Subject: Chemistry
Class: SS 1
Curriculum: Standard
In chemistry, we rarely find substances in their pure states. Most matter around us exists as mixtures. To study these substances or use them in industries, we must isolate them. Separation techniques are physical methods used to divide a mixture into its individual components. These techniques do not change the chemical identity of the substances; instead, they exploit differences in their physical properties, such as boiling point, density, particle size, solubility, and magnetism.
Sieving is a method used to separate solid mixtures containing particles of different sizes. The mixture is placed on a mesh (sieve) and shaken. Particles smaller than the mesh openings pass through, while larger particles are retained on top.
This technique is used to separate magnetic substances from non-magnetic ones. When a magnet is brought close to the mixture, the magnetic components are attracted and cling to the magnet, leaving the non-magnetic materials behind.
Sedimentation is the process by which heavy, insoluble solid particles suspended in a liquid settle to the bottom of the container over time due to gravity. The clear liquid on top (the supernatant) can then be carefully poured off into another container without disturbing the sediment—a process called decantation.
Evaporation is used to recover a soluble solid solute from its liquid solvent. The solution is heated until the liquid boils and turns into vapor, leaving the solid residue behind in the evaporating dish.
Distillation is a process that involves vaporizing a liquid and then condensing the vapor back into a liquid (distillate) in a separate container.
Simple Distillation separates a pure solvent from a solution (e.g., pure water from salty water).
Fractional Distillation separates two or more miscible liquids with close but distinct boiling points (e.g., ethanol and water) using a fractionating column.
Physical Property Exploited: Differences in boiling points.
Practical Example: Producing distilled water for laboratory experiments.
A separating funnel is used to separate two or more immiscible (unmixable) liquids. When the mixture is poured into the funnel and allowed to stand, it forms distinct layers based on density. The denser liquid settles at the bottom and is carefully drained out by opening the tap, leaving the less dense liquid inside the funnel.
In industrial and environmental engineering, multiple separation techniques are often combined. For instance, municipal water treatment plants cannot rely on a single step to purify drinking water. They first use sedimentation in large basins to remove heavy mud, followed by filtration (a advanced form of sieving) to trap smaller dirt particles, before chemical disinfection.
Similarly, the mining industry relies heavily on magnetic separation and sieving to process raw ores before chemical extraction begins. Understanding these physical properties allows engineers to design large-scale systems that keep our environment clean and provide raw materials for manufacturing.
In the global petroleum industry, fractional distillation is used to separate crude oil into highly valuable fractions like petrol, diesel, and kerosene.
Home-Practice Activity: To observe density separation at home, shake a mixture of cooking oil and water in a clear plastic bottle, let it stand for five minutes to watch the distinct layers form, and then carefully pour the top oil layer into another cup.