How Everyday Mixtures Are Separated in Real Life

Mixtures are separated using different methods based on the properties of their components, such as size, solubility, magnetism, or boiling point. In ICSE Class 6 Chemistry, you learn to use handpicking, winnowing, sieving, magnetic separation, sublimation, sedimentation, decantation, filtration, evaporation, crystallisation, distillation, and separating funnels. This article covers all these methods with examples and explains which property is used for each, as required for Class 6 Chemistry (ICSE).

Solid-solid mixtures can be separated by handpicking, winnowing, sieving, magnetic separation, and sublimation, depending on the differences in size, weight, magnetic property, or ability to sublime. Handpicking is used when the components are large enough to be picked by hand, such as removing stones from rice. Winnowing separates lighter particles from heavier ones using wind or air; for example, separating husk from wheat grains. Sieving uses a sieve with holes of a specific size to separate larger particles from smaller ones, like separating sand from gravel. Magnetic separation is used when one component is magnetic, such as removing iron filings from a mixture with sand. Sublimation separates substances that change directly from solid to gas on heating, like separating ammonium chloride from salt. For example, in real life, winnowing is commonly seen when farmers use wind to separate chaff from grains after harvesting. A common misconception is that these methods work for all mixtures, but each only works when the property difference is clear.

To separate an insoluble solid from a liquid, you can use sedimentation and decantation, loading, or filtration. Sedimentation allows the heavier solid particles to settle at the bottom of a container, forming a sediment. Decantation is pouring off the clear liquid from above the sediment. Loading is the process of adding a substance (like alum) to make fine particles settle faster. Filtration uses a filter paper and funnel to separate insoluble solids from liquids. For example, in real life, muddy water is first allowed to settle (sedimentation), then the clear water is poured off (decantation). In kitchens, tea leaves are separated from tea using a sieve or filter (filtration). The apparatus used for filtration is a filter paper placed in a funnel. Some students think all solids can be filtered, but only insoluble ones can be separated this way.

A soluble solid can be recovered from its solution by evaporation or crystallisation. Evaporation involves heating the solution so the liquid evaporates, leaving the solid behind. Crystallisation is a process where the solution is heated to remove some water, then cooled to form pure crystals of the dissolved solid. Crystallisation is preferred when the solid decomposes on strong heating, as it is a gentler method. For example, common salt is obtained from seawater by evaporation. In sugar factories, crystallisation is used to get pure sugar crystals from sugar solution. Students often think evaporation always gives pure solids, but crystallisation gives purer crystals when the solid is heat-sensitive.

Liquid mixtures are separated by simple distillation, fractional distillation, or using a separating funnel, depending on whether the liquids are miscible or immiscible. Simple distillation separates a liquid from a solution or two miscible liquids with different boiling points, by heating the mixture and condensing the vapour. Fractional distillation is used for miscible liquids with closer boiling points, using a fractionating column to improve separation. Separating funnels are used for immiscible liquids, which form separate layers; the denser liquid is drained off from the bottom. For example, in real life, separating oil from water uses a separating funnel. Distillation is used in laboratories to purify water. A common error is trying to use a separating funnel for miscible liquids, which will not work.