Experimental Chemistry

This note covers the principles of designing chemical experiments, identifying variables, writing procedures, assessing risks, and common purification techniques used to separate mixtures and assess purity.

1. Experimental Design
  • 🔹 Designing Experiments:

    🔹 Plan investigations with clear objectives to study chemical phenomena systematically.

  • 🔹 Key Variables:
    • 🔹 Independent Variable:

      🔹 The variable that is deliberately changed.

    • 🔹 Dependent Variable:

      🔹 The variable that is measured or observed.

    • 🔹 Control Variables:

      🔹 Variables that are kept constant to ensure a fair test.

  • 🔹 Procedures:

    🔹 Write clear, step-by-step instructions including materials, methods, and conditions for reproducibility.

  • 🔹 Risks and Precautions:

    🔹 Identify hazards and apply safety measures such as protective equipments, proper handling, and emergency plans.

2. Methods of Purification and Analysis
  • 🔹 Purification Techniques:
    • 🔹 Filtration:

      🔹 Separates solids from liquids by passing mixture through filter paper.

    • 🔹 Distillation:

      🔹 Separates liquids based on different boiling points.

    • 🔹 Chromatography:

      🔹 Separates mixture components based on movement through a stationary phase.

    • 🔹 Locating Agents:

      🔹 Used in chromatography to reveal colorless compounds, e.g., iodine vapour, UV light.

  • 🔹 Identity and Purity:

    🔹 Melting and boiling points indicate purity—pure substances have sharp points matching known values; impurities cause changes.

  • 🔹 Importance of Purity:

    🔹 Ensures safety and quality in food, drugs, and everyday products by removing harmful impurities.

  • ⚠️ Control variables can be changed during an experiment; they must be kept constant.
  • ⚠️ Filtration can separate dissolved substances; it only separates solids from liquids.
  • ⚠️ Chromatography always produces colored spots; locating agents may be needed for colorless substances.
  • ⚠️ Impurities always raise melting points; they usually lower and broaden melting ranges.

  • 👉 Clearly identify and label independent, dependent, and control variables in experiment design questions.
  • 👉 Describe purification techniques with appropriate diagrams where possible.
  • 👉 Explain how melting and boiling points reflect purity.
  • 👉 Highlight safety measures when designing experimental procedures.

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