Chemical Analysis: Identification of Ions Flashcards
potassium ions
K+
what colour flame do potassium ions produce?
lilac
copper ions
Cu2+
what colour flame do copper 2+ ions produce?
green
sodium ions
Na+
what colour flame do sodium ions produce?
yellow
calcium ions
Ca2+
what colour flame do calcium ions produce?
orange-red flame
lithium ions
Li+
what colour flame do lithium ions produce?
crimson
why are flame tests used?
to identify metal ions in ionic compounds
flame test practical steps
- submerge nichrome wire loop in dilute HCl to clean it
- place nichrome wire into sample being tested
- hold nichrome wire loop in bunsen burner’s blue flame
- observe change in colour of bunsen burner flame
what colour precipitate do magnesium ions (Mg2+) form?
white precipitate magnesium hydroxide
magnesium hydroxide equation
Mg2+ (aq) + 2OH- (aq) –> Mg(OH)2 (s)
what colour precipitate do aluminium ions (Al3+) form?
white precipitate aluminium hydroxide
aluminium hydroxide equation
Al3+ (aq) + 3OH- (aq) –> Al(OH)3 (s)
what does aluminium hydroxide dissolve in?
excess NaOH (forms colourless solutions)
what colour precipitate do calcium ions (Ca2+) form?
white precipitate calcium hydroxide
calcium hydroxide equation
Ca2+ (aq) + 2OH- (aq) –> Ca(OH)2 (s)
what colour precipitate do iron ions (Fe2+) form?
green precipitate iron (II) hydroxide
iron (II) hydroxide equation
Fe2+ (aq) + 2OH- (aq) –> Fe(OH)2 (s)
what colour precipitate do iron ions (Fe3+) from?
brown precipitate iron (II) hydroxide
iron (III) hydroxide equation
Fe3+ (aq) + 3OH- (aq) –> Fe(OH)3 (s)
what colour precipitate do copper ions (Cu2+) form?
blue precipitate copper (II) hydroxide
copper (II) hydroxide equation
Cu2+ (aq) + 2OH- (aq) –> Cu(OH)2 (s)
Test for carbonates?
- add dilute acid to sample
- CO2 will be produced, observed by effervescence
- bubble gas through limewater to test it
what do all carbonates produce?
CO3 2-
how to test for halides?
- add dilute nitric acid to unknown solution (removes carbonate ions to ensure they don’t form a precipitate)
- add dilute silver nitrate
- if halide ions are present, they will form a white precipitate with silver ions
what colour precipitate is silver chloride?
white
silver chloride equation
Ag+ (aq) + Cl- (aq) –> AgCl (s)
what colour precipitate is silver bromide?
cream
silver bromide equation
Ag+ (aq) + Br- (aq) –> AgBr (s)
what colour precipitate is silver iodide?
pale yellow
silver iodide equation
Ag+ (aq) + I- (aq) –> AgI (s)
how to test for sulfates?
- add dilute HCl to unknown sample (removes carbonate ions which could disrupt results by forming a precipitate)
- add barium chloride solution
- white precipitate forms if sulfates are present
what colour precipitate does barium sulphate form?
white
barium sulphate equation
Ba2+ (aq) + SO4 2- (aq) –> BaSO4 (s)
advantages of using instrumental methods of chemical analysis
greater sensitivity and accuracy
- quicker at producing results
- able to analyse tiny samples
disadvantages of using instrumental methods of chemical analysis
- expensive
- must go through special training to operate the instruments
- only useful when compared to data from known substances
how does flame emission spectroscopy work?
- place sample of metal solution being tested into a flame, light will be given off
- light given off is captured in a spectroscope - instrument generates a line spectrum by distinguishing between light with different wave lengths
what does a flame emission spectroscopy analyse?
- identity of metal ions (metal ions generate new lines on spectrum so can identify all ions present in solution)
- concentration of metal ions (intensity of line)
- reference spectra (analyse mixtures by comparing them with reference spectra)
