Understanding Mixtures and Separation Techniques

What is a Mixture?

A mixture is a substance formed by combining two or more substances without a chemical reaction occurring that changes its components.

• A homogeneous mixture is one in which no substance loses its original properties and can be separated by physical means. It has a uniform composition throughout.
• A heterogeneous mixture is one that has a non-uniform composition in which components can be distinguished by the naked eye and consists of two or more physically distinct substances, unevenly distributed.

Physical Separation Techniques

Distillation

Distillation is used to separate two liquids with different boiling points by heating and subsequent condensation of the substances. The distillation process consists of two phases: first, the liquid becomes steam, and second, the vapor condenses back to liquid.

Evaporation

Evaporation is used to separate the components of a mixture of a solid dissolved in a liquid. Evaporation takes place in shallow containers with a large surface area, such as porcelain crystallizers.

Crystallization

Crystallization is used to purify a solid substance. This is accomplished by dissolving the solid in a hot solvent in which contaminants are not soluble, then filtering it hot to remove impurities, and then allowing it to cool slowly until crystals form.

Chromatography

Chromatography is the technique used to separate the components of a mixture according to the different speeds with which they move when carried by a solvent through a porous medium that supports the mixture. It is based on the relative amounts of each solute distributed between a moving fluid, called the mobile phase, and an adjacent stationary phase.

Column Chromatography

Column chromatography involves placing the absorbing substance in a glass tube. The mixture of substances to be separated is added to the upper end, followed by a suitable solvent to dissolve the substances.

Paper Chromatography

Paper chromatography is used to separate the components of mixtures like tomato sauce or plant pigments.

Mechanical Separation Techniques

Filtration

Filtration consists of separating the components of a mixture of two phases, solid and liquid, using a permeable membrane called the filter medium. The mixture is passed through the filter; the liquid phase passes through the membrane, and the solid phase is retained.

Sieving

Sieving consists of separating a mixture of solid materials of different sizes, such as beans and grains of sand, using a sieve (strainer). The sand grains pass through the sieve, and the beans are retained.

Magnetization

Magnetization uses a magnet to separate the components of a mixture where one is a magnetic material and the other is not. The separation is done by passing a magnet through the mixture so that the magnetic material is affixed to it. For example, separating iron filings mixed with powdered sulfur. It is sufficient to hold the magnetic component with a magnet and tilt the bowl containing the two materials, so you can collect the liquid in another container.

Centrifugation

Centrifugation is the separation of materials of different densities that form a mixture. The mixture is placed inside a device called a centrifuge, which rotates constantly and rapidly, causing the denser particles to go to the bottom and the lighter ones to remain at the top.

Decanting

Decanting is used to separate two liquids of different densities or a mixture consisting of an insoluble solid in a liquid. If we have a mixture of a solid and a liquid where the solid does not dissolve, allow the mixture to settle, and the solid will go to the bottom of the container. If there is a mixture of two liquids, it is placed in a separating funnel, allowed to settle, and the denser liquid will be at the bottom of the funnel.