CHEMISTRY [3 Mark Question Answer]

Fractional distillation : The process of distillation is used for separating the components of a homogeneous liquid-liquid mixture, like water and alcohol. This is based on the fact that alcohol boils at a lower temperature than water. The vapour of alcohol are collected and cooled while water is left behind in the original vessel. Thus, two liquids having different boiling points can be separated by distillation provided that difference in their boiling points must be 25 °C or more.

By using a separating funnel : It is a simple device used to separate the components of a liquid-liquid heterogeneous mixture.
Example : Kerosene oil and water. The mixture is placed in a separating funnel and allowed to stand for sometime. The components form two clear layers. Water being heavier forms the lower layer and oil being lighter forms the upper layer. When the stopper of the funnel is opened, the heavier liquid trickles out slowly and is collected in a vessel. The stopper is closed when the bottom layer is entirely removed the funnel. In this way, the two liquids are separated

Solvent extraction method : This method is used when one of the solid components is soluble in a liquid.

Example : A mixture of sand and salt can be separated by this method. Salt gets dissolved in water while sand settles down in the container. The salt solution is then decanted. Salt is separated from the solution by evaporation. In this way, they can be separated.

Sedimentation and decantation : The settling down of suspended, insoluble, heavy, solid particles in a solid- liquid mixture when left undistrubed is called sedimentation.
The solid which settles at the bottom is called sediment while the clear liquid above it is called supernatant liquid.
The process of pouring out the clear liquid, without disturbing the sediment, is called decantation.
Example : A mixture of sand and water.

Filtration : The process of separating insoluble solid particles from a liquid by allowing it to pass through a filter is called Alteration. These filters allow liquids to pass through them but not solids. The insoluble solid left on the filter is called the residue, while the liquid which passes through the filter is called the filtrate. Mixtures like chalk and water, clay and water, tea and tea leaves, sawdust and water, etc., are separated by this method.

Advantages of chromatography :

(i) A very small quantity of the substance can be separated.

(ii) Components with very similar physical and chemical properties can be separated.

(iii) It identifies the different constituents of a mixture.

(iv) lt also helps in quantitative estimation of components of a mixture.

On heating the mixture, camphor will evaporates as it is a sublime substance. Its vapours can be collected which will solidify on cooling. Common salt and chalk powder mixture is then mixed in water. Common salt gets dissolved in water while chalk powder does not. Then by filtration, chalk powder is removed from the solution as it gets deposited in filter paper. The filtrate contains water and common salt. Common salt can be separated from water by evaporation process.

Pure substance : Pure substances have a definite set of properties such as boiling point, melting point, density, etc. They are all homogeneous i.e., their composition is uniform throughout the bulk. Both elements and compounds are pure substances.
Pure substances are needed to :

1. Manufacture medicines.
2. To prepare chemicals in industry.
3. For scientific purposes.
4. To maintain the good health of human beings.