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What is a Mixture?

A mixture is the physical combination of two or more different substances. We can find in our environment a mixture of different types.

There are different kinds of mixtures available, examples include the following: 

Examples of mixture The Earth Crust: This is a mixture of dissolved gases, living organisms and sometimes salts.

Air: This is a mixture or gases, water vapor and dust particles.

Petroleum: A mixture of different hydrocarbons.

Alloys: Contain different elements, e.g., bronze, steel and duralumin.

Coal: A mixture of coal tar, ammoniacal liquor, coal gas, and  coke.

Vulcanizer’s Solution: Contain phosphorus, rubber, benzene and sulphur.

Safety Match Heads: Contain KClO₃ (which is an oxidizing agent and therefore makes it possible for  the match to start burning, because it produces oxygen on decomposition immediately when a sufficiently high temperature has been produced by friction), Fe2O₃, MnO₂ (which acts as catalyst to decompose KClO₃), powdered glass (which acts to produce friction) and antimony sulphide or sulphur (which is the combustible substance).

The side of the box, or the striking surface on the outside of the “book,” is coated with a mixture of powdered glass, red phosphorus and glue. Friction of the match head against this prepared surface causes tiny explosions involving the phosphorus and potassium chlorate. The heat that is thereby liberated ignites the head of the match, which is not readily ignited by friction alone.

Another example of mixture is Gun Powder (containing carbon powder, KNO₃ and sulphur).

Some materials, such as air or a mixture of sugar and water, are homogeneous mixtures; i.e., it is not obvious to the eye that they are composed of more than one substance. The constituents are evenly mixed and form a single phase (no layers are seen). Homogeneous mixtures are usually referred to as solutions. Other materials, such as sand-sugar mixture, are composed of different kinds of particles large enough to be individually seen - they are known as heterogeneous mixtures. The constituents of heterogeneous mixtures are not evenly mixed, but form layers.

When two or more liquids are mixed in all proportions to form a homogeneous mixture, they are said to be miscible, e.g., water and alcohol are miscible. Liquids that do not intermingle to form solutions  are said to be immiscible, e.g., water and gasoline. If two liquids A, and B, are only partially miscible, a limited amount of each will dissolve in the other. If liquid A is present in excess (i.e., more is present that can dissolve in liquid B), two layers form, and each layer is a solution. In one layer the solvent is B, and it contains as much A as can dissolve in it; in the other layer the solvent is A, and it contains as much B as can dissolve in it. Briefly stated, one layer is a saturated solution of A in B, and the other layer is a saturated solution of B in A.

Liquids that are miscible consist of molecules that are of similar character. Non-polar liquids, such as carbon disulphide (CS₂) and carbon tetrachloride (CCl₄) are readily miscible with one another, but they will not dissolve in water because of the high polar nature of water. On the other hand, polar compounds such as methyl alcohol (CH₃OH), and ethyl alcohol (C₂H₅ OH) are miscible with one another and with water.     

Separation of Mixtures