When two or more chemically non-reacting substances are mixed, they form mixtures. A mixture may be heterogeneous or homogenous. A heterogeneous mixture consists of distinct phases and the observed properties are just the sum of the properties of individual phases. However, a homogenous mixture consists of a single phase which has properties that may differ drastically form those of the individual components.

 

A homogenous mixture whose composition can be varies within certain limits is termed a true solution.

 

The constituents of a solution cannot be separated by filtration, setting or centrifugal action. All solutions are characterized by (i) homogeneity, (ii) absence of settling and (iii) the molecular or ionic state of sub-division of the components.

 

When the solution is composed of only two chemical substances, it is termed a binary solution. Similarly, it is called ternary and quaternary if it is composed of three of four components, respectively. Thus, a solution may be regarded as a single phase containing more than one component.

 

 

Every solution consists of a solvent and one or more solutes. Solvent in a solution is its constituent as that of the solution. Generally, the component present in greater amount than any or all the other components is called the solvent. For the solubility of solids in liquids, where the liquid is present in large excess over the solid, there is no ambiguity in these terms, the solid being the solute and the liquid being solvent. However, if the solution is the same as that of a component present in smaller amount, the latter is called the solvent. For example, in a syrup (liquid solution) containing 60% sugar (a solid) and 40% water (a liquid – same aggregation as solution), water is termed as the solvent. In a solution of alcohol and water, the substance present in a larger proportion by mass is called the solvent. But if both the liquids have same masses in solution, it becomes difficult to differentiate between solvent and solute.