Properties and Separation Methods of Chemical Substances

Chemical Substances and Mixtures

Chemical substances: N-type material: characteristic properties defined by Cunhas.

Mixtures (Mestura Kimicar)

Mixture: Contains two or more components; often called a chemical mixture (mestura kimicar).

• Heterogeneous (straight): Two or more phases present.
• Homogeneous (homo): One phase present (solution).

Colloidal Dispersions

Colloidal dispersion: A type of heterogeneous mixture in which the phases are not easily distinguished by the microscope. It has two main parts:

• Dispersed phase: The component present in lesser proportion; it is discontinuous and appears as separate particles.
• Dispersing (continuous) phase: The component present in greater proportion; it constitutes the continuous medium.

Solubility

Solubility: The maximum quantity of solute that can dissolve in a given amount of solvent at a specified temperature.

Separation Techniques

Common methods for separating mixtures (S = solid, L = liquid):

• Filtration: Separation of solid and liquid in a heterogeneous mixture using a porous medium (paper with holes).
• Decanting: Separation of solid and liquid or two immiscible liquids by pouring off the top layer (funnel can be used).
• Centrifugation: A method that accelerates the separation of solids and liquids using a centrifuge.
• Evaporation: Separates a dissolved solid from a liquid by removing the liquid (heat and evaporation of the liquid).

Extraction

• Solid–liquid extraction (S–L): Separates a soluble solid from a liquid by transferring the solute into a solvent in which it dissolves preferentially.
• Liquid–liquid extraction (L–L): A dissolved substance is transferred from one liquid to another immiscible liquid that preferentially dissolves it.

Crystallization

Crystallization: Dissolve the substance in a hot solvent (for example, hot water), then allow the solution to cool and crystallize; the remaining solution keeps other components.

Distillation

• Simple distillation: Separates a liquid from non-volatile solutes or separates liquids with very different boiling points using a distillation apparatus.
• Fractional distillation: Separates two liquids with different boiling points into fractions.

Chromatography

Chromatography: A separation technique based on differential adsorption, partitioning, or solubility of components between a stationary phase and a mobile phase.

Natural and Synthetic Substances

• Chemical (pure) substance: A substance with uniform composition and distinct properties (examples: minerals, compounds obtained from plants).
• Natural substances: Obtained directly from minerals, plants, etc.
• Synthetic substances: Obtained in the laboratory from simpler substances.

Physical and Chemical Changes

Physical changes: Changes that alter the appearance or state of a substance but do not change its chemical identity.

Chemical changes: Changes that alter the identity of a substance; chemical reactions produce new substances.

Thermal Decomposition and Electrolysis

• Thermal decomposition: When a substance is heated to high temperatures and breaks down into simpler substances.
• Electrolysis: Decomposition of a substance by passage of an electric current through it.

Elements, Simple Substances, and Compounds

• Element: A species of atoms that make up molecules of simple substances.
• Simple (elemental) substance: Also called an elementary substance; it cannot be decomposed into simpler substances and is formed by one single type of element.
• Compound: A substance formed by two or more combined elements; it can be decomposed into simpler substances.

Synthesis Reactions

Synthesis reactions: Reactions in which two or more simple substances combine to form a compound.