Chapter 2: Experimental Techniques

Elements, Compounds, and Mixtures

  • Element: Simplest substance, cannot be broken down, made of identical atoms/molecules.

  • Atom: Basic unit of matter, defines chemical properties of an element.

  • Molecule: Two or more atoms chemically bonded.

  • Ion: Electrically charged atom/group of atoms (anion: negative, cation: positive).

  • Compound: Two or more elements chemically combined in specific proportions.

  • Mixture: Substance composed of multiple components, easily separated physically.

    • Heterogeneous: unevenly mixed, easily separated (filtration, magnet).

    • Homogeneous: evenly mixed, requires processes like distillation or chromatography for separation.

Measurement

  • Units: Uses International System of Units (SI units).

  • Time:

    • Tool: Digital stopwatch/timer.

    • Unit: Seconds (s).

  • Temperature:

    • Tool: Thermometer.

    • Unit: Kelvin (K), Celsius (°C).

  • Mass:

    • Tool: Digital balance.

    • Unit: Kilogram (kg), gram (g).

  • Volume (Liquid):

    • Tool: Measuring cylinder, burette, volumetric pipette.

    • Unit: cm33 .

  • Volume (Gas):

    • Tool: Gas syringe.

    • Unit: m33 , cm33 .

Scientific Methods

  • Process: Problem → Hypothesis → Experiment → Data Collection → Data Analysis → Conclusion.

  • Advantages: High control level, cause-effect determination.

  • Disadvantages: Subjectivity, can be costly and time-consuming.

Solutions and Solubility

  • Solute: Substance that dissolves.

  • Solvent: Substance that dissolves the solute.

  • Solution: Mixture of solute and solvent.

  • Aqueous Solution: Water as the solvent.

  • Saturated Solution: Maximum solute dissolved at a specific temperature.

  • Solubility increases with temperature.

Separation and Purification Techniques

  • Filtration: Separates solid-liquid mixtures.

  • Crystallization: Purifies solids by forming crystals.

  • Simple Distillation: Separates liquids with different boiling points.

  • Fractional Distillation: Separates miscible liquids with close boiling points.

  • Chromatography: Separates solutes in a solution.

    • Locating agents are used for colorless solutes.

    • Rfvalue:value:Rf = {distance travelled by substance}/ {distance travelled by solvent}

Purity

  • Essential for food and drugs to prevent side effects.

  • Paper chromatography can identify purity.

  • Pure substances have sharp melting/boiling points, while impure substances have a broader range due to the disruption of the crystal lattice..