C12 - chemical analysis

• What do pure substances contain?

  One type of element or compound
• How is 'pure' defined in chemistry?

  As a substance with nothing added to it
• What is an example of a pure substance?

  Pure water
• What are elements made up of?

  One type of atom
• What is an example of an element?

  Oxygen
• What defines a compound?

  Two or more elements chemically joined
• What is an example of a compound?

  NaCl (sodium chloride)
• How are mixtures different from compounds?

  Mixtures are not chemically joined
• What is an example of a mixture?

  A standard cup of coffee
• How do pure substances behave in terms of melting point?

  They have a sharp melting point
• What are formulations?

  Mixtures that produce useful products
• Give examples of formulations.

  Medicines, cleaning products, cosmetics
• What is paper chromatography used for?

  To separate mixtures of soluble substances
• What are the two phases in chromatography?

  Mobile phase and stationary phase
• What is the mobile phase in chromatography?

  The solvent that moves through the paper
• What does a chromatogram show?

  Separation of dissolved substances
• How can chromatography distinguish pure from impure substances?

  Pure substances have one spot on chromatogram
• What is the R value in chromatography?

  Distance travelled by substance / solvent

  
• How can R values help identify substances?

  They compare unknown to known substances
• What is the test for hydrogen gas?

  Burning splint makes a squeaky-pop sound
• How is chlorine gas tested?

  Using damp litmus paper
• What happens to litmus paper in chlorine gas?

  It becomes bleached and turns white
• What is the test for oxygen gas?

  Glowing splint relights in oxygen

  
• What is the test for carbon dioxide?

  Turns limewater cloudy

  
• What do metal ions produce when heated?

  A variety of flame colours
• What is the procedure for flame tests?

  Dip wire loop in sample, heat in flame
• What is the result of adding sodium hydroxide to metal ions?

  Forms precipitates
• What happens to aluminium hydroxide in excess sodium hydroxide?

  It dissolves
• What do ionic equations show?

  Only the ions involved in reactions
• What are spectator ions?

  Ions that do not participate in reactions
• How is a calibration curve used?

  To relate concentration to readings
• What happens to electrons in metal ions during heating?

  They are excited to higher energy levels
• What is the purpose of flame emission spectroscopy?

  To identify metal ions in solution
• What indicates a positive test for carbonate ions?

  Limewater turns milky
• How are halide ions tested?

  With dilute nitric acid and silver nitrate
• What precipitate does chloride produce?

  White precipitate
• What precipitate does bromide produce?

  Cream precipitate
• What precipitate does iodide produce?

  Yellow precipitate
• What is a benefit of flame emission spectroscopy?

  It is rapid, accurate, and sensitive
• What is a drawback of instrumental methods of analysis?

  Equipment is often expensive