8.3 Qualitative Analysis
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What are qualitative tests?
results are OBSERVATIONS rather than numerical values.
What are the 3 molecules being tested for?
CARBONATES (CO32-) SULPHATES (SO42-) HALIDES (X-)
What is the test for carbonates?
carbonate + ACID ⟶ salt + carbon dioxide acid should not be HCl or H2SO4 if later carrying out test for halides/sulfates.
During the carbonate test, a positive result is when bubbles of carbon dioxide gas is produced. How can you test this gas to confirm it is CO2?
bubble through limewater, (aqueous Ca(OH)2) should turn cloudy. (formation of CaCO3 white precipitate)
What is the equation for when carbon dioxide is bubbled through limewater?
CO2 (g) + Ca(OH)2 (aq) ⟶ CaCO3 (s) + H2O (l)
What does limewater consist of?
aqueous Calcium Hydroxide, Ca(OH)2
What product is formed as a white precipitate during the LIMEWATER test which makes the solution cloudy?
CaCO3, calcium carbonate
What is the test for sulphates?
Sulphate + BARIUM NITRATE (Ba(NO3)2) ⟶ Barium sulfate (BaSO4) BaSO4 white precipitate formed. Barium compound should not be barium chloride if halide test being carried out after.
What is the product is formed as a white precipitate during the SULFATE test?
BaSO4, barium sulphate
What is the test for halides?
Halide + AgNO3, SILVER NITRATE ⟶ coloured halide precipitate
What different coloured precipitates form for each halide?
chloride - white bromide - cream iodide - yellow
How can you determine the presence of a silver halide using solubility?
add AQUEOUS AMMONIA to silver halide. AgCl dissolves in dilute ammonia AgBr dissolves in concentrated ammonia AgI insoluble in even concentrated ammonia