Tests for ions

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C7.10 Precipitation reactions and tests for ions
Compounds containing a metal or ammonium in the name are ionic.  These compounds contain ions which can be worked out from the name.  Eg. aluminium sulfate contains an aluminium Al3+ and sulfate ions SO42-.

ion name ion formula  example compound with ion
hydrogen H+ any acid e.g. hydrochloric acid HCl
sodium Na+ sodium bromide NaBr
potassium K+ potassium iodide KI
aluminium Al3+ aluminium sulfate Al2(SO4)3
calcium Ca2+ calcium sulfate CaSO4
copper Cu2+ copper sulfate CuSO4
iron II Fe2+ iron II sulfate FeSO4
iron III Fe3+ iron III sulfate Fe2(SO4)3
ammonium NH4+ ammonium chloride NH4Cl
carbonate CO32- potassium carbonate K2CO3
sulfite SO32- calcium sulfite CaSO3
sulfate SO42- magnesium sulfate MgSO4
chloride Cl- lead chloride PbCl2
bromide Br- silver bromide AgBr
iodide I- sodium iodide NaI
hydroxide OH- sodium hydroxide NaOH

If any of the above ions that can combine to make an insoluble compound are present in a mixture of ionic compounds in solution then they will do so.  The result will be the formation of a precipitate.  e.g. You can work out that iron II hydroxide is insoluble and that iron II sulfate and sodium hydroxide are soluble.  When mixed that following ions are present; iron II, hydroxide, sulfate, and sodium.  The result will be a precipitate of iron II hydroxide.
learning activity - name both of the ions in each of the compounds in the table above.
list the soluble and insoluble compounds in the table
name pairs of soluble compounds from the table and name the precipitate formed


C7.11
Tests for common ions

name of ion test result of positive test
hydrogen add universal indicator Photo_050905_003.jpg (62347 bytes) indicator turns red Photo_050905_004.jpg (53069 bytes)
hydrogen add carbonate effervescence 
carbon dioxide detected
hydrogen add magnesium  mgtohcl.JPG (59599 bytes) effervescence hydrogen detected hionhtest.JPG (65663 bytes)
sodium flame test  yellow flame Photo_050905_005.jpg (60261 bytes)
potassium flame test lilac flame Photo_050905_006.jpg (57778 bytes)
calcium flame test brick red flame 
copper flame test blue/green flame Photo_050905_007.jpg (58669 bytes)
aluminium add drop aqueous sodium hydroxide
add excess  aqueous sodium hydroxide
white precipitate forms
white precipitate redissolves
calcium add drop aqueous sodium hydroxide
add excess  aqueous sodium hydroxide
fine white precipitate forms
precipitate does not dissolve
copper add drop aqueous sodium hydroxide blue precipitate form
iron II add drop aqueous sodium hydroxide green precipitate forms
iron III add drop aqueous sodium hydroxide iron3.JPG (48102 bytes) brown precipitate forms brownppt.JPG (53897 bytes)
ammonium add 5cm3 of sodium hydroxide and warm ammonia detected
carbonate add a little dilute acid effervescence
carbon dioxide detected
sulfite add a little dilute hydrochloric acid, warm sulfur dioxide detected
sulfate add dilute hydrochloric acid then a few drops of aqueous barium chloride sulfateions.JPG (68892 bytes) white precipitate formed bappt.JPG (68919 bytes)
chloride add dilute nitric acid then a few drops of silver nitrate hno3cl.JPG (55965 bytes) white precipitate forms agclppt.JPG (56173 bytes)
bromide add dilute nitric acid then a few drops of silver nitrate buff precipitate forms
iodide add dilute nitric acid then a few drops of silver nitrate yellow precipitate form
hydroxide add universal indicator ohphpap.JPG (59761 bytes) indicator turns blue phpapblue.JPG (54536 bytes)
hydroxide add ammonium compound and warm ammonia detected

What would you see with named compounds and named reagents?
Identify X if Y seen with reagent Z
How would you test compound X?


