Understanding Mixtures and Their Separation Methods

Posted on Dec 19, 2024 in Chemistry

Mixtures

Mixtures are formed by joining two or more substances in various proportions, each retaining its own characteristics. There are different types of mixtures based on how the components are combined. If the components of a mixture cannot be distinguished with the naked eye, it is homogeneous. If the components can be differentiated, it is said to be heterogeneous.

Benchmark Optical

This method is used to classify mixtures and is based on direct observation or indirectly through a magnifying glass or microscope.

Classification of Mixtures

  • Heterogeneous: A mixture in which its components can be distinguished with the naked eye or a magnifying glass. The particle size (d) is 10 to 5 cm.
  • Rude: Particle size is very large.

Suspensions

The particles in suspensions are smaller than those in coarse mixtures and are suspended in the liquid for a while.

  • Homogeneous: These have particles that cannot be distinguished with the naked eye, a magnifying glass, or a microscope. They can be:

Solutions

In solutions, the particles are 10-8 cm, where the solute is usually present in a smaller proportion.

Colloids

In colloids, the particle size is between 10-7 and 10-5 cm. There is a dispersed phase that dissolves in a dispersing solvent. A microscope can differentiate between a colloid and a solution, as the particles in a colloid generate constant motion in a zig-zag pattern. The Tyndall effect can also be used, which involves passing a light beam through the mixture in a dark environment. The reflected light is not visible in a solution but is visible in a colloid.

Types of Solutions

Liquid Solutions

These are solutions where the solvent is a liquid.

  • Liquid-solid: Water and salt.
  • Liquid-liquid: Water and acetic acid.
  • Liquid-gas: Water and CO2.

Solid Solutions

These are solutions where the solvent is a solid.

  • Solid-liquid: Formation of an amalgam where the solute is mercury.
  • Solid-solid: Brass, formed by the binding of copper and zinc.
  • Gaseous solutions: These result from the combination of different gases.

Sol: Can be liquid or solid.

Gel: The dispersing phase is a solid, and the dispersed phase is a liquid.

Emulsion: The dispersing phase is a liquid, and the dispersed phase is also a liquid. Alternatively, the dispersed phase can be a liquid, and the dispersant a solid.

Aerosol: A colloid where the dispersed phase is a liquid or solid, and the dispersing phase is a gas.

Foam: The dispersing phase is a liquid or solid, and the dispersed phase is a gas.

Separation of Mixtures

Separation methods are classified into mechanical and physical.

Separating Heterogeneous Mixtures

  • Filtration: Separates two-phase mixtures using a filter with pores through which the substance passes. This separation can be done by gravity or vacuum.
  • Decantation: Consists of separating two liquids that do not mix, or a solid and a liquid. First, tilt the container, allowing the liquid to pour out through a funnel.
  • Sieving: Separates mixtures of solid materials by passing them through a sieve.
  • Magnetization: Separates materials with magnetic properties from those without, using a magnet.
  • Centrifugation: Separates components of different densities using a centrifuge, which spins and separates the denser components.

Separating Homogeneous Mixtures

  1. Evaporation: Separates the components of a solid-liquid mixture.
  2. Extraction: Separates the mixture based on solubility using an appropriate solvent.
  3. Crystallization: A purification method for solids. The process involves dissolving the solute in a hot solvent. Insoluble contaminants are then filtered out while the solution is hot. The solution is then allowed to cool, forming crystals.
  4. Ultracentrifugation: Separates substances.
  5. Electrophoresis: Based on the difference in electrical charges of the substances that form a solution or colloid. By applying an electric field, positively charged particles move toward the negative pole, and negatively charged particles move toward the positive pole.

Distillation

Distillation is used to separate a mixture of two or more substances, where one or more are volatile. The basis of this method lies in the boiling points of each substance, which are then recovered through condensation.

Types of distillation:

  • Simple: Used to separate a substance from its impurities in a liquid. The mixture is heated, causing the volatile substance to separate as a gas. Lowering the temperature yields a pure distillate.
  • Fractional: Used to separate two or more volatile substances. A fractional column is used, which provides a surface for heat exchange. The vapors of the different volatile substances rise and are then cooled with a refrigerant, causing them to condense. This technique is often used to obtain petroleum products.

Chromatography

Chromatography separates the components of a mixture based on the different speeds at which they move when dragged by a solvent (mobile phase) through a porous medium (stationary phase). If the porous medium is paper, it is called paper chromatography. If it is glass flakes, it is called thin-layer chromatography. If it is cotton or glass wool, it is called column chromatography.