MIXTURES AND SOLUTIONS

Mixtures

Mixture Definition: A mixture consists of two or more substances which have been combined such that each substance retains its own chemical identity.That is,  a combination of substances which are not chemically joined together. The key characteristics are:

• They have the same properties as their components
• There is no fixed proportion between the components
• The components can be separated from the mixture

Examples

• A mixture of sugar and salt
• Air is a mixture of gases with nitrogen, oxygen, carbon dioxide, etc.
• A mixture of flour and sugar.
• Salt and sand mixture
• Salt and water

Types of mixtures: There are three types of mixtures.

• Solutions
• Suspensions
• Colloids

Solutions

Definition: A solution is a mixture in which other substances (solutes) are dissolved. The dissolve substance is known as the solute and the substance that does the dissolving is known as the solvent. For example, in a salt solution, the water is the solvent and the salt is the solute.The components in a solution may not be separated from the solution by leaving it to stand or by filtration. Another example is sugar in water.

Degrees of saturation: A solution can be unsaturated, saturated or supersaturated.A solution is unsaturated if it can dissolve more solute at a given temperate. A solution is saturated if no more solute can be dissolved with temperature remaining constant. Note that changing the temperature will affect the solubility. The solubility increases with temperature. A supersaturated solution is the one in which no more solute can dissolve no matter the temperature increase.

Suspensions

A suspension is a mixture of liquids with particles of a solid which may not dissolve in the liquid.The solid may be separated from the liquid by leaving it to stand or by filtration.

Examples

• Sand in water

Colloids

These are homogeneous, noncrystalline substances consisting of large molecules or particles of one substance dispersed through a second substance. 

Examples of colloids are gels, sols, and emulsions; the particles do not settle and cannot be separated out by ordinary filtering or centrifuging like those in a suspension.

Emulsions

This is a fine dispersion of minute droplets of one liquid in another in which it is not soluble or 

miscible. That is, a colloidal suspension of one liquid in another. Emulsions may be temporary or permanent. Temporary ones separate when left to stand for some time.

Examples: Oil and vinegar (temporary emulsion), Mayonnaise (egg yoke in oil) (permanent emulsion)

Certain substances act as emulsifiers. They help two liquids to come together and stay together. Lecithin in the egg yolks acts as emulsifier. It is a fatty substance soluble in both fat and water. In mayonnaise, It combines readily with both the egg yolk and the oil or butter, essentially holding the two liquids together.

Sol

These are colloidal suspensions of small solid particles in a continuous liquid medium. Examples include blood, pigmented ink and paints. If the dispersion medium is water, the colloid is referred to as a hydrosol and if air, an aerosol.

Gels

Gels are colloids in a more solid form than sols. The disperse phase has combined with the dispersion medium to produce a semisolid material. An example is jelly.