8.1 - purity, formulations and chromatography

• If a substance is pure, it only contains one compound or element throughout, not mixed with anything else.
• What will impurities do to a substance?

  Lower the melting point and increase the melting range of a substance.

  • Increase the boiling point and may result in a sample boiling over a range of temperatures.
  • compare the new melting/boiling point with the melting/boiling point of the pure substance
• Formulations are useful mixtures with a precise purpose that are made by following a 'formula'. Each component in a formulation is present in a measured quantity, and contributes to the properties of the formulation so that it meets the required function.
• Name 5 examples of formulations:

  Cleaning products, medicine, baby formula, fertilisers and paints.
• What is chromatography?

  An analytical method used to separate the substances in a mixture. It can be used to identify a substance.
• What are the 2 types of chromatography?

  A mobile phase and a stationary phase.
• What is a mobile phase?

  Where molecules can move - a liquid or a gas.
• What is a stationary phase?

  Where the molecules can't move - solid or really thick liquid
• The amount of time the molecules spend in each phase depends on:

  • how soluble they are in the solvent
  • how attracted they are to the paper
• In paper chromatography, the chromatography paper is he stationary phase and the solvent is the mobile phase.
• Fill in the blanks for the chromatography practical:

  A) paper

  B) beaker

  C) ink spot

  D) water

  
• Each substance on a chromatogram has an Rf value. This is the ratio between the distance travelled by the dissolve substance and the distance travelled by the solvent.
• How do you calculate an Rf value?

  $Rf =$$B/A$
• What does B stand for?

  distance travelled by the substance
• What does A stand for?

  distance travelled by the solvent