5.11 - Tests and Observations in Inorganic Chemistry

• qualitative analysis

  answers question 'what is it?' through careful observations during test tube experiments and flame tests
• changes observed in qualitative analysis 


  gas bubbling off

  different smells

  precipitates forming

  solids dissolving

  temperatures changing

  new colours appearing
• use of ionic precipitate reactions

  test for anions
• adding silver nitrate solution to a halide

  produces a precipitate that can be used to distinguish between chloride, bromides and iodides
• adding soluble salt to a sulfate solution

  produces a white precipitate of insoluble barium sulfate
• hydrochloric acid + carbonate

  adds hydrogen ions to carbonate ions turning them into carbonic acid molecules (H2CO3) which decomposes into carbonate dioxide and water

  test with limewater to show carbon dioxide is produced
• sodium hydroxide use

  test for ammonium ions in salts like ammonium chloride
• testing for ammonium using sodium hydroxide

  warming ammonium salt with sodium hydroxide solution produces alkaline gas with a pungent smell - ammonia

  ammonia is formed when OH‐ removes H+ from ammonium ions
• common oxidising agents in inorganic tests

  chlorine

  bromine

  acidic solutions of iron (iii) ions, manganate (vii) ions or dichromate (vi) ions
• reagents useful for detecting oxidising agents

  reagents that change colour when oxidised
• example of reagent that changes colour when oxidised

  colourless solution of iodide ions turns yellow-brown when oxidised

  can be a sensitive test for starch

  oxidation of iodide ions by chlorine or bromine is a redox reaction where one halogen displaces another
• common inorganic reducing agents

  metals (in presence of acid or alkali)

  sulfur dioxide

  iron (ii) ions
• reagent that changes colour when reduced

  dichromate (vi) ions in acid change from orange to green

  basis of a test for sulfur dioxide gas