Reactions of Ions in Aqueous Solution 3.2.6 Flashcards
How are metal-aqua complexes formed
When we add a transition metal compound to water
what are metal aqua ions in solution .
Acidic in solution
The charge of the ion has an effect on how acidic it is
What are 2 generic examples of acidity or hydrolysis reactions
[M(H2O)6]2+ + H2O (reverse sign) [M(H2O)5(OH)]+ + H3O+
[M(H2O)6]3+ + H2O (reverse sign) [M(H2O)5(OH)]2+ + H3O+
Why are [M(H2O)6] 3+ more acidic than [M(H2O)6] 2+
• +3 metal ions have a higher charge density than 2+ ions . This is because they have a larger charge and they’re small
• +3 metal ions are more polarising . This means that they attract electrons in the O-H bond in the water ligands more strongly
• This weakens O-H bond so it breaks more easily releasing H+ ions
Where does equilibrium lie when we add OH- ions to a hydrolysis reaction of metal aqua ions
If we add OH- they remove H3O+ and equilibrium shifts to the right
How can we hydrolyse a metal aqua ion further
Use OH- ions to make insoluble metal hydroxides
what are the equations on further hydrolysing a metal aqua ion using OH- to form a neutral complex that is solid and forms a precipitate in solution for +3 ions
Start from :
[M(H2O)6]3+ (aq) + H2O(l) (reverse sign) [M(H2O)5(OH)]2+ (aq) + H3O+ (aq)
Further hydrolysed to :
[M(H2O)5(OH)]2+ (aq) + H2O(l) (reverse sign) [M(H2O)4(OH)2]+ (aq) + H3O+ (aq)
Further hydrolysed to :
[M(H2O)4(OH)2]+ (aq) + H2O(l) (reverse sign) M(H2O)3(OH)3 (s) + H3O+ (aq)
what are the equations for further hydrolysis of metal aqua ions using OH- to form a neutral , insoluble solid complex from 2+ metal aqua ions
Start from :
[M(H2O)6]2+ (aq) +H2O(l) (reverse sign) [M(H2O)5(OH)]+ (aq) +H3O+ (aq)
further hydrolyse to :
[M(H2O)5(OH)]+ (aq) +H2O(l) (reverse sign) M(H2O)4(OH)2 (s) +H3O+ (aq)
what does amphoteric mean and what’s an example
Metal hydroxides can act as an acid or a base
what does it mean when metal hydroxides are amphoteric
Will dissolve in both excess acid and base
how can we reverse the reaction of amphoteric metal hydroxides precipitates
Add an acid (H+ ions) to the metal hydroxide precipitate and it will dissolve .
They do this by accepting a H+ ion and are bronsted lowry bases
what’s an example of an amphoteric metal hydroxide
Aluminium hydroxide Al(H2O)3(OH)3
what happens when we add a base to aluminium hydroxide (amphoteric molecule)
It acts as a bronsted lowry acid and donates H+ ions to react with the OH- and it dissolves
what’s the reaction of adding a base to aluminium hydroxide (amphoteric)
Al(H2O)3(OH)3 (s) + OH- (aq) => [Al(H2O)2(OH)4]- (aq) + H2O(aq)
what happens when we add an acid to aluminium hydroxide (amphoteric)
It acts as a bronsted lowry base by accepting H+ ions to form H3O+ in solution and dissolves
what’s the reaction of adding an acid to aluminium hydroxide (amphoteric )
Al(H2O)3(OH)3 (s) + 3H+ (aq) => [Al(H2O)6] 3+ (aq)
what happens when we add ammonia to metal aqua ions
They form metal hydroxide precipitates
what happens when we add excess ammonia to metal aqua ions
A ligand substitution reaction occurs
what’s the reaction of Cu(OH)2(H2O)4 when excess ammonia is added
Cu(OH)2(H2O)4(aq) + 4NH3(aq) (reverse sign) [Cu(NH3)4(H2O)2]2+ (aq) + 2OH-(aq) + 2H2O(l)
whats the reaction when you add a 2+ metal aqua ion complex with a small amount of ammonia
[M(H2O)6]2+ (aq) + 2NH3(aq) => M(H2O)4 (OH2) (s) + 2NH4+ (aq)
whats the reaction when you add a small amount of ammonia to a 3+ metal aqua complex
[M(H2O)6]3+ (aq) + 3NH3(aq) => Fe(H2O)3(OH)3 (s) + 3NH4+ (aq)
what happens when you add sodium carbonate to a 2+ metal aqua ion
forms metal carbonates precipitates
what’s the reaction of adding carbonates to a 2+ metal aqua ions
[M(H2O)6]2+ (aq) + CO3 2- (aq) (reverse sign) MCO3(s) + 6H2O(l)
what’s the reaction with carbonates and a 3+ metal aqua ions
2 [M(H2O)6]3+ (aq) + 3CO3 2- (aq) (reverse sign) 2M(OH)3(H2O)3 (s) + 3CO2 (g) + 3 H2O (l)
How do we perform test tube reactions to identify metal ion solutions
1) add a sample of the unknown metal ion solution into 3 test tubes
2) Drop by drop add NaOH to tube 1 and observe any changes .
