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.

---

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.

---

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.

Characteristics of Matter

We have already introduced matter. Matter is anything which has mass and occupy space. We can perceive matter from our 5 sensory organs, i.e., eyes, ears, tongue, nose and skin.

Now, let us discuss about the characteristics of this matter. 

1. Matter is made up of particles.
Matter is made up of still smaller particles which are known as atoms. Hence, it is particulate and is not continuous in nature.
Atom is the basic unit of any matter. Atoms are so small that we cannot see it even through the strongest microscope available, in present.

2. Particles are constantly moving.
All the particles are associated with kinetic energy. Due to this energy, they always remain in motion.
Kinetic energy varies proportionally with square of temperature (i.e., K = 1/2 kT²) and hence, the speed of particles also increases with temperature.

3. They have space in between them.
When we add sugar crystals to water and stir it, we observe that after some time the crystals disappear. The large sugar crystals keep on dividing themselves into smaller and smaller particles and goes into the space in between the water molecules. This shows that there is a lot of space between particles of matter.

4. They are very small in size.
As discussed, atoms are very small in size. The radius of an atom ranges between 10^-10-10^-11 m.
You must have noticed that 1 crystal of salt is so small that we can't see it with our naked eyes. Even that 1 small crystal of salt consist of millions of tiny particles. From this you can conclude that particles of matter are very small.

5. They attract each other.
There are forces in between particles of different matter. These forces keep different particles together. This force is different for solids, liquids and gaseous matter.