Chemical Analysis

• A pure substance is a substance that is made up of only a single element or compound.
• Purity of a substance can be worked out by looking at the melting or boiling points. As pure substances have a specific melting or boiling point.
• Impurities lower the melting point of a substance.
• Impurities increase the boiling point of a substance.
• Formulations are mixtures of chemicals that have been designed to create useful products.
• Examples of formulations are:

  Medicines

  cleaning agents

  fuels
• To ensure that a formulation does what it is supposed to, each chemical component must be present in a precisely measured quantity.
• Chromatography is a process that separates a mixture into its different components.
• 2 phases of chromatography:

  Mobile phase

  Stationary phase
• In paper chromatography, mixtures of soluble substances are separated. A solvent (mobile phase) is run through the mixture on paper (contains the stationary phase). The substances will move up the paper at different rates. The most soluble substance will move the furthest.
• In paper chromatography, the stationary phase is chromatography paper and the mobile phase is the solvent.
• The distance travelled by a spot from where it was applied to when it stops moving is called Rf value.
• What 2 distances are important when calculating Rf values in chromatography?

  Distance travelled by substance

  Distance travelled by solvent
• What does the process of chromatography produce that can be analysed?

  Chromatogram
• Testing for Hydrogen

  • Place a lit splint close to the mouth of a test tube that contains a gas.
  • If the gas is hydrogen, a "squeaky pop" sound will be produced.
• Testing for Oxygen

  • Insert a glowing splint into a test tube that contains a gas.
  • If the gas is oxygen, the splint will relight.
• Testing for Carbon Dioxide

  • Take an aqueous solution of limewater (calcium hydroxide) and bubble through the gas.
  • If the gas is carbon dioxide, the limewater solution will turn from clear to cloudy.
• Testing for Chlorine

  • Insert damp litmus paper into a test tube that contains a gas.
  • If the gas is chlorine, the litmus paper will bleach and change colour from red to white.