Understanding Matter: Properties, Changes, and Separation Techniques

Posted on Feb 15, 2025 in Chemistry

Understanding Matter: Properties, Changes, and Separation

Matter is anything made of atoms and molecules. It has mass and occupies volume. Matter possesses general and characteristic properties, such as boiling and melting temperatures. A material system is a piece of matter that can be separated for experimental study.

States of Matter

  • Solid: Fixed mass, volume, and shape. Solids cannot flow (e.g., ice, iron).
  • Liquid: Fixed mass and volume, but variable shape. Liquids can flow (e.g., water, gasoline).
  • Gaseous: Fixed mass, but variable volume and shape. Gases can flow (e.g., CO2, natural gas).

Physical vs. Chemical Changes

  • Physical Changes: Composition does not change.
  • Chemical Changes: Substances change to form new substances with different properties.

Simple Substances and Compounds

  • Simple Substance: A pure substance formed by only one chemical element. It cannot be broken down into simpler substances using ordinary chemical methods.
  • Compound: A pure substance formed by two or more chemical elements always combined in fixed proportions.

Separation by Chemical Methods

  • Thermal Decomposition: A chemical reaction whereby a chemical substance breaks up into at least two chemical substances when heated.
  • Light Decomposition: Light can decompose some compounds into other substances.

Differences Between Homogeneous Mixtures and Compounds

  1. The components of a mixture can exist in any proportion, whereas in compounds, they have a fixed and invariable proportion.
  2. The substances that form mixtures can be separated using physical methods, but the elements that form compounds can only be separated using chemical methods.
  3. The components of mixtures keep their properties; however, compounds have different properties from the elements that form them.
  4. In mixtures, the density, fusion, and boiling temperatures vary with the proportion of the components. In a compound, these properties are characteristic and constant.

Separation by Physical Methods (for Heterogeneous Mixtures)

  • Filtration: A mechanical/physical operation used for the separation of solids from fluids by interposing a medium through which the fluid can pass, but the solids in the fluid are retained.
  • Decantation: A method to separate two immiscible liquids with different densities:
    1. Pour the mixture into a decantation funnel and wait for the substances to separate.
    2. Open the tap and let the denser liquid pass through.
    3. When the denser liquid has passed, close the tap.
  • Magnetic Separation: Separating magnetic solid substances from non-magnetic substances using a magnet.

Solutions

  • Solute: The substance that dissolves to form a solution.
  • Solvent: The substance in which a solute dissolves.
  • Solution: A mixture of one or more solutes dissolved in a solvent.

Solubility

Solubility is the measure of how much solute can dissolve in a given amount of solvent. A solution is called saturated when no more solid will dissolve.

The solubility of a solute at a determined temperature in a determined solvent is the maximum amount of the solute that we can dissolve in 100 g of solvent at this temperature. The solubility of a pure substance in a determined solvent and at a specific temperature is a characteristic property.

Separation Techniques (Chemical) for Solutions

  • Crystallization: The process of formation of solid crystals from a uniform solution. It is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs:
    1. Heat up the solution to evaporate the solvent.
    2. Filter the solution.
    3. Cool it down.
  • Extraction: Based on the relative solubility of a solute in two immiscible solvents.
  • Distillation: Based on the different boiling points of two liquids.