classification of mixtures

1. It is applied in the separation of mixtures in the laboratory
2. Extraction of some mineral such as common salt

Many mixtures contain useful substances combined or mixed with unwanted materials. In order to obtain these useful substances chemists have to separate them from the impurities. They have developed many different methods of separating the mixtures. The separation depends on what properties of the substance contain.

1. Decantation
2. Evaporation
3. Distillation (simple distillation and fraction distillation)
4. Sublimation
5. Filtration
6. Chromatography
7. Layer separation
8. Solvent extraction

Is the process of separating a heterogeneous mixture of a liquid and a solid. This is the process of separating solids by pouring out the liquid and only remaining with the solid at the bottom of the container.

The water in the oceans, lakes and rivers are heterogeneous mixtures that contain sand and insoluble matter that later settles at the bottom when water settles. The process of the components of some of the mixture settling at the bottom is called sedimentation. It is the first step in decantation. When muddy water is left to stand for sometime the mud settles at the bottom of the container and clear water comes on top. Also decantation is usually used in the blood tests which require the part of blood to be separated from solid components.

Is the process of separating a solute from a liquid. The solvent is then converted from liquid to gas through heating the solute that remains as a residue. When a solution of a common salt in water is heated until it evaporates, while solid crystals of the salt are obtained.

Is the process of separating a mixture by heating a liquid to a very high temperature until it vaporizes in other words turns into a gas. This gas is then cooled until it turns back into liquid. The cooled vapor is called distillate. There are two types of distillation.

1. Simple distillation
2. Fractional distillation

Simple distillation

This is used to separate liquids containing dissolved substances. An example is distilling water from muddy water.

Simple distillation

• The condenser helps to cool the steam by means of the water that flows in and out of the condenser. The distillate is pure water and therefore is colorless.

• In a situation where there is no condenser, the distillate is collected in a test tube that is deepen in a beaker containing very cold water or ice.

Fractional distillation

This is the method of separating a mixture of two or more liquid that forms a heterogeneous solution by means of a fractionating column. The liquids are said to be miscible. A good example is ethanol and water, since the two liquids have different boiling points but very close boiling points whereas the solution can be separated by careful heating. The liquid with a lower boiling point is the 1st one to be collected as a distillate. Each component collected is known as a fraction

Fractional distillation

• When a mixture of ethanol and water is heated the ethanol distills first at a temperature of about 78.4°C, this is its boiling point. The boiling point of pure water is 100°C.

• The fractionating column separates the two. The one with a lower boiling point, ethanol, moves to the upper of the column and distills over. Water which has a higher boiling point will tend to stay at the bottom of the column until the ethanol distills over.

This is the method used for separating immiscible liquids using a separating funnel. Immiscible are those that do not mix at all but form distinct layers when put together. The most dense remains at the bottom.

• Poured into the separating funnel they both move to the top of the funnel whereas water is drained out first. Materials used for this method are such as separating funnel, kerosene, water, cooking oil, beaker.

This is a process whereby solid changes directly to gas usually on heating.

• The solid that is formed after the vapor cools is called a sublimate. The process can be used to separate mixtures where one of the substances sublimes. Iodine and ammonium chloride are among the few compounds that will be changed directly from solid to gas when heated.
• The reverse process of vapor changing to solid on cooling is called deposition. Materials used are iodine, ammonium chloride, common salt etc. Other apparatus are Bunsen burner, wire gauze, beaker. When a mixture of iodine and sand is heated the iodine sublimes and then condenses at the bottom of the flask, the sand remains in the beaker.

This is the method used to separate a heterogeneous mixture of a solid and a liquid.

• Some chemical reaction produce insoluble solid and the mixture can be separated by this method. The solid is separated from the mixture using a filter such as a paper, the solid obtained is the residue and the liquid is the filtrate. Materials and apparatus used are muddy water, filter funnel, conical flask, retort stand and clamp.

This is the process of separating mixtures using a moving soft material that absorbs solvent.

• Chromatography is used to separate a mixture of substances into their components so that they can be analyzed and identified. The moving solvent is called mobile phase many may be a liquid or gas. The material that absorb solvent is called stationary phase.

This is the process of extracting essential oils from plant materials especially seeds using liquid that dissolves the oil. The oil is distilled and the solvent is left to evaporate, the process is referred to as liquid extract. For example seeds which are used to extract oils.