15.2 Flashcards
what are the 4 main reactions transition metals undergo
redox
acid-base reaction
ligand exchange
coordination number change
what is an acid-base reaction
one or more ligand gains or loses a hydrogen ion
what is a ligand exchange
one or more ligand around the transition metal is replaced by a different ligand
what is a coordination number change
number of ligands change
what happens in the oxidation of Fe (iron)
oxidation number goes from 2+ to 3+
goes from a pale green to yellow/brown
what is observed when aqueous sodium hydroxide is added to copper(II) sulfate solution
pale blue solution forms a blue precipitate
what is the equation for the reaction between aqueous sodium hydroxide and copper(II) sulfate solution
[Cu(H2O)6]2+ + 2OH- -> [Cu(H2O)4(OH)2] + 2H2O
what type of reaction is the reaction between aqueous sodium hydroxide and copper(II) sulfate solution and why
acid-base reaction because the 2 hydroxide ions have removed hydrogen ions from the water ligands
what is amphoteric behavior
the ability of a species to react with both acids and bases
what happens when acid is added to tetraaquadihydroxocopper [Cu(H20)4(OH)2]
the blue precipitate disappears as the hydrogen ions react with the hydroxide ligands and convert them back to water ligands to form hexaaquacopper(II) which is a blue solution
what reaction occurs when a small amount of ammonia solution is added to hexaaquacopper(II)
ammonia acts as a base
[Cu(H2O)6]2+ + 2NH3 -> [Cu(H2O)4(OH)2] + 2NH4+
blue solution -> blue precipitate
what reaction occurs when excess ammonia solution is added to hexaaquacopper(II) (copper sulfate solution)
ligand exchange reaction
precipitate dissolves forms dark blue solution
[Cu(H2O)6]2+ + 4NH3 -> [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-
what reaction occurs when concentrated hydrochloric acid is added to hexaaquacopper(II) (copper sulfate solution)
ligand exchange
coordination number change
[Cu(H2O)6]2+ + 4Cl