Case Study Questions for Class 9 Science Chapter 5 Exploring Mixtures and their Separation (Exploration Book) 2026-27

Solutions, suspensions, and colloids differ primarily in the size of their particles. In a true solution, the solute particles are extremely small (less than 1 nm in diameter). Suspensions have much larger particles (more than 1000 nm in diameter) that eventually settle down when left undisturbed. Between these two lies another category of mixtures known as colloids. In a colloid, the particles range from 1 to 1000 nm in diameter. Unlike suspensions, colloidal particles do not settle over time from the mixture and remain uniformly dispersed.

When a fine beam of light is passed through a true solution, its path is not visible. However, when the same beam passes through a colloid, the particles are large enough to scatter the light, making the path of the beam clearly visible. The components of a colloid are specifically referred to as the dispersed phase and the dispersion medium.

When two liquids mix uniformly to form a single layer, they are called miscible liquids. A homogeneous mixture of two miscible liquids can often be separated by a process called distillation. This method involves heating the mixture until the liquid with the lower boiling point vaporises. The vapour is then directed through a condenser, where it is cooled and turned back into a pure liquid.

Simple distillation is effective when the boiling points of the two liquids differ by at least 25°C. For example, a mixture of acetone (boiling point 56°C) and water (boiling point 100°C) can be separated this way. However, if the boiling points of the liquids in the mixture differ by less than 25°C, a more complex process called fractional distillation must be used. This technique is extensively applied in petroleum refineries to separate crude oil into various useful fractions like petrol, diesel, and kerosene.