Then add more to see if excess NaOH results in a further change .
3) Repeat step 2 except use ammonia solution in test tube 2
4) In tube 3 add sodium carbonate solution Na2CO3
what is the observation when you add NaOH and excess NaOH to aluminium hydroxide
Al3+ ions in solution + NaOH = Precipitate formed
Add excess NaOH = precipitate dissolves
what’s the observation when you add NH3 and NH3 in excess to copper hydroxide
Cu2+ ions in solution + NH3 = precipitate formed
Add excess NH3 = precipitate dissolves dark blue colour formed
What is the observation with Al3+ and Fe3+ (3+ metal ions) reacting with carbonates
Form a brown precipitate and carbon dioxide so bubbles will be observed
what’s the observation with Cu2+ and Fe2+ (2+ metal ions) reacting with carbonates
forms a green precipitate only
why do solutions of Fe2+ forming Fe3+ need to be made fresh
Because Fe2+ oxidises readily with air to form Fe3+
what’s the colour of Cu2+ in aqueous solution
Blue
what’s the colour when you add small amount of OH- or NH3 to aqueous solution of Cu2+
Pale blue precipitate
what’s the colour when you add excess NH3 to the precipitate of Cu2+
Dark blue solution
what’s the colour when you add Na2CO3 to Cu2+
Green blue precipitate
what’s the colour when you add excess OH- to the precipitate of Cu2+
Insoluble in excess NaOH
(no change )
what’s the colour of Fe2+ in aqueous solution
Pale green
what’s the colour of Fe3+ in aqueous solution
Yellow
what’s the colour of Al3+ in aqueous solution
Colourless
what’s the colour when you add small amount of OH- or NH3 to aqueous solution of Fe2+
Dirty Green precipitate
what’s the colour when you add small amount of OH- or NH3 to aqueous solution of Fe3+
Orange precipitate
what’s the colour when you add small amount of OH- or NH3 to aqueous solution of Al3+
White precipitate
what’s the colour when you add excess OH- to the precipitate of Fe2+
Insoluble in excess NaOH
(No change)
what’s the colour when you add excess OH- to the precipitate of Fe3+
Insoluble in excess NaOH
(No change)
what’s the colour when you add excess OH- to the precipitate of Al3+
Colourless solution
what’s the colour when you add excess NH3 to the precipitate of Fe2+
Insoluble in excess NH3
(No change)
what’s the colour when you add excess NH3 to the precipitate of Fe3+
Insoluble in excess NH3
(no change)
what’s the colour when you add excess NH3 to the precipitate of Al3+
No change
what’s the colour when you add Na2CO3 to Fe2+
Green precipitate
what’s the colour when you add Na2CO3 to Fe3+
Brown precipitate
what’s the colour when you add Na2CO3 to Al3+
white precipitate
EQ : suggest a reagent for the reaction from [Fe(H2O)6]3+ to [Fe(H2O)6]2+ (1)
Zn
