CHEM Experimental Chemistry

Physical Quantities

  • Time: SI unit is second (s), measured with a stopwatch (accuracy: ±0.01 s to ±0.1 s).
  • Temperature: SI unit is kelvin (K), measured with a thermometer (accuracy: ±0.1°C to ±0.5°C). (K = °C + 273)
  • Length: SI unit is metre (m), measured with a metre rule or measuring tape (accuracy: ±0.1 cm).
  • Mass: SI unit is kilogram (kg), measured with an electronic balance (accuracy: ±0.001 g to ±0.01 g).
  • Volume: SI unit is cubic metre (m^3), measured with a burette (accuracy: ±0.05 cm^3), pipette (accuracy: ±0.01 cm^3), measuring cylinder (accuracy: ±0.5 cm^3 to ±1 cm^3), or gas syringe (accuracy: ±0.5 cm^3 to ±1 cm^3).
  • 1 m^3 = 1000 dm^3 = 1,000,000 cm^3

Separating Mixtures

  • Solid-Solid Mixtures
    • Magnetic attraction: separates magnetic substances.
    • Sieving: separates based on particle size.
    • Using suitable solvents: separates based on solubility.
  • Solid-Liquid Mixtures
    • Filtration: separates insoluble solids from liquids; residue is solid on filter paper, filtrate is liquid that passes through.
    • Evaporation to dryness: separates a dissolved solid from its solvent by vaporizing the solvent.
    • Crystallization: obtains a pure solid from a saturated solution.
  • Liquid-Liquid Mixtures
    • Simple distillation: separates a pure solvent from a solution.
    • Fractional distillation: separates miscible liquids with different boiling points using a fractionating column.
    • Chromatography: separates substances with different solubilities in a given solvent.

Chromatography

  • Separates mixtures based on different solubilities in a solvent.
  • Chromatograms show separated substances; comparison with known substances identifies components.
  • Applications: identifying unauthorized substances in food, detecting banned substances in athletes, separating DNA fragments.

Distillation

  • Simple Distillation: Used to separate a pure solvent (liquid) from a solution.
  • Fractional Distillation: Used to separate miscible liquids with different boiling points; utilizes a fractionating column.
  • The initial distillate collected will contain the substance with a lower boiling point.
  • Longer columns improve separation of liquids with close boiling points.

Collecting Gases

  • Method depends on gas solubility in water and density compared to air.
  • Water displacement: for insoluble or slightly soluble gases.
  • Downward delivery: for gases denser than air.
  • Upward delivery: for gases less dense than air.

Purity of Substances

  • Pure substances have specific melting/boiling points; mixtures melt/boil over a range.
  • Impurities lower melting points and raise boiling points.