SEPARATING MIXTURE

PURE SUBSTANCES and MIXTURES

When we do an experiment, we often end up with a mixture of substances rather than just one. We must know how to separate the mixtures.

A single substance that has no other substances mixing with it is called a PURE SUBSTANCE. If there is something else mixed with it, it is a mixture.

SOLID/LIQUID MIXTURES

The mixture of dissolved salts in water is an example of a solid/liquid mixture. The mixture is clear and no salt can be seen. We called this sort of mixture a solution. The solid which dissolves, such as salt, is called the solute. The liquid that solute dissolves, such as water, is called the solvent. Solids such as sugar and salt that dissolve are describe as soluble. Solids such as mud and coin which do not dissolve are described as insoluble.

SOLUTE + SOLVENT = SOLUTION

We often say that a solution that contains a little solute in a given amount of solvent is dilute. We called a solution contains a lot of solute in a given amount of solvent CONCENTRATED.

We called a solution SATURATED when it can dissolved all the solute. Usually cold solvents dissolve less solute than hot solvents.

A saturated solution is a solution which has dissolved all the solute, at a given temperature.

An aqueous is to describe water when it is used as a solvent. Water is the most common solvent, however the are many other solvents which we used in industry and around houses. They are all needed to dissolve substances that cannot be dissolve in water.

SUSPENSIONS

Sometimes it is hard to distinguish between a cup of PURE water and a cup of salt in water mixture just by looking, but there are times we can easily recognize a mixture. For example, By looking at the chalk in water in the diagram below. We can see there are white specks in the water, since chalk cannot dissolve in water. The particles of chalk are suspended in water. They are so light which they will not sink. We called this sort of mixture a suspension. Insoluble solid particles are suspended throughout the liquid in the process of suspension. They are in groups that they are large enough for us to see.

LIQUID/LIQUID MIXTURES

We used to word MISCIBLE when liquids mix together completely in order to form one single liquid. We called those liquids which cannot mix together completely IMMISCIBLE. Oil and water form two separate layers when they are mixed.

The reason which we need to pure substance is because in Chemistry, pure substances are needed to produce drugs or perform experiments in the laboratory. However, most substances obtained from nature are mixtures. Therefore these mixtures need to be separated and purified before we can use them.

METHODS of PURIFICATION and SEPARATION

Purification and separation of substances are very important techniques in Chemistry. Some of the common methods of purification and separation are explained in the other sections.