Chemical analysis

• What can a pure substance be classified as?

  A single element or compound
• What characterizes a pure substance?

  It is not mixed with any other substance
• What happens to the temperature of a pure substance during melting?

  It melts at a specific fixed temperature
• What is true about the boiling point of a pure substance?

  It has a specific fixed boiling point
• How do impure substances behave during melting and boiling?

  They melt and boil at a range of temperatures
• What is the melting point?

  When the temperature stops rising
• What is the boiling point?

  Where the temperature stops rising
• What indicates a pure substance regarding melting and boiling points?

  Both points are at a specific fixed temperature
• What does it mean if a substance melts and boils over a range of temperatures?

  The substance is impure
• What is a formulation?

  • A complex mixture designed as a useful product
  • Each component's quantity is carefully measured
  • Ensures the product has desired properties
• What is chromatography used for?

  It is a physical separation technique
• What does paper chromatography separate substances based on?

  Their different solubilities
• What is the stationary phase in paper chromatography?

  The paper that doesn't move
• What is the mobile phase in paper chromatography?

  The solvent that moves
• What does a pure compound produce in chromatography?

  A single spot in all solvents
• How do compounds in a mixture behave in chromatography?

  They may separate into different spots
• Why do we draw the starting line in pencil in chromatography?

  To prevent ink from moving with the solvent
• What is the formula for Rf value in chromatography?

  Rf = distance moved by substance / distance moved by solvent
• What might be necessary if several substances have the same Rf value?

  To repeat using a different solvent
• What is the test for hydrogen gas?

  1. Remove a burning splint from the test tube
  2. Hydrogen burns rapidly and produces a pop sound
• What is the test for oxygen gas?

  1. Use a glowing splint
  2. Place it into the test tube of oxygen
  3. The splint relights
• What is the test for carbon dioxide gas?

  1. Use limewater
  2. Draw gas into a plastic pipette
  3. Bubble gas through limewater
  4. Limewater may turn cloudy after several repetitions
• What is the test for chlorine gas?

  1. Insert damp litmus paper
  2. Chlorine bleaches the litmus paper and turns it white