Separation of Components of a Mixture

Is matter pure??

For a common man, purity means that there is no adulteration in the matter.
But for scientists, purity means that all the constituent particles of that substance are same in their chemical nature.

Example: It is written "pure" on milk packs. Here, pure means no adulteration is done, but milk itself is a mixture of fats, proteins, water, etc. Hence, a chemist doesn't consider milk as pure.

*image taken from google.

For a chemist, it is necessary to separate components of a mixture. The separation of the components makes it possible to study and use the individual components of a mixture.

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In a mixture, solute and solvent can exist in following pairs:
1. Solid-solid
2. Solid-liquid
3. Liquid-liquid
4. Gas-gas
(Though we have more combinations, but the separation techniques that we use comprises mainly of these pairs)

Solid-Solid

Hand picking: Use to separate heterogeneous mixture by simple physical method.

Threshing: Generally use to separate grain seeds from their stalks.
Winnowing: use to separate heavier and lighter components by wind or blowing air.
Sieving: use to separate fine particles from bigger particles of a mixture by passing through a sieve.
Sublimation: Use to separate the mixture in which 1 of the components can sublimate.
Magnetic separation: Used to separate the mixture in which 1 of the components is of magnetic nature like iron filings.

Solid-liquid

Crystallisation: A supersaturated solution is allowed to cool down and crystals of pure solid separates out.
Evaporation: Use to separate the volatile component (solvent) from its non-volatile solute.
Sedimentation and decantation: In this, heavier components settle after water is added and then water along with lighter impurities is poured into another container.
Filtration: Components of size greater than 100 nm cannot pass through filter paper and hence can be separated using filter papers.
Chromatography: Used for separation of those solutes that dissolve in the same solvent.
Churning (or centrifugation): In this, the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

Liquid-liquid

Distillation: Use for separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.
Fractional distillation: Temperature difference between 2 miscible liquids is less than 25 K.
Using separating funnel: The immiscible liquids separate out in layers depending on their densities.

Gas-gas

Separation of components of air: Consecutive freezing and fractional distillation is done.

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When more than 2 components are present, a combination of various techniques can be used. For example, for separating a mixture of ammonium chloride, salt and sand, we can first heat the mixture in China dish, ammonium chloride will sublimate and get separated. Next, add water to the mixture of sand and salt. Salt will dissolve and sand remain as it is. Filter the sand. Now, you are left with only salt solution. Evaporate water and you will get salt crystals. Hence, all the components of a mixture are separated.

Mixtures

The matter, we see around us, can be classified into 2 categories:
1. Pure substance
2. Mixture.

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Pure Substance

A pure substance consists of a single type of particles. Hence, it cannot be separated into other kinds of matter by any physical process.

Mixture

Mixtures are constituted by more than one kind of pure form of matter.The constituents are mixed in any proportion. Hence, mixtures has no chemical formula.

Example: Sugar can be separated from a sugar solution via evaporation. However, sugar itself is a substance which cannot be separated into its chemical constituents by physical process.

Depending upon the composition of the constituents, we can have 2 types of mixtures.
Homogeneous: solute and solvent together form 1 phase and no physical boundary is visible.
Heterogeneous: solute and solvent forms distinct phase and can be distinguished easily.

Characteristics of Mixtures

The characteristics of mixtures are given below:

1. Mixture has no fixed composition.
2. Energy is neither produced nor evolved while forming a mixture.
3. Mixture has no fixed melting point and boiling points.
4. Mixture retain the properties of its components.
5. Components of mixtures can be separated by simple physical methods.

Types of Mixtures

Solution
A solution is a homogeneous mixture of two or more substances. For example, lemonade, soda water, alloys, air, etc.

Colloid
Colloid is a heterogeneous mixture of two or more substances. Due to the relatively smaller size of particles, as compared to suspension, the mixture appears to be homogeneous. For example, milk, fog, jelly, etc.
We cannot see colloidal particles but these particles scatter light. This scattering of light is called the Tyndall effect.

Suspension
A suspension is a heterogeneous mixture in which the solute particles do no dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension are visible to the naked eyes.

Purity of Matter:
Matter around us is not pure. There us various techniques which are used to separate the components of mixtures like, hand picking, winnowing, centrifugation, distillation, chromatography, etc.