Introduction to Chemistry

Tshwane University of Technology

Introduction to Matter and Measurements

Learning Outcomes
  • Describe and classify matter
  • Understand the properties and changes matter undergoes
  • Learn about the separation of mixtures of matter
Definition of Chemistry
  • Chemistry is defined as the study of matter and the changes it undergoes.
States of Matter
Three Physical States of Matter
  • Solid
  • Liquid
  • Gas
  • Example substances:
    • Solid: Water (H₂O) in its solid state (ice)
    • Liquid: Water (H₂O)
    • Gas:
    • Oxygen gas (O₂)
    • Hydrogen gas (H₂)
    • Example provided: Eveready Super Heavy Duty battery, indicating potential chemical reactions involved.
Basic Concepts of Matter
  • Matter: Anything that occupies space and has mass.
  • Represented in three states on Earth: gas, liquid, solid.
Measurement of Matter
  • Mass: How much matter is contained in an object; measured by weighing.
  • Weight: The force with which an object is attracted by gravity; dependent on the planet where the object is located.
States of Matter and Their Characteristics
  • Physical States:
    • Gas: Molecules are far apart and free to move; compressible; indefinite volume.
    • Liquid: Molecules are close enough to allow rotation but have some space; incompressible; indefinite shape but takes the shape of the container.
    • Solid: Molecules are tightly packed; cannot compress; definite shape and volume.
Change of Phase of Matter
  • Melting and boiling (evaporation) require energy for changes in phase (ENDOTHERMIC).
  • Condensation and solidification release energy during phase changes (EXOTHERMIC).
  • Melting point: The temperature at which a solid becomes a liquid.
  • Boiling point: The temperature at which the vapor pressure of a liquid equals the atmospheric pressure.
Classification of Matter
  • Law of Constant Composition: All samples of a given chemical compound have the same elemental composition by mass; for example, water (H₂O) consists of 88.88% oxygen and 11.11% hydrogen.
  • Categories:
    • Pure Substances: Includes elements and compounds.
    • Element: A substance that cannot be decomposed into simpler substances by chemical changes.
    • Compound: A substance composed of two or more elements chemically combined in fixed proportions.
    • Example of compounds: Water (H₂O), Sodium Chloride (NaCl).
    • Mixtures: Combinations of two or more substances where each substance retains its identity; can be separated by physical means.
Types of Mixtures
Homogeneous Mixtures (Solutions)
  • Uniform in composition; constituents cannot be distinguished from one another.
  • Examples include:
    • Saltwater, Steel, Blood, Petrol.
Heterogeneous Mixtures
  • Non-uniform in composition; recognizable different properties can be observed.
  • Examples include:
    • Beach sand, Salad dressing, Water and oil, Water and sand.
Properties of Matter
  • Physical Properties: Characteristics observable without changing the chemical composition. Examples include:
    • Solid, liquid, or gaseous phase of samples.
  • Chemical Properties: Characteristics observed during a chemical reaction, resulting in new substances. Examples:
    • Gold does not react with water (chemical property).
    • Iron rusts in air and moisture (chemical property).
Intensive and Extensive Properties
  • Intensive Properties: Independent of the amount of substance present.
    • Examples: Boiling point, Density, Color.
  • Extensive Properties: Dependent on the amount of substance present.
    • Examples: Mass, Volume, Energy.
Changes in Matter
Physical Changes
  • Occur without changing the chemical composition.
  • Bonds between atoms do not break.
  • The process is reversible; examples include:
    • Phase changes (melting, boiling), Changes in temperature or volume.
Chemical Changes
  • Occur with changes in chemical composition.
  • Bonds between atoms break and new bonds form.
  • The process is generally irreversible; examples include:
    • Combustion, Decomposition, Redox reactions.
Differentiating Physical and Chemical Changes

  • Physical Changes:

    • Affects physical properties; may or may not affect chemical properties.
    • Does not produce new substances; can often be reversed.
    • Examples: Ice melting, Alcohol evaporating.

  • Chemical Changes:

    • Produce new substances with new properties.
    • Generally irreversible; bonds are rearranged.
    • Examples: Iron rusting, Wood burning.
Separation Techniques for Mixtures
  • Filtration: Separates heterogeneous mixtures, solid substances from liquids/solutions.
  • Distillation: Separates homogeneous liquid mixtures based on boiling point differences.
    • Example: Salt water boiling to produce water vapor, which condenses into pure water.
  • Chromatography: Separates substances based on solubility differences in a solvent.
Summary of Key Concepts
  • Matter has mass and occupies volume.
  • Matter exists in different states (solid, liquid, gas).
  • Classification of matter into pure substances (elements, compounds) or mixtures (homogeneous, heterogeneous).
  • Matter exhibits a variety of properties (physical, chemical) and undergoes different types of changes (physical, chemical).
  • Various techniques exist to separate mixtures from one another.