Identification of ions by chemical and spectroscopic means

• What can flame tests be used to identify?

  Metal ions
• What color flame does lithium produce?

  Crimson
• What color flame does sodium produce?

  Yellow
• What color flame does potassium produce?

  Lilac
• What color flame does calcium produce?

  Orange-Red
• What color flame does copper produce?

  Green
• What happens to flame colors when a mixture of ions is tested?

  Some flame colors can be masked
• What precipitate do aluminium, calcium, and magnesium ions form with NaOH?

  A white precipitate
• Which metal ion's precipitate dissolves when excess NaOH is added?

  Aluminium
• What color precipitate does copper(II) produce?

  Blue
• What color precipitate does iron(II) produce?

  Green
• What color precipitate does iron(III) produce?

  Brown
• What is the equation for the reaction of copper ions with hydroxide ions?

  Cu$^{2+}$ + 2OH$^{-}$ -> Cu(OH)$_{2}$
• How many OH$^{-}$ ions are needed for each metal ion charge?


  As many as the charge on the metal ion
• What happens to Na from NaOH in the precipitation reaction?

  It reacts to form a compound with the metal ion
• What is produced when carbonates react with dilute acids?

  Carbon dioxide
• How can you test for carbon dioxide gas?

  Bubble it through limewater
• What indicates the presence of carbon dioxide in limewater?

  The limewater goes cloudy
• What is the first step in testing for halides?

  Add dilute nitric acid
• What precipitate does chloride produce when tested with silver nitrate?

  A white precipitate
• What precipitate does bromide produce when tested with silver nitrate?

  A cream precipitate
• What precipitate does iodide produce when tested with silver nitrate?

  A yellow precipitate
• What is the first step in testing for sulfates?

  Add dilute hydrochloric acid
• What precipitate forms when sulfate ions are present in barium chloride solution?

  A white precipitate
• What can instrumental methods detect and identify?

  Elements and compounds
• What are the advantages of instrumental methods compared to chemical tests?

  They are accurate, sensitive, and rapid
• What is flame emission spectroscopy used for?

  To analyze metal ions in solutions
• What happens to the sample in flame emission spectroscopy?

  It is put into a flame
• What is produced when light is passed through a spectroscope in flame emission spectroscopy?

  A line spectrum
• What can be analyzed from the line spectrum produced in flame emission spectroscopy?

  The metal ions in the solution and their concentrations
• What are the steps to test for halides?

  1. Add dilute nitric acid
  2. Add silver nitrate solution
  3. Observe the precipitate:

  • Chloride: white precipitate
  • Bromide: cream precipitate
  • Iodide: yellow precipitate
• What are the steps to test for sulfates?

  1. Add dilute hydrochloric acid
  2. Add barium chloride solution
  3. Observe the precipitate:

  • White precipitate indicates sulfate ions
• What are the advantages of using instrumental methods for detection and identification?

  • Accurate
  • Sensitive
  • Rapid
  • More reliable than chemical tests
• What is the process of flame emission spectroscopy?

  1. Sample is placed in a flame
  2. Light emitted is passed through a spectroscope
  3. A line spectrum is produced for analysis
  4. Identifies metal ions and measures concentrations