Separation of Mixtures is very important to obtain the desired component. Different techniques are used to separate different mixtures that are discussed below.Please read the first part of this chapter first ➡ Chapter - Matter related to class 7 chemistry chapters ICSC
How to separate solid-solid mixture?
What is sublimation?
It is a process in which the solid directly changes into gas on heating without changing into liquid. Some examples of sublime products are camphor, benzoic acid, ammonium chloride, dry ice, naphthalene balls etc.
∆
Solid ➡ Gas
∆
Camphor ➡ Camphor Vapours
What is the principle of sublimation?
The principle of sublimation is applied for separating a mixture that consists of the constituents that sublime on heating.
What is the technique used in sublimation?
When the mixture is heated, the product that sublimes changes into vapours.The solid is obtained back by cooling down the vapours.The product that doesn't sublime remains in the dish.
How to separate solid-liquid mixture?
What is evaporation?
The process by which a liquid is changed into its gaseous state below its boiling point is known as evaporation.
What is the principle of evaporation?
When a solid-liquid mixture is heated, the liquid is evaporated and the solid portion is left behind.
What is the technique used in evaporation?
The liquid in the solid-liquid mixture gets evaporated on heating or exposing to sunlight while the solid part is left behind. For example - common salt and water.
What is distillation?
The process in which the liquid is separated by heating the solid-liquid mixture and then changing it into its vapours and then its vapours are cooled down to obtain the liquid back.It is also used to separate miscible liquids if the difference in their boiling points is more than 25°C.
What is the principle used in distillation?
The method is used to obtain both solid and liquid from the mixture.
What is the technique used in distillation?
Upon heating a homogenous mixture of solid and liquid in a distillation flask, the liquid forms vapours.These vapours cool down and change back into pure liquid on passing through the condenser. This pure liquid is collected in a separate flask and is known as distillate. The solid constituent is left behind in the distillation flask. For example - Distilled or pure water can be obtained by the process of distillation.
How to separate liquid-liquid mixture?
There are two types of mixtures -
(a) Miscible liquids - These are the liquids that mix with each other and form a single layer. For example - juice and water, milk and water etc.
(b) Immiscible liquids - These are the liquids that do not mix with each other and form a separate layer. For example - oil and water.
What is fractional distillation?
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| Fractional Distillation |
This method is used to separate the mixture that consists of miscible liquids having different boiling points. The difference in boiling points of liquids should be less than 25°C.
For example - A mixture of acetone and methanol is separated by this method. The boiling point of acetone is 56°C and methanol is 65°C.So acetone boils first. Its vapours start rising in the fractionating column and then move to the condenser where they are condensed and changed into liquid form which is collected in the receiver.
How is the mixture of immiscible liquids separated ?
The mixture of immiscible liquids is separated using a separating funnel.
For example -The mixture of oil and water that is taken in the separating funnel form two separate layers. The upper layer consists of oil while the lower layer consists of water. On opening the stopper, the heavier liquid i.e water flows down first and collects in a container. The stopper is closed after it is completely transferred. The lighter liquid i.e oil remains in the separating funnel. This method is used to separate immiscible liquids such as petrol and water, oil and water, and carbon tetrachloride and water.
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