3.2.6 ions in aqeuous solution (transition metal wth??)
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1
What are aqua ions?
When solid metal salts are dissolved in water:
FeCl3 + H2O --> [FE(H2O)6]$^{3+}$ + 3CL when 6 h2o are surrounding its called hexaqua ion
[FE(H2O)6]$^{2+}$ = GREEN
[FE(H2O)6]$^{3+}$ = YELLOW
[Cu(H2O)6]$^{2+}$ = BLUE
[Al(H2O)6]$^{3+}$ = COLOURLESS
FeCl3 + H2O --> [FE(H2O)6]$^{3+}$ + 3CL when 6 h2o are surrounding its called hexaqua ion
[FE(H2O)6]$^{2+}$ = GREEN
[FE(H2O)6]$^{3+}$ = YELLOW
[Cu(H2O)6]$^{2+}$ = BLUE
[Al(H2O)6]$^{3+}$ = COLOURLESS
2
Aciditiy of aqua ions?
Theyre weak acids but 3+ AQUA IONS are MORE ACIDIC then 2+ because it has a higher charge density so it polarises more the H20 group weakening the O-H bond so H+ lost more easily.
3+ aqua ions pH = around 3
2+ aqua ions pH = around 6
3+ aqua ions pH = around 3
2+ aqua ions pH = around 6
3
Sodium hdryxoide reaction with metal salt?
Reagent: NaOH(KOH) with OH- acting as base:
When NaOH is added the OH- reacts with the H+ aqua ions lost to make H20 and forms a neutral hydroxide precipitate.
eg for 2+ aqua ions: M(H2O)6]$^{2+}$ + 2OH --> M(H2O)4(OH)2 + 2H20 NO CHARGE
eg for 3+ aqaua ions M(H2O)6$^{3+}$ + 3OH --> M(H20)3(OH)3 +3H20 NEEDS EXTRA OH TO NEUTRALISE charge
When NaOH is added the OH- reacts with the H+ aqua ions lost to make H20 and forms a neutral hydroxide precipitate.
eg for 2+ aqua ions: M(H2O)6]$^{2+}$ + 2OH --> M(H2O)4(OH)2 + 2H20 NO CHARGE
eg for 3+ aqaua ions M(H2O)6$^{3+}$ + 3OH --> M(H20)3(OH)3 +3H20 NEEDS EXTRA OH TO NEUTRALISE charge
4
Precipitate colours formed when react with naoh?
Fe2+ = green pt
Cu2+ =blue pt
Fe3+ = BROWN pt
Al3+ = white pt
Cu2+ =blue pt
Fe3+ = BROWN pt
Al3+ = white pt
5
What happeneds if excess naoh is added?
Nothing changes apart for Aluminium due to its amphoteric features CAUSES IT TO LOSE ANOTHER H
If excess:
[Al(H2O)6]$^{3+}$ + 4OH- --> [Al(H20)2(OH)4]$^{-}$ + 4H20
THIS CAUSES PT TO DISSOLVE
If excess:
[Al(H2O)6]$^{3+}$ + 4OH- --> [Al(H20)2(OH)4]$^{-}$ + 4H20
THIS CAUSES PT TO DISSOLVE
6
Hydrolysis?
As theyre weak acids when dissolved in water they donate a H+ to H2O:
for +2 : [M(H2O)6]$^{2+}$ + H2O <--> [M(H2O)5OH]$^{+}$ + H30$^{+}$
for +3 its same except charge 3+ to 2+
NOTE THESE REACTIONS ARE REVERSIBLE
for +2 : [M(H2O)6]$^{2+}$ + H2O <--> [M(H2O)5OH]$^{+}$ + H30$^{+}$
for +3 its same except charge 3+ to 2+
NOTE THESE REACTIONS ARE REVERSIBLE
7
Ammonia with metal salt?(NOT EXCESS)
Ammonia can be used INSTEAD OF NaOH even if it is weaker base
Literally forms the same products apart from it forms NH4 then H2O
Literally forms the same products apart from it forms NH4 then H2O
8
Excess ammonia special
When excess with Co and Cu it acts as a LIGAND:
Cu = [Cu(H2O)6]$^{2+}$ + 4NH3 --> [Cu(NH3)4(H20)2]$^{2+}$ + 4H20 goes from blue to deep blue
For Cobalt NH3 replaces all 6 H20
Cu = [Cu(H2O)6]$^{2+}$ + 4NH3 --> [Cu(NH3)4(H20)2]$^{2+}$ + 4H20 goes from blue to deep blue
For Cobalt NH3 replaces all 6 H20
9
Sodium carbonate reaction with metal salt?
CO3$^2-$ is a weak base so with M$^{2+}$ it cant take the H+ so CO3- just reacts with metal directly:
M(H2O)6$^{2+}$ + CO$^{2-}$3 --> MCO3 + 6H2O
But With M$^{3+}$ CO3 does take H and forms CO2 + H2O alongside:
2M(H2O)6$^{3+}$ + 3CO$^{2-}$ --> 2M(H20)3(OH)3 + 3CO2 + 3H2O fizzing will be seen
M(H2O)6$^{2+}$ + CO$^{2-}$3 --> MCO3 + 6H2O
But With M$^{3+}$ CO3 does take H and forms CO2 + H2O alongside:
2M(H2O)6$^{3+}$ + 3CO$^{2-}$ --> 2M(H20)3(OH)3 + 3CO2 + 3H2O fizzing will be seen
10
Sodium carbonate colours?
Fe2+ = green pt
Cu2+ = green-BLUE pt
Al3+ = white pt +effervescene
Fe3+ = brown pt + effervescene
Cu2+ = green-BLUE pt
Al3+ = white pt +effervescene
Fe3+ = brown pt + effervescene
11
Wr