qualitative analysis

• in a carbonate test you add dilute nitric acid / HNO3 (aq)
• positive result for carbonate test

  bubbles or effervescence
• carbonate test: proving the gas is CO2

  1. bubble gas through lime water - an aqueous solution of Ca(OH)2
  2. CO2 reacts to form a white ppt. of CaCO3 which turns it cloudy
• Na2CO3 (aq) + 2HNO3 (aq) -> 2NaNO3 (aq) + CO2 (g) + H2O (l)
• in a sulfate test you add barium ions (usually barium chloride or nitrate) to the sample
• a positive result for the sulfate test is the formation of a white ppt. of barium sulfate
• ionic equation for barium ions and sulfate:

  Ba 2+ (aq) + SO4 2- (aq) -> BaSO4
• if you intend to do a halide test after a sulfate test do not use barium chloride
• halide test:

  1. add aqueous silver nitrate
  2. add aqueous ammonia to tell halides apart
• halide positive results:

  • AgCl = white ppt.
  • AgBr = cream ppt.
  • AgI = yellow ppt.
• Cl- is soluble in dilute ammonia
• Br- is soluble in concentrated ammonia
• Iodide is insoluble in ammonia
• these are all tests for anions
• sequence of tests:

  1. carbonate test
  2. sulfate test
  3. halide test