C8-Chemical analysis

• What is the everyday definition of a pure substance?

  A substance with nothing added to it
• What does a chemically pure substance do at a specific temperature?

  Melt at a specific temperature
• What effect do impurities have on the melting point of a sample?

  Lower the melting point and increase the melting range
• How can you test the purity of a sample?

  By comparing its melting or boiling point
• What is a formulation?

  A useful mixture with a precise purpose
• What is the role of each component in a formulation?

  Each is present in a measured quantity
• What are the four tests for gases?

  1. Hydrogen: Burns with a pop
  2. Oxygen: Relights a glowing splint
  3. Chlorine: Bleaches damp litmus paper white
  4. Carbon Dioxide: Turns limewater cloudy
• What sound does hydrogen make when ignited?

  Burns with a pop
• What happens to a glowing splint in the presence of oxygen?

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

  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: Molecules can't move (e.g., chromatography paper)
  • Mobile phase: Molecules can move (e.g., water or ethanol)
• What does the amount of separation in chromatography depend on?

  How each substance is distributed between phases
• What is the Rf value in chromatography?

  The ratio of distance travelled by substance to solvent
• If a substance travels further in chromatography, what does it indicate?

  It is less attracted to the stationary phase
• How does the Rf value change in different solvents?

  It changes for different solvents
• What does a pure substance form in any solvent during chromatography?

  One spot
• What is the baseline in chromatography?

  The starting line for the sample application
• What does the solvent front indicate in chromatography?

  The distance moved by the solvent
• What happens to the number and position of spots in different solvents?

  They can change in different solvents
• What is the purpose of paper chromatography?

  To separate and identify substances
• What is the significance of the distance travelled by the solvent in chromatography?

  It helps calculate the Rf value
• How does the distribution of substances affect their movement in chromatography?

  It determines how far they travel