Reactions of ions in aqueous solution Flashcards
are metal aqua ions acidic or alkaline in solution?
acidic
what affects how acidic the solution of metal aqua ions formed is?
the charge on the ion: higher charge = more acidic in solution
what is H3O+?
a hydronium ion
what happens to 2+ complexes in water?
they dissociate weakly so are not very acidic
what happens to 3+ complexes in water?
they dissociate more readily than 2+ complexes so are more acidic
why are 3+ complexes more acidic than 2+ complexes when in solution?
3+ complex ions have a higher charge density so are more polarising than 2+ ions - they attract electrons in the O-H bond in the water ligands more strongly, which weakens the bond - so it is more likely that the H+ ion will be released
how can you further hydrolyse metal-aqua ions?
using OH- ions
the OH- ions remove H+ and cause the eqm. that was previously established with hydrolysis to shift right
at happens when you add water to metal-aqua ions
they are hydrolysed and an eqm. is established
what does the further hydrolysis of metal-aqua ions eventually lead to?
the formation of a neutral complex that is solid and so forms a ppt. in solution
how many steps are there in the continuous hydrolysis of metal-aqua 3+ ions?
3
e.g. M(H2O)3(OH)3 (s)
how many steps are there in the continuous hydrolysis of metal-aqua 2+ ions? why?
2
because only 2 water ligands need to be deprotonated to form a neutral complex
e.g. M(H2O)4(OH)2 (s)
what is special about aluminium hydroxide [Al(H2O)3(OH)3]?
it is amphoteric
what happens when ammonia is added to metal-aqua ions?
they form metal hydroxides
what can sometimes happen when excess ammonia is added to metal-aqua ions?
ligand-substitiution reactions
how does ammonia exist in solution?
NH3 + H2O ⇌ NH4+ + OH-
what happens when excess ammonia is added to [Cu(OH)2(H2O)4]?
partial ligand substitution:
[Cu(OH)2(H2O)4] + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ + 2OH- + 2H2O
what does adding sodium carbonate to 2+ metal-aqua ions form?
metal carbonates precipitates
e.g. [M(H2O)6]2+ + CO32- ⇌ MCO3 + 6H2O
(complete substitution of all the water ligands)
what does adding sodium carbonate to 3+ metal-aqua ions form? why?
[M(OH)3(H2O)3] ppt. because the ions are more acidic so the carbonate ions react with the H+ ions instead of displacing the water ligands
note that carbon dioxide is also produced so fizzing is seen
how can you identity metal ion solutions?
by reacting them with NH3, NaOH and Na2CO3 and observing what happens
which 4 metal-aqua ions need to be learnt?
(and the test-tube reactions known)
[Fe(H2O)6]2+
[Cu(H2O)6]2+
[Al(H2O)6]3+
[Fe(H2O)6]3+
which metal-aqua ion dissolves in excess NaOH?
[Al(H2O)6]3+
how do you carry out the test tube reactions?
add a small amount of reagent and observe, then add it in excess and observe (only one of them should redissolve but they will all initially form a ppt.)
which metal-aqua ion dissolves in excess NH3?
[Cu(H2O)6]2+
which metal-aqua ions will produce fizzing (CO2) when they react with Na2CO3?
[Al(H2O)6]3+
[Fe(H2O)6]3+
what happens when Fe2+ reacts with air?
it oxides to form Fe3+
what formula do metal ions dissolved in water have?
[M(H2O)6]n+ (metal-aqua ions)
can be simplified to Mn+
where M = metal
colour of [Cu(H2O)6]2+
a.k.a Cu2+ (aq.)
blue (aq.)
colour of [Cu(OH)2(H2O)4]
pale blue precipitate
colour of [Cu(NH3)4(H2O)2]2+
dark blue (aq.)
colour of CuCo3
green-blue precipitate
colour of [Fe(H2O)6]2+
a.k.a Fe2+ (aq.)
pale green (aq.)
colour of [Fe(OH)2(H2O)4]2+
green precipitate
colour of FeCO3
green precipitate
colour of [Fe(H2O)6]3+
a.k.a Fe3+ (aq.)
yellow (aq.)
colour of [Fe(OH)3(H2O)3]
brown precipitate
colour of [Fe(OH)3(H2O)3] (from addition of Na2CO3)
brown precipitate
colour of [Al(H2O)6]3+
a.k.a Al3+ (aq.)
colourless
colour of [Al(OH)3(H2O)3]
white precipitate
