Is Matter Around Us Pure

What is a Suspension?

A heterogeneous mixture in which solute particles do not dissolve but remain suspended throughout the bulk of medium is called a SUSPENSION.

Particles of a suspension are visible to the naked eye.

Example: mixture of flour in water, mixture of oil and water, mixture of powdered chalk in water, mixture of dust and air, etc. are some examples of suspension.

Most of the suspension solutions we encounter in our daily life are solid particles in liquid, such as mixture of chalk powder in water. But suspension could be formed by mixing of two liquid, and even a solid or liquid in a gas.

Properties of Suspensions

Suspension is a heterogeneous mixture.

The particles of a suspension can be seen by the naked eye.

The particles of a suspension scatter a beam of light passing through it and make its path visible.

The solute particles settle down when a suspension is left undisturbed, and hence a suspension is unstable.

Particles of suspension can be separated from the mixture by the process of filtration.

When the particles of a suspension settle down, the suspension breaks and it does not scatter light any more.

Colloidal

What is a Colloidal Solution?

A type intermediate mixture between heterogeneous and homogeneous mixture in which particles remains suspended evenly throughout the mixture is called a colloidal.

Due to the relatively smaller size of particles, as compared to that of a suspension; the mixture appears to be homogeneous, but actually a colloidal solution is a heterogeneous mixture.

Example: milk.

The particles of colloidal are not visible with naked eyes, but a colloidal solution scatter beam of visible light.

Properties of a Colloid

A colloid is a heterogeneous mixture.

The size of particles of a colloid is too small to be individually seen by naked eyes.

Colloids are big enough to scatter a beam o light passing through it and make its path visible.

Particles of colloidal do not settle down when left undisturbed, that is, a colloid is quite stable.

Colloids cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation can be used to separate colloidal particles.

Components of Colloidal Solution

There are two components of a colloidal solution. These are dispersed phase and dispersion medium.

The solute like component or the dispersed particles in a colloid forms the dispersed phase and the components in which the dispersed phase is suspended; is known as the dispersing medium.

This means dispersed phase is solute and dispersing medium is solvent for a colloidal solution.

Classification of Colloids

Colloids are classified according to the state, i.e. solid, liquid, or gas, of the dispersing medium and dispersed phase.

Tyndall Effect

When a beam of light is passed through colloids or colloidal solution, the particles of colloidal solution can easily scatter the beam of visible light, while we cannot see these particles with naked eye.

This scattering of beam of visible light through colloids is called Tyndall Effect.

This effect was discovered by British Physicist John Tyndall. This effect got the name as 'Tyndall Effect' in the honour of this scientist John Tyndall. Tyndall effect is also known as Tyndall Scattering.

Example:

When a beam of light passes through the canopy of dense forest, mist contains tiny droplets of water, which act as particles of colloids dispersed in air, the path of light can be seen easily. This path of light is nothing but visible because of particles of tiny droplets of water and some dust in the atmosphere.

When a beam of light is passes through the slit of door or window in day time, tiny dust particles of dust can be seen easily as dancing. This happens because of Tyndall Effect.

Our eyes colour appear because of tyndall effect. When light passes through the iris the small particles suspended in it makes the path of light visible, and we assume its colour of our eyes.

Separating the Components of a Mixture

Components of mixture can be separated using simple physical processes, such as handpicking, sieving, filtration, etc. Bu many times special techniques are used to separate components of mixture.

Handpicking: Unwanted particles, such as very small stones, husk, etc. are separated from rice in households.

Sieving: Unwanted particles are separated by the method of sieving from wheat flour before making bread.

Filtration: Tea leaves are separated from tea juice by the method of filtration.

Evaporation:

We can separate the volatile component (solvent) from its non-volatile solute by the method of evaporation.

How can we obtain coloured component (dye) from Blue/Black Ink?

Ink is a mixture of dye and some solvent such as water and other binding agents.

Thus, components of ink are dyes and solvent.

The ink and solvent can be separated by one of the simple physical processes evaporation.

Process:

Ink is put in a watch glass over a beaker filled with water.

Water kept in beaker is heated using a burner.

Solvent in ink kept in the watch glass gets evaporated leaving dyes in the watch glass.

Thus, by using the method of evaporation, we can separate dyes from ink.

Separation of salt from the mixture of salt and water, i.e. salt solution

Salt solution in water has two components. First salt (common salt(Sodium chloride)) and water.

When salt solution is heated by keeping in a beaker or other suitable container, water present in solution, gets evaporated leaving salt behind in the beaker.

Similarly, many other components can be separated from their mixture using the method of Evaporation.

Centrifugation

Centrifugation is a process by which solid and denser particles from a colloidal solution are separated out. In the process of centrifugation liquid is spun after keeping in a container forced to move with high speed. In this process the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

In colloidal solutions solid particles are very small and cannot be separated through filter paper by the method of filtration. For mixture having such small particles, the separation of components is done by using the method of centrifugation.

Application of Centrifugation

Used in diagnostic laboratories for blood and urine test.

Separation of Cream from Milk

Milk is a colloidal solution. Fats which are solid particles are dispersed in milk. To separate out fats from milk, the method of Centrifugation is used.

In this milk is spun rapidly after keeping in a container.

Because of centripetal force, denser particles, which are fats, forced to the bottom which is separated out. And lighter part of milk, i.e. water and other constituents are forced to stay at the top.

Thus, by using centrifugation, fats from milk are separated out.

In market one can easily find toned and full cream milk. Toned milk has very less fat while full cream milk has fat.

Used in dairies and home to separate butter from cream.

Used in washing machines to squeeze out water from wet clothes.

Decantation

Two immiscible can be separated using the process of Decantation. In this process liquid which is floated at above layer is poured out leaving the liquid at lower layer in the container.

The principle of decantation is that immiscible liquids separate out in layers depending on their densities.

A separating funnel is used to separate out two immiscible liquids more accurately.

Separating funnel is an apparatus made of glass.

In separating funnel there is a stop-cock fitted with jet in its bottom.

Process:

Mixture of two immiscible liquid is kept in the separating funnel.

After settle of liquid in layers due to their densities, liquid at the lower layer is drained out by opening of stopcock, leaving other liquid in the funnel.

Application of decantation

Decantation is used to separate mixture of oil and water.

Decantation is used in the extraction of iron from its ore, the lighter slag is removed from the top by this method to leave the molten iron at the bottom in the furnace.

Sublimation

There are many solid substances which get converted into gas without converting into liquid when heated. And get converted from gas to solid without converting into liquid after lowering of temperature.

The phenomenon in which a solid substance changes directly from solid to gaseous state on heating and changes directly from gaseous state to solid on cooling is called Sublimation.

Substances that show the phenomenon of sublimation are called sublime volatile substance. For example: naphthalene, camphor, anthracene, ammonium chloride, etc. goes under sublimation.

The process of sublimation is used to separate the components of mixture that contain a sublimable volatile component from a non-sublimable impurity.

How can we separate a mixture of salt and ammonium chloride?

Mixture of salt and ammonium chloride can be separated using the method of sublimation.

Process:

The mixture is kept into a watch glass.

The mixture in watch glass is covered with a funnel, as shown in figure.

The narrow tip of funnel is plugged with cotton.

Now, mixture in the watch glass is heated.

Due to heat, ammonium chloride gets converted into gas and on cooling it gets deposited on inner wall of funnel leaving salt in the watch glass.

Ammonium chloride is separated out by scratching from inner wall of funnel.

And salt is collected separately from watch glass.

Thus, by the method of sublimation, the component of mixture of salt and ammonium chloride is separated.