tests for ions FINISH WITH NOTES Flashcards
Give a test for halide ions
React with acidified silver nitrate solution. Forms a coloured ppt
Ag+ (aq) + X- (aq) —> AgX(s)
Write the precipitate colours for halide tests
AgCl – white, AgBr – off-white/cream, AgI – yellow
Note AgF is soluble and does not produce a ppt
Explain how ammonia solution can be used to distinguish between
silver halide precipitates
Add ammonia
AgCl – dissolves, AgBr- dissolves when excess NH 3 is added, AgI – insoluble in NH 3
Explain why silver nitrate solution must be acidified when used to
test for halide ions
Prevents the formation of silver carbonate (Ag2CO3 )
This forms as a result of atmospheric CO2 dissolving in the solution
Give a test for ammonium ions
Warm with NaOH solution. Produces a basic gas (NH 3 )
Test with damp red litmus that turns blue
NH4+ (aq) + OH- (aq) —-> NH3 (g) + H2O(l)
Give a test for carbonate ions
Add HCl, H 2 SO 4 or HNO 3 . Test gas evolved with limewater (forms white ppt due to CO 2 )
2H + (aq) + CO32- (aq) —> H2O(l) + CO2 (g)
Test for hydroxide ions
Add a solution of Mg 2+ ions (e.g. MgCl 2 (aq)) forms white ppt of Mg(OH) 2
Mg2+ (aq) + 2OH- (aq) —> Mg(OH) 2 (s)
Give a test for sulfate ions
Add acidified barium chloride solution. White ppt of BaSO4 is formed
Ba2+ (aq) + SO42- (aq) —> BaSO4 (s)
Explain why barium chloride solution used to test for sulfate ions
must be acidified
Prevents the formation of a white ppt of BaCO3
This is formed when atmospheric CO 2 dissolves in the solution
Explain why acidified barium chloride or acidified silver nitrate
solution react with carbonate ions
Both solutions contain acid that reacts with the carbonate ions to produce CO 2 gas
2H+ (aq) + CO32- (aq) —-> H2O(l) + CO2 (g)
Give two sources of aqueous sulfate ions
Solutions of group 1 sulfate salts (Na2SO4 in solution produces SO4 - (aq) ions)
sulfuric acid (H2SO4 contains some SO42- ions)
Give the first step to test any unknown inorganic solid
dissolve in distilled water