C7.12 explaining ion tests with equations
hydrogen ions
hydrochloric acid + magnesium ---> magnesium chloride + hydrogen
2HCl(aq) + Mg(s) ---> MgCl2(aq) + H2(aq)
2H+(aq) + Mg(s) ---> Mg2+(aq) + H2(g)
nitric acid + sodium carbonate --> sodium nitrate + water + carbon dioxide
2HNO3(aq) + Na2CO3(aq) ---> 2NaNO3(aq) +H2O(l) + CO2(g)
2H+(aq) + CO32-(aq) ---> H2O(l) + CO2(g)
Aluminium ions
aluminium sulfate + sodium hydroxide ---> aluminium hydroxide + sodium sulfate
Al2(SO4)3(aq) + 6NaOH(aq) ---> 2Al(OH)3(s) + 3Na2SO4(aq)
2Al3+(aq) + 6OH- ---> 2Al(OH)3(s)
aluminium hydroxide + sodium hydroxide ---> sodium aluminate
Al(OH)3(s) + NaOH(aq) ---> NaAl(OH)4(aq)
Al(OH)3(s) + OH-(aq) ---> Al(OH)4-(aq)
calcium ions
calcium nitrate + sodium hydroxide ---> calcium hydroxide + sodium nitrate
Ca(NO3)2(aq) + 2NaOH(aq) ---> Ca(OH)2(s) + 2NaNO3(aq)
Ca2+(aq) + 2OH-(aq) ---> Ca(OH)2(s)
copper ions
copper chloride + sodium hydroxide ---> copper hydroxide + sodium chloride
CuCl2(aq) + NaOH(aq) ---> Cu(OH)2(s) + NaCl(aq)
Cu2+(aq) + OH-(aq) ---> Cu(OH)2(s)
iron II ions
iron II chloride + sodium hydroxide ---> iron II hydroxide + sodium chloride
FeCl2(aq) + NaOH(aq) ---> Fe(OH)2(s) + NaCl(aq)
Fe2+(aq) + OH-(aq) ---> Fe(OH)2(s)
iron III ions
iron III sulfate + sodium hydroxide ---> iron III sulfate + sodium sulfate
Fe2(SO4)3(aq) + 6NaOH(aq) ---> 2Fe(OH)3(aq) + 3Na2SO4(aq)
Fe3+(aq) + 3OH-(aq) ---> Fe(OH)3(aq)
ammonium ions or hydroxide ions
ammonium chloride + sodium hydroxide ---> sodium chloride + water + ammonia
NH4Cl(aq) + NaOH(aq) ---> NaCl(aq) + H2O(l) + NH3(g)
NH4+(aq) + OH-(aq) ---> H2O(l) + NH3(g)
carbonate ions
sodium carbonate + nitric acid --->sodium nitrate + water + carbon dioxide
Na2CO3(aq) + 2HNO3(aq) ---> 2NaNO3(aq) + H2O(aq) + CO2(aq)
CO32-(aq) + 2H+(aq) --- > H2O(aq) + CO2(aq)
sulfite
sodium sulfite + hydrochloric acid ---> sodium chloride + water + sulfur dioxide
Na2SO3(aq) + 2HCl ---> 2NaCl(aq) + H2O(aq) + SO2(aq)
SO32-(aq) + 2H+(aq) --->  H2O(aq) + SO2(aq)
sulfate
sodium sulfate + barium chloride ---> barium sulfate + sodium chloride
Na2SO4(aq) + BaCl2(aq) ---> BaSO4(s) + 2NaCl(aq)
SO42-(aq) + Ba2+(aq) ---> BaSO4(s)
chloride
sodium chloride + silver nitrate ---> silver chloride + sodium nitrate
NaCl(aq) + AgNO3(aq) ---> AgCl(s) + NaNO3(aq)
Cl-(aq) + Ag+(aq) ---> AgCl(s)
bromide
sodium bromide + silver nitrate ---> silver bromide + sodium nitrate
NaBr(aq) + AgNO3(aq) ---> AgBr(s) + NaNO3(aq)
Br-(aq) + Ag+(aq) ---> AgBr(s)
iodide
sodium iodide + silver nitrate ---> silver iodide + sodium nitrate
NaI(aq) + AgNO3(aq) ---> AgI(s) + NaNO3(aq)
I-(aq) + Ag+(aq) ---> AgI(s)