Chemical Mixtures, Pure Substances, and Solution Concentration

Pure Substances and Chemical Mixtures

Pure substances are those whose properties are constant and unchanging, serving to identify them. (Mixtures, conversely, have variable properties.)

Types of Pure Substances

• Chemical Element (Simple Substance): A pure substance that cannot be decomposed into simpler pure substances.
• Chemical Compound: A pure substance formed by two or more chemical elements joined together in fixed proportions, which can be separated by chemical reactions.

Mixtures Defined

• Heterogeneous Mixture: The union of two or more substances resulting in a non-uniform appearance, meaning its constituent parts can be visually distinguished.
• Homogeneous Mixture (Solution): The union of two or more substances that results in a uniform appearance, meaning its components cannot be visually distinguished.

Separation Techniques for Heterogeneous Mixtures

These methods are used to separate the components of mixtures based on physical properties like particle size or density.

Methods Based on Particle Size

• Screening (Sieving): A process that allows the passage of particles smaller than the diameter of the mesh holes, separating gross particles.
• Filtration: Used to separate mixtures of solids and liquids. It relies on the difference in particle size. The solid, with coarser particles, is retained on a filter (often filter paper).

Methods Based on Density and Magnetism

• Magnetic Separation (Magnetism): Based on the magnetic properties of one component.
• Settling (Decantation): Used to separate two immiscible liquids based on their different densities. The denser liquid settles at the bottom, and the less dense liquid floats. A separation funnel is typically used.
• Sedimentation: A process for separating solids suspended in a liquid. Solid particles settle to the bottom due to their greater weight (density).

Understanding Solutions and Concentration

Solution Components (Dissolution)

A Solution (Dissolution) is a uniform, well-blended mixture consisting of several pure substances in varying proportions.

• Solvent: The component substance of a solution found in the greater proportion.
• Solute(s): The substance(s) present in smaller amounts.

Classification by Number of Components

• Binary Solution: Contains two components (one solvent and one solute).
• Ternary Solution: Contains three components.

Classification by Amount of Solute

Solutions are classified based on the amount of solute dissolved at a given temperature:

• Diluted: Contains a small amount of solute relative to the maximum possible amount.
• Concentrated: Contains a progressively greater amount of solute (to a greater or lesser extent).
• Saturated: Contains the maximum amount of solute that can dissolve at a given temperature.
• Supersaturated: Contains more solute than the maximum corresponding to that temperature (often an unstable state).

Solution Concentration

The Concentration of a solution is defined as the amount of solute dissolved in a given amount of solvent or the total solution.

Formula for Concentration:

Concentration = Amount of Solute / Amount of Solvent or Solution