chem unit 8

• What is a chemically pure substance?

  A substance made at a specific temperature
• How is a pure substance defined in everyday terms?

  A substance with nothing added to it
• What is the chemical definition of a pure substance?

  A substance containing only one element or compound
• How can you test the purity of a sample?

  By comparing its melting or boiling point
• What effect do impurities have on the melting and boiling points?

  Lower melting point and increase boiling point
• What happens to the melting range when impurities are present?

  It increases with impurities
• What are formulations and their characteristics?

  • Useful mixtures with a precise purpose
  • Each component is present in a measured quantity
  • Each component contributes to the properties
• What gas burns quickly with a pop sound?

  Hydrogen
• What happens to a glowing splint in the presence of oxygen?

  It will relight
• What effect does chlorine have on damp litmus paper?

  It bleaches it white
• What happens to limewater when carbon dioxide is bubbled through it?

  It turns cloudy
• What are the two phases of chromatography?

  • Stationary phase: where molecules can't move (e.g., chromatography paper)
  • Mobile phase: where molecules can move (the solvent)
• What is chromatography used for?

  To separate substances in a mixture
• What does a pure substance form in chromatography?

  Only one spot in any solvent
• What is the R_f value in chromatography?

  The ratio of substance distance to solvent distance
• How is the R_f value calculated?

  R_f = distance travelled by substance / distance travelled by solvent
• How does the R_f value change in different solvents?

  It changes for different solvents
• What does a chromatogram represent?

  The separation of components in a mixture
• What is the baseline in chromatography?

  The starting point for the sample application
• Who was excited to calculate his R_f value?

  Lou