qualitative analysis: ion tests Flashcards
define qualitative analysis
indicates whether a particular species is present or not
define precipitate
an insoluble solid formed when two solutions are mixed together
test for carbonate ions
add dilute aqueous acid (HNO3) tot the solution
fizzing due to the carbon dioxide gas produced
how to identify carbon dioxide
gas can be tested using limewater which would produce a white precipitate
ionic equation for carbonate
CO3 2- (aq) + 2H+ (aq) —> H2O (l) CO2 (g)
test for sulfate ions
add dilute nitric acid, HNO3, followed by barium nitrate solution, Ba(NO3)2
white precipitate forms - insoluble barium sulfate
ionic equation for sulfate
Ba 2+ (aq) + SO4 2- (aq) —> BaSO4 (s)
test for halides
ad dilute nitric acid, HNO3, followed by aqueous silver nitrate solution, AgNO3 to the solution
look for a whit/cream/yellow precipitate - insoluble silver halide
ionic equation for halide
Ag+ (aq) + X- (aq) —>AgX (s)
how to decipher between halides
add aqueous ammonia solution, NH3 can distinguish between each one on the basis of solubility
Cl- = precipitate dissolves in both dilute and concentrated ammonia solution to form a colorless solution
Br- = precipitate does not dissolve in dilute ammonia solution but does dissolve in concentrated ammonia solution to form a colorless solution
I- =precipitate does not dissolve in dilute or concentrated solution
test for ammonium ions
add warm dilute aqueous sodium hydroxide, NaOH to the solution
ammonia gas will be produced when the solution is warmed
the ammonia can be detected with moist Ph indicator paper (turns blue)
ionic equation for ammonia
NH4+ (aq) + OH- (aq) —> NH3 (g) + H2O (l)
how could you distinguish between NaCl (s) NaBr (s) and NaI (s)
add water to dissolve the solids and produce aqueous ions
add dilute nitric acid
add silver nitrate solution, AgNO3 (aq)
note the color of the precipitate
then add dilute ammonia solution
if the precipitate does not dissolve, add concentrated ammonia solution
white precipitate that dissolves in dilute ammonia - NaCl
cream precipitate that does not dissolve in dilute ammonia, but dissolves in concentrated ammonia - NaBr
yellow precipitate that does not dissolve in dilute or concentrated ammonia - NaI
explain why it is important to carry out the carbonate test before carrying out the sulfate test on an unknown chemical
carbonate ions also give a white precipitate with barium nitrate
barium carbonate is insoluble in water
explain why if you are testing a mixture it is important to use dilute nitric acid rather than sulfuric acid or hydrochloric acid for the carbonate test
sulfuric acid contains sulfate ions which would give a white precipitate with barium nitrate
hydrochloric acid contains chloride ions which would give a white precipitate with silver nitrate
