C8

• What is the everyday definition of a pure substance?

  A substance with nothing added to it
• What happens to the melting point of a sample with impurities?

  It lowers the melting point
• How do impurities affect the boiling point of a substance?

  They increase the boiling point
• What are formulations?

  • Useful mixtures with a precise purpose
  • Each component is in a measured quantity
  • Contributes to the properties of the formulation
• What is a chemically 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 gas burns quickly with a pop sound?

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

  It relights
• What does chlorine gas do to 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 a pure substance form in chromatography?

  One spot in any solvent
• What does the Rf value represent in chromatography?

  The ratio of distance travelled by substance to solvent
• What is the formula for calculating Rf value?

  Rf = distance travelled by substance / distance travelled by solvent
• What is the significance of the baseline in chromatography?

  • It is the starting point for the sample
  • Indicates where the sample was initially placed
• What is an anion?

  An ion with a negative charge
• What is a cation?

  An ion with a positive charge
• How do you test for halides?

  Add dilute nitric acid and silver nitrate
• What precipitate do chloride ions form?

  A white precipitate of silver chloride
• What precipitate do bromide ions form?

  A cream precipitate of silver bromide
• What precipitate do iodide ions form?

  A yellow precipitate of silver iodide
• How do you test for sulfates?

  Add dilute hydrochloric acid and barium chloride
• What precipitate do sulfate ions form?

  A white precipitate of barium sulfate
• How do you test for carbonates?

  Add dilute acid and connect to limewater
• What happens when carbonate ions react with dilute acid?

  They produce carbon dioxide, turning limewater cloudy
• What are the flame test colors for metal cations?

  • Lithium ions: crimson flame
  • Sodium ions: yellow flame
  • Potassium ions: lilac flame
  • Calcium ions: orange-red flame
  • Copper ions: green flame
• What is a disadvantage of flame tests?

  Colors may be hidden by other ions
• What are the advantages of instrumental analysis?

  • Sensitive: detects tiny amounts
  • Fast: tests can be automated
  • Accurate: provides precise results
• What does flame emission spectroscopy produce?

  A line spectrum of different wavelengths
• How can line spectra be used in analysis?

  To identify ions and determine their concentration
• What happens if multiple ions are present in a sample during spectroscopy?

  • The spectrum will be a combination of their individual spectra
  • Each ion has a unique line spectrum