Mixtures

A mixture is an impure substance made up of two or more elements or compounds mechanically mixed together in any proportion.

a. Two elements — Iron and Sulphur.

b. Two compounds — Potassium chloride and Water [potassium chloride solution].

c. Elements and compounds — Sulphur [element], Carbon [element] and Potassium nitrate [compound] mixed together to form gun powder.

The main characteristics of a mixture, with reference to the mixture of iron and sulphur, are:

(i) Components in a mixture are present in varying proportions. — The mixture of iron & sulphur may contain iron & sulphur in varying proportions.

(ii) Mixtures have no definite set of properties. — The components, i.e. elements or compounds in a mixture, retain their original properties. The properties of both iron and sulphur are retained in the mixture of iron & sulphur.

(iii) Components in a mixture can be separated by physical methods. — A mixture of the two elements iron & sulphur can be separated by using a magnet, since iron is attracted to the magnet, which is a physical method.

a. Sieving — Based on the difference in size of the solid particles.

b. Magnetic separation — Based on the difference in magnetic & non-magnetic nature of the particles.

c. Sublimation — Based on the difference in sublimable & non-sublimable nature of the solids.

a. Sedimentation & decantation — Based on the settling down by gravity of the insoluble solid particles in an insoluble solid-liquid mixture, followed by pouring out of the liquid.

b. Filtration — Based on the filtration of insoluble solid particles in a solid-liquid mixture.

c. Evaporation — Based on the evaporation of the liquid component in a soluble solid-liquid mixture.

Sieving — It is a method of separating a solid-solid mixture, based on the difference in the size of the solid particles.

Structure of a sieve — A sieve is a wooden frame with a metal mesh.

Separation of different sized particles by sieving — The large sized particles are separated from the small or finer particles by passing the mixture through a sieve. On shaking the sieve, the larger particles stay above while the finer particles pass through and collect below it.

Magnetic separation — It is a method of separating a solid-solid mixture, based on the difference in the magnetic & non-magnetic nature of the particles.

Separation of iron from sulphur — The magnetic particles of iron are separated from the non-magnetic particles of sulphur by utilizing the magnetic properties of iron. When a magnet is moved over the mixture, the iron gets attracted to the magnet and separates out from the non-magnetic sulphur, which remains behind.

Sublimation is based on the difference in the sublimable & non-sublimable nature of the solids. When a mixture of a sublimable and a non-sublimable substance is heated, the sublimable solid sublimes i.e. turns directly into vapour and condenses elsewhere, while the non-sublimable solid remains behind. Hence, they can be separated easily.

However, when two sublimable substances are heated together, both turn into vapour on heating and condense together. As neither remains behind, two sublimable substances cannot be separated by sublimation.

Insoluble solid particles in a solid-liquid mixture are separated by filtration.

Technique — A filter paper is made into a cone & placed in a funnel. The solid-liquid mixture is poured through it. The solid particles remain behind on the filter paper while the liquid passes through and collects below.

Sedimentation	Decantation
It is the process of settling down by gravity of the insoluble solid component in a solid-liquid mixture, on standing for some time.	It is the process of pouring out of the liquid, such that the solid that has settled down remains behind.

Experimental technique — The insoluble solid component in the solid-liquid mixture settles down on standing in a beaker [sedimentation]. The liquid which collects above it is then carefully poured out, leaving the solid behind in the beaker [decantation].

A solid component in a soluble solid-liquid mixture is separated by evaporation.

Technique — The soluble solid is separated from its liquid component by allowing the liquid component to evaporate either on its own or by heating. During evaporation, the liquid component is lost to the atmosphere as vapour and the soluble solid remains behind.

a. Coarse sand from fine sand — by sieving.

b. A magnetic particle from a non-magnetic particle — by magnetic separation.

c. Naphthalene from sodium chloride — by sublimation.

d. Chalk & water using a filter paper — by filtration.

e. Sand & water without using a filter paper — by sedimentation & decantation.

f. Common salt from a solution of common salt & water — by evaporation.

a. Iodine crystals & potassium chloride — Sublimation

b. Iron & chalk powder — Magnetic separation

c. Potassium chloride from an aqueous solution of potassium chloride — Evaporation

d. Rice powder from soil particles — Sieving

e. Iron filings from pieces of copper wire — Magnetic separation

f. Large diamonds from very small diamonds — Sieving

(i) False.
Correct Statement — Components in a mixture are present in any [varying] proportion.

(ii) True.

(iii) False.
Correct Statement — Components in a mixture can be separated by physical methods only.

(iv) False.
Correct Statement — Sodium chloride and water is an example of a mixture of two compounds.

(v) True.

(i) Carbon [charcoal]

(ii) Magnetic separation

(iii) The liquid component [water]

(iv) Sodium chloride [the non-sublimable component]

(v) Oil & water

(i) Both naphthalene & camphor are sublimable substances. On heating, both sublime and turn into vapour together, so neither remains behind. Hence, they cannot be separated by sublimation.

(ii) Sodium chloride is soluble in water and forms a solution. The dissolved salt particles pass through the pores of the filter paper along with the water. Hence, sodium chloride cannot be separated out from its aqueous solution by filtration.

(iii) Sieving is based on the difference in the size of the solid particles. Two varieties of wheat flour have particles of nearly the same size, so both pass through the sieve together. Hence, they cannot be separated by sieving.

(iv) Magnetic separation is based on the difference in the magnetic & non-magnetic nature of the particles. Both sulphur and charcoal powder are non-magnetic and neither is attracted to the magnet. Hence, they cannot be separated by magnetic separation.

(v) During evaporation, the liquid component is lost to the atmosphere as vapour and only the soluble solid remains behind. As the liquid component is not recovered, both components of a soluble solid-liquid mixture cannot be recovered by evaporation.