CMC, these molecules assemble with their hydrophobic tails inwards and their hydrophilic heads outwards. This assembly forms micelles, which can trap oils and dirts inside, allowing them to be rinsed away with water. It's fascinating because this process turns a bunch of single surfactant molecules into a sophisticated team that's really good at cleaning.

Surfactant Molecules

Surfactant molecules are like the Swiss Army knives of the molecular world. They are active substances that drastically reduce the surface tension of liquids. Because they're ambidextrous with water — one side adores it, and the other side avoids it — they make things like detergents, shampoos, and emulsifiers incredibly effective.

In our exercise, surfactant molecules are the reason why soap becomes an associated colloid in water. When you reach the critical micelle concentration, these molecules stop being loners and start forming groups, with tails tucked away from the water, creating a shielded environment. Think of it as a micro-tactic to tackle grime: inside the micelle, all things oily and dirty are captured, and the outer water-loving parts make sure the whole package is washable. Thanks to these tiny chemistry heroes, we can remove unwanted substances from various surfaces and enjoy the feeling of cleanliness.