8.1 Purity, formulations and chromotography

• What is a pure substance?


  A single element or compound
• How do pure substances behave when heated?


  They melt and boil at specific temperatures
• How can melting and boiling points be used?


  To distinguish pure substances from mixtures
• What is a formulation?


  A mixture designed as a useful product
• What characterises many products in formulations?


  Each chemical has a particular purpose
• How are formulations created?


  By mixing components in measured quantities
• What is chromatography used for?


  To separate mixtures and identify substances
• What are the two phases involved in chromatography?


  A stationary phase and a mobile phase
• What does separation in chromatography depend on?


  The distribution of substances between phases
• What is the formula for Rf value?


  Rf value = distance moved by substance ÷ distance moved by solvent
• How do different compounds behave in chromatography?


  They have different Rf values in different solvents
• What happens to a pure compound in chromatography?


  It produces a single spot in all solvents
• What is paper chromatography?


  A technique separating compounds by speed in solvent
• What does the solubility of a substance affect in paper chromatography?


  The distance it travels up the paper
• What is a pigment?


  A solid, coloured substance
• What are the key characteristics of pure substances and formulations?


  • Pure substances: single element or compound
  • Formulations: designed mixtures with specific purposes
  • Pure substances melt/boil at specific temperatures
  • Formulations are made in measured quantities
• How does chromatography function in separating mixtures?


  • Involves stationary and mobile phases
  • Separation based on distribution between phases
  • Rf values help identify substances
  • Pure compounds yield single spots in solvents