R.P 11 (Transition metal ion tests) Flashcards
What do limited NH3 and OH- act as when they reacts with aqueous metal ions
NH3 and OH- ions are acting as
Bronsted-Lowry bases accepting a proton
The bases OH- and ammonia when in limited
amounts form the same hydroxide precipitates
Write the equation for when aqueous cu2+ reacts with limited OH- and NH3
State the colour the precipitate formed
[Cu(H2O)6]2+(aq) + 2OH- (aq) —> Cu(H2O)4(OH)2 (s) +2H2O (l)
[Cu(H2O)6]2+(aq) + 2NH3 (aq) —> Cu(H2O)4(OH)2 (s) +2NH4+ (aq)
Blue precipitate
Write the equation for when aqueous Fe2+ reacts with limited OH- and NH3
State the colour the precipitate formed
[Fe(H2O)6]2+(aq) + 2OH- (aq) —> Fe(H2O)4(OH)2 (s) +2H2O (l)
[Fe(H2O)6]2+(aq) + 2NH3 (aq) —> Fe(H2O)4(OH)2 (s) +2NH4+ (aq)
Green precipitate
Write the equation for when aqueous Al3+ reacts with limited OH- and NH3
State the colour the precipitate formed
[Al(H2O)6]3+(aq) + 3OH-(aq) —-> Al(H2O)3(OH)3 (s) +3H2O (l)
[Al(H2O)6]3+(aq) + 3NH3(aq) —-> Al(H2O)3(OH)3 (s) +3NH4+ (aq)
White precipitate
Write the equation for when aqueous Fe3+ reacts with limited OH- and NH3
State the colour the precipitate formed
[Fe(H2O)6]3+(aq) + 3OH-(aq) —-> Fe(H2O)3(OH)3 (s) +3H2O (l)
[Fe(H2O)6]3+(aq) + 3NH3(aq) —-> Fe(H2O)3(OH)3 (s) +3NH4+ (aq)
Brown precipitate
What are the practical steps when adding OH- to test for aqueous metal ions
Method sodium hydroxide
a) Place about 10 drops of metal ion solution in a test
tube.
b) Add sodium hydroxide solution, dropwise with gentle
shaking, until in excess.
What are the practical steps when adding NH3 to test for aqueous metal ions
Method ammonia solution
a) Place about 10 drops of metal ion solution in a
test tube.
b) Add ammonia solution, dropwise with gentle
shaking, until in excess.
What is the only aqueous metal ion which forms a precipitate that dissolves in XS OH-
Write an equation for the 2 steps in this reaction
State what is observed
Al3+
[Al(H2O)6]3+(aq) + 3OH-(aq) —-> Al(H2O)3(OH)3 (s) +3H2O (l)
Al(H2O)3(OH)3 (s) + OH-(aq ) —> [Al(OH)4]-(aq) + 3H2O (l)
White ppt to colourless solution
What is the only aqueous metal ion which forms a precipitate that dissolves in XS NH3
Write an equation for the 2 steps in this reaction
State what is observed
Cu2+
Partial ligand substitution
[Cu(H2O)6]2+(aq) + 2NH3 (aq) —> Cu(H2O)4(OH)2 (s) +2NH4+ (aq)
Cu(OH)2(H2O)4(s) + 4NH3 (aq) —–> [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O (l) + 2OH-(aq)
Blue ppt to dark blue solution
What are the practical steps in using sodium carbonate to test for aqueous metal ions
Method sodium carbonate
a) Place about 10 drops of sodium carbonate solution in a test tube.
b) Add about 10 drops of metal ions solution and shake the mixture gently
Write an equation for the reaction between aqueous Cu2+ with sodium carbonate
State what type of reaction this is
State what is observed
Precipitation reaction
[Cu(H2O)6]2+ + CO32- —-> CuCO3 + 6H2O
Blue/green ppt
Write an equation for the reaction between aqueous Fe2+ with sodium carbonate
State what type of reaction this is
State what is observed
Precipitation reaction
[Fe(H2O)6]2+ + CO32- —-> FeCO3 + 6H2O
Green ppt
Write an equation for the reaction between aqueous Fe3+ with sodium carbonate
State what type of reaction this is
State what is observed
Acidity reaction
2[Fe(H2O)6]3+(aq) + 3CO32-(aq) —-> 2Fe(OH)3(H2O)3(s) +3CO2 + 3H2O(l)
Brown ppt
Write an equation for the reaction between aqueous Al3+ with sodium carbonate
State what type of reaction this is
State what is observed
Acidity reaction
2[Al(H2O)6]3+(aq) + 3CO32-(aq) —-> 2Al(OH)3(H2O)3(s) +3CO2 + 3H2O(l)
White ppt
Why is a carbonate produced when NaCO3 reacts with 2+ ions but not 3+ ions
The difference is explained by the
greater polarising power of the 3+ ion due to its higher charge density.
