experimental chemistry

Learning Outcomes

  • Knowledge on apparatus for measuring time, temperature, mass, and volume.

  • Ability to suggest suitable apparatus for various experiments.

Apparatus for Measurement

  • Time: Stopwatch

  • Temperature: Thermometer

  • Mass: Electronic balance

  • Volume: Burette, Pipette, Measuring cylinder, Gas syringe

Structure and Properties of Materials

  • Elements: Pure substances; cannot be broken down.

  • Compounds: Two or more elements chemically combined.

  • Mixtures: Two or more substances mixed physically.

Methods of Purification and Analysis

  • Separation and Purification Methods:

    • Filtration

    • Crystallisation

    • Distillation (simple and fractional)

    • Sublimation

    • Paper chromatography

Paper Chromatography

  • Interpretation of chromatograms; use of R_{f} values; necessity for locating agents in colorless compounds.

  • R_{f} value: Ratio of distance moved by substance vs solvent.

Properties of Common Gases

  • Differences in solubility and density of gases.

  • Significant gases include:

    • Ammonia (NH_{3}): high solubility, less dense than air.

    • Hydrogen Chloride (HCl): high solubility, more dense than air.

  • Air composition estimated average Molar mass = 28.96.

Methods for Drying Gases

  • Moisture is removed from gases using drying agents. The choice of drying agent depends on whether the gas is acidic, alkaline, or neutral, as it must not react with the gas being dried.

  • Common Drying Agents:

    1. Concentrated Sulfuric Acid (H{2}SO{4}):

      • It is an acidic drying agent.

      • Used for: Acidic gases like Sulfur Dioxide (SO{2}), Chlorine (Cl{2}), and Hydrogen Chloride (HCl). It is also suitable for neutral gases like Oxygen (O{2}), Hydrogen (H{2}), and Nitrogen (N_{2}).

      • Not used for: Alkaline gases like Ammonia (NH_{3}) because it reacts with them to form a salt.

    2. Quicklime (Calcium Oxide, CaO):

      • It is an alkaline drying agent.

      • Used for: Alkaline gases, specifically Ammonia (NH_{3}).

      • Not used for: Acidic gases like Carbon Dioxide (CO{2}) because a chemical reaction occurs to form Calcium Carbonate (CaCO{3}).

    3. Fused Calcium Chloride (CaCl_{2}):

      • It is a neutral drying agent.

      • Used for: Most gases including Hydrogen (H{2}), Nitrogen (N{2}), and Carbon Dioxide (CO_{2}).

      • Not used for: Ammonia (NH_{3}) because it reacts to form a complex compound.

  • Experimental Set-up:

    • Liquid drying agents (like H{2}SO{4}) are used in a gas wash bottle; the gas delivery tube is immersed in the liquid for bubbling.

    • Solid drying agents (like CaO or CaCl_{2}) are used in a U-tube or a drying tower.

Experimental Design for Gas Collection

  • Consider solubility and density to determine collection methods (upward delivery, downward delivery, or displacement of water).

Methods of Separation & Purification

  • Filtration: Solid-liquid separation.

  • Sublimation: Solid directly to gas.

  • Simple & Fractional Distillation: Separation based on boiling points.

  • Crystallization: Formation of solid from solution.

  • Evaporation: Recovery of solids from liquids.

Purity of Substances

  • Importance of determining purity through melting/boiling points and chromatography.

  • Presence of impurities affects reactivity and safety in food and pharmaceuticals.