8.3 Qualitative analysis
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What does qualitative analysis rely on
Simple observations rather than measurements and can be carried out quickly on a test tube scale Observations may be gas bubbles, precipitates, colour changes or identification of gases
What is the test for carbonates
• Add dilute nitric acid to the solid or solution to be tested • If you see bubbles, the unknown compound could be a carbonate. • To prove that the gas is carbon dioxide, bubble the gas through calcium hydroxide solution, a white precipitate forms which turns the lime water cloudy
What is the test for sulfates
Aqueous barium ions are added to a solution of an unknown compound Usually in barium chloride or nitrate, use nitrate if you want to do a halide test after
What is the test for halides
Most are soluble in water but silver halides are insoluble Aqueous silver ions react with aqueous halide ions to form precipitates of silver halides as shown by the general equation Ag+(aq) + X-(aq) -> AgX(s) Add silver nitrate, silver halide precipitates different colours, add aqueous ammonia to test the solubility of the precipitate
What colours does a solution turn if a halide is present
Chloride - white Bromide - Cream Iodide - yellow
What is the correct order to test for anions
Carbonate Sulfate Halides
What are barium meals used for
Enable doctors to see the outline of the gllet, stomach and upper small intestine in order to identify abnormalities such as ulcers or tumors
What is the test for ammonium ions
Aqueous sodium hydroxide is added to a solution Ammonia gas is produced, unlikely to see bubbles as ammonia is very soluble in water May be able to smell, test with moist pH indicator paper. Ammonia is alkaline so paper will turn blue