Qualitative Analysis Flashcards
(22 cards)
Fe2+ + H2SO4 + KMnO4
Purple KMnO4 is decolourised.
MnO4- + 8H+ + 5Fe2+ –> Mn2+ + 5Fe3+ + 4H2O
Fe2+ oxidised, MnO4- reduced
Fe3+ and KI
Turns from orange(Fe3+) to brown.
2Fe3+ + 2I- –> 2Fe2+ + I2
Fe2+ ions very pale green so masked by formation of iodine.
Potassium dichromate, H2SO4, and zinc granules
Effervescence and solution turns from orange to green (in the presence of excess zinc this can then turn blue).
Cr2O7- + 14H+ + 3Zn –> 2Cr3+ + 7H2O + 3Zn2+
Cr2O72- reduced, Zn oxidised.
Copper sulfate and KI solution
Blue solution becomes a brown suspension and a white precipitate settles at the bottom of the test tube.
2Cu2+ + 4I- –> 2CuI + I2(s)
I- oxidised, Cu2+ reduced. White precipitate forms from Cu+ ions with I- ions forming copper(I) iodide
Cr3+ solution, NaOH, H2O2, and warm
Green solution initially forms a grey-green precipitate on addition of NaOH. This redissolves in excess NaOH to form a dark green solution. This turns yellow when H2O2 is added.
Copper (I) oxide + H2SO4 and warm
Colourless solution and a brown solid becomes a blue solution with a red-brown solid.
Cr3+ with 3-4 drops of NaOH and with excess NaOH
Dark green/blue solution goes to a grey-green precipitate. (3-4 drops)
Precipitate dissolves and a dark green solution. (excess)
Fe2+ with 3-4 drops of NaOH and with excess NaOH
Pale green solution goes to a pale green solution with a green precipitate. (3-4)
Dark green precipitate (excess)
Fe3+ with 3-4 drops of NaOH and with excess NaOH
Yellow solution goes to a brown precipitate in orange solution (3-4)
Orange precipitate in dark green solution (excess)
Cu2+ with 3-4 drops of NaOH and with excess NaOH
Blue solution goes to a blue solution with blue precipitate (3-4)
Blue solution with blue precipitate (excess)
Cr3+ with 3-4 drops of NH3 and with excess NH3
Dark green/blue solution goes to a grey-green ppt in a dark green solution. (3-4)
Cloudy dark green solution (excess)
Fe2+ with 3-4 drops of NH3 and with excess NH3
Pale green solution goes to pale yellow solution (3-4)
Dark green solution (excess)
Fe3+ with 3-4 drops of NH3 and with excess NH3
Yellow solution goes to orange solution (3-4)
Dark green solution with orange ppt (excess)
Cu2+ with 3-4 drops of NH3 and with excess NH3
Blue solution goes to blue solution with white precipitate (3-4)
Dark blue solution (excess)
Fe3+ with conc. HCl and then water
Yellow solution goes to bright yellow solution (HCl)
Returns to yellow solution (water)
Cu2+ with conc. HCl and then water
Blue solution goes to bright green solution (HCl)
Returns to blue solution (water)
Test for ammonium ions
Add NaOH solution, warm and test gas with damp pink litmus paper. Positive - litmus paper turn blue
NH4+ + OH- –> NH3+ + H2O
Test for carbonate ions (CO32-)
Add acid, eg. HNO3. Positive - bubbles of gas produced and turns limewater cloudy when bubbled through.
CO32- + 2H+ –> CO2 + H2O
Test for chloride ions
Add dilute nitric acid and silver nitrate solution - then add dilute NH3 followed by conc. NH3. Positive - white precipitate formed and redissolves after addition of dilute NH3.
Ag+ + Cl- –> AgCl
Test for bromide ions
Add dilute nitric acid and silver nitrate solution - then add dilute NH3 followed by conc. NH3.
Positive - cream ppt formed and redissolves in concentrated NH3.
Ag+ + Br- –> AgBr
Test for iodide ions
Add dilute nitric acid and silver nitrate solution - then add dilute NH3 followed by conc. NH3.
Positive - yellow ppt formed didn’t redissolve in either dilute or concentrated NH3.
Ag+ + I- –> AgI
Test for sulfate ions (SO42-)
Add nitric acid and barium nitrate solution. Positive - no change after adding acid, white ppt forms after adding barium ions.
Ba2+ + SO42- –> BaSO4
