Test for Cations and Anions Sample Essay

CATION TEST OBSERVATION Copper Cu2+ Add dilute Na hydroxide solution e. g. in CuCl2 solution or solid. Blue precipitate of Cu hydrated oxide. which does non fade out in extra NaOH. Blue in solution or as a solid. CuSO4 ( aq ) + 2NaOH ( aq ) ( Cu ( OH ) 2 ( s ) + Na2SO4 ( aq ) Or Cu2+ + 2OH- ( Cu ( OH ) 2 ( s ) Iron ( II ) Fe2+ Add dilute Na hydroxide solution e. g. in FeCl2 solution or as a solid. Often pale green A dark green gelatinlike precipitate is formed that does non fade out in extra NaOH. in coloring material. It turns brown on standing as it is oxidised in air to Fe ( III ) hydrated oxide. Fe ( OH ) 3. FeCl2 ( aq ) + 2NaOH ( aq ) ( Fe ( OH ) 2 ( s ) + 2NaCl ( aq ) Or Fe2+ + 2OH- ( Fe ( OH ) 2 ( s ) Iron ( III ) Fe3+ Add dilute Na hydroxide solution e. g. in FeCl3 solution or solid ; frequently yellow in A dark rusty brown gelatinlike precipitate is formed that does non fade out in extra NaOH solution and red/brown in solid. FeCl3 ( aq ) + 3NaOH ( aq ) ( Fe ( OH ) 3 ( s ) + 3NaCl ( aq ) Or Fe3+ + 3OH- ( Fe ( OH ) 3 ( s )

Aluminium Al3+ Add dilute Na hydroxide solution These are colourless in solids and in solution A white precipitate signifiers. BUT it dissolves in extra Na hydroxide solution. because NaAl ( OH ) 4 ( aq ) is soluble. Aluminium hydrated oxide is said to be amphiprotic because it dissolves in an base and an acid AlCl3 ( aq ) + 3NaOH ( aq ) ( Al ( OH ) 3 ( s ) + 3NaCl ( aq ) Al ( OH ) 3 ( s ) + NaOH ( aq ) ( NaAl ( OH ) 4 ( aq ) Ammonium NH4+ Add dilute Na hydroxide solution NH4Cl and warm. trial gas with pH paper A smelly alkaline gas that turns pH paper blue is given off. Ammonia is released from the ammonium salt. ( NH4 ) 2SO4 + 2NaOH ( aq ) ( 2NH3 ( g ) + 2H2O + Na2SO4 ( aq ) or NH4+ ( aq ) + OH- ( NH3 ( g ) + H2O

Trials for Cations and Anions with Equations

ANION TEST OBSERVATION Carbonate CO32- Add dilute azotic acid e. g. in Na2CO3 in solution or as a solid Solid or the solution evolves a colourless gas which turns lime H2O milky – a white precipitate Na2CO3 ( s ) + 2HNO3 ( 2NaNO3 + CO2 + H2O Ca ( OH ) 2 ( aq ) + CO2 ( CaCO3 ( s ) + H2O Sulphate ion SO42- Add dilute hydrochloric acid to the Substance must be in solution solution. followed by Ba chlorideA white precipitate of Ba sulfate signifiers e. g. Na2SO4 ( aq ) solution BaCl2 ( aq ) + Na2SO4 ( aq ) ( BaSO4 ( s ) + 2NaCl ( aq ) Ionically Ba2+ ( aq ) + SO42- ( aq ) ( BaSO4 ( s ) Halide ions Add dilute azotic acid to the Chloride ion Cl – solution. so add silver nitrate Silver chloride is white. Ag bromide is cream. Ag iodide is xanthous. Bromide ion Br – solution ; observe the coloring material. Add You can separate between a chloride. bromide and iodide utilizing aqueous ammonia solution: Iodide ion I – ammonia solution and justice the AgCl is soluble in ammonia solution e. g. from KCl ( aq ) . NaBr ( aq ) . LiI ( aq ) solubility of the solid in it. AgBr is partly soluble AgI is indissoluble in NH3 ( aq ) AgNO3 ( aq ) + KCl ( aq ) ( AgCl ( s ) + KNO3 ( aq ) Ionically for an iodide ( I- ) Ag+ ( aq ) + I- ( AgI ( s )