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Key Experimental Techniques in Chemistry

Apr 29, 2025

CAIE IGCSE Chemistry 0620 Theory: Experimental Techniques and Chemical Analysis

Measurement

Variables & Apparatus

  • Time: min/sec, measured with a Stopwatch
  • Temperature: Celsius, measured with a Thermometer
  • Mass: grams, measured with a Balance

Measuring Volume

  • Liquids:
    • Measuring Cylinder: For approximate measures
    • Volumetric Pipettes: For fixed volumes
    • Burettes: For variable volumes
  • Gases:
    • Gas Syringe: Measures volume gradually

Mixture of Substances

  • Mixture: Combination of two or more substances not chemically bonded.
  • Solution: Solute(s) dissolved in a solvent.
  • Saturated Solution: Maximum solute concentration at a given temperature.

Acid-Base Titration

  • Acid added to base until neutralization.
  • Use of indicators to observe color changes:
    • Thymolphthalein: Colorless in acid/neutral, Blue in base
    • Methyl Orange: Red in acid, Orange in neutral, Yellow in base

Filtration

  • Separates insoluble solid from liquid using filter paper and a funnel.

Crystallisation

  • Separates dissolved solid by increasing concentration as the solvent evaporates.
  • Crystals formed and purified by washing and drying.

Simple Distillation

  • Separates solvent from a solution by evaporating and condensing the solvent.

Fractional Distillation

  • Separates miscible liquids using boiling point differences and a fractional column.

Chromatography

  • Separates substances based on solubility in a solvent.
  • Interpretation: Number of spots equals number of substances.
  • Retention Value (Rf): Used to identify substances.

Locating Agents

  • Used to visualize colorless chromatograms by drying and spraying with an agent.

Separation Techniques

  • Use appropriate solvent, filtration, or magnetic properties to separate components.
  • Examples:
    • Solid-Solid: Sand and Salt by dissolution
    • Insoluble Solid-Liquid: Copper (II) Oxide and Water by filtration
    • Soluble Solid-Liquid: Copper (II) sulfate from water by crystallization
    • Liquid-Liquid: Ethanol & Water by distillation or fractional distillation

Purification

  • Purity Assessment:
    • Pure substances have a definite melting/boiling point.
    • Impure substances have altered melting/boiling points.

Identification of Ions and Gases

Test for Cations

  • Aluminum (Al3+): White precipitate with NaOH, colorless in excess.
  • Copper (Cu2+): Light Blue precipitate with NaOH, Dark Blue with excess NH3.
  • Zinc (Zn2+): White precipitate, soluble in excess.

Test for Anions

  • Carbonate (CO): Effervescence with dilute acid.
  • Chloride (Cl): White ppt with silver nitrate.
  • Sulfate (SO): White ppt with barium nitrate.

Gas Tests

  • Ammonia (NH3): Red litmus turns blue
  • Carbon Dioxide (CO2): Turns limewater milky
  • Hydrogen (H2): Squeaky pop with lighted splint

Flame Tests

  • Lithium: Red flame
  • Potassium: Lilac flame
  • Copper (II): Blue-Green flame

Organic Chemistry

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