1.2 Elements, Compounds and Mixtures

• Rf value


  Retardation factor, calculated as distance moved by spot / distance moved by solvent front, used to identify components of a mixture
• Element


  The smallest unique form of matter, consisting of only one type of atom. Represented as single circles in diagrams and grouped in the Periodic Table (118 elements, some natural, some synthetic)
• Compound

  A substance formed when two or more different elements chemically bond (e.g., CO₂)
• Molecule

  A substance containing multiple atoms. Diatomic substances (e.g., H₂, O₂) are considered molecules
• Mixture


  Contains different elements that are not chemically bonded (e.g., a mixture of gases)
• Filtration


  • Used to separate a solid from a liquid.
  • Example: Separating sand from water.
  • The solid left is called the residue, and the liquid that passes through is the filtrate.
• Crystallisation


  Used to reform solid crystals from a solution by heating to evaporate the solvent and then cooling the saturated solution
• Simple Distillation

  • Separates a solute from a solution or two liquids with different boiling points.
  • Example: Producing salt-free water from seawater.
• Fractional Distillation:

  • Separates mixtures of liquids with close boiling points.
  • Example: Separating ethanol (boils at 78°C) from water (boils at 100°C).
• Paper Chromatography


  1. Used to separate mixtures, such as food colorings or pigments in leaves

  2. Relies on the different affinities and solubilities of substances in the solvent
• Paper Chromatography Experiment

  1. Draw a pencil line 1 cm from the bottom of the chromatography paper

  2. Apply a small amount of dye mixture on the pencil line and let it dry

  3. Place the paper in a beaker with a small amount of solvent below the pencil line

  4. Cover the beaker to prevent solvent evaporation

  5. Observe the distance traveled by different dyes and calculate the Rf value: Rf value=distance moved by spot / distance moved by solvent front
• Separation Methods

  • Potassium iodide from solution: Crystallisation
  • Water from potassium iodide solution: Simple Distillation
  • Blue dye from a mixture of red and blue dyes: Paper Chromatography
  • Calcium carbonate from a mixture with water: Filtration
• Simple Distillation

  • Process:

  1. Heat salt solution in a distillation apparatus.
  2. Water evaporates and vapour travels into the delivery tube.
  3. Condenser cools the vapour, causing it to condense.
  4. Outcome:

  • Salt crystals remain in the original flask.
  • Distilled water collects in a separate flask.
• Filtration:

  • Purpose: Separate a solid from a liquid.
  • Process:

  1. Pour the mixture into a funnel lined with filter paper.
  2. Residue: Solid left on the filter paper.
  3. Filtrate: Liquid that passes through the filter paper.
  4. Can also separate two solids if one is soluble in water.
• Crystallisation:

  • Purpose: Reform solid crystals from a solution.
  • Process:

  1. Heat the solution to evaporate the solvent.
  2. Cool the saturated solution.
  3. Crystals of the solute will form and can be collected.
• Fractional Distillation:

  • Purpose: Separate liquids with close boiling points.
  • Example:

  1. Ethanol and water mixture.
  2. Ethanol boils at 78°C, water at 100°C.
  3. Ethanol vapour rises and condenses first.
  4. Collect ethanol in a separate vessel.
• Paper Chromatography:

  • Purpose: Separate mixtures of soluble substances.
  • Process:

  1. Draw a pencil line 1 cm from the bottom of the paper.
  2. Apply dye mixture to the line and dry.
  3. Place paper in a beaker with solvent below the pencil line.
  4. Cover the beaker.
  5. Observation: Different substances travel different distances.
  6. Rf Value: Rf value = distance moved by spot / distance moved by solvent front
• Sea Water

  Mixture. Contains water, dissolved salts, and other impurities
• Magnesium Oxide

  Compound. Consists of magnesium and oxygen chemically bonded (MgO)
• Calcium


  Element. Pure substance consisting of only calcium atoms (Ca)
• Hydrogen

  Element. Pure substance consisting of only hydrogen atoms (H₂)
• Copper(II) Sulfate

  Compound. Consists of copper, sulfur, and oxygen chemically bonded (CuSO₄)
• Mud

  Mixture. Contains water, soil, and organic matter mixed together but not chemically bonded
• Honey

  Mixture. Contains various sugars, water, and other components not chemically bonded
• Blood

  Mixture. Contains red and white blood cells, plasma, and other components not chemically bonded
• Potassium Iodide Solution

  Mixture. Consists of potassium iodide dissolved in water, forming a solution
• Chromatogram: A graph showing how far each substance has travelled along the chromatography paper compared to the distance travelled by the solvent front.
• The further up the chromatogram a spot appears, the more soluble the substance is in the mobile phase (solvent). The closer to the starting point, the less soluble the substance is in the mobile phase.
• Solvent Front: The point where the solvent reaches on the chromatography paper.
• Rf Value: The ratio between the distance traveled by a spot and the distance traveled by the solvent front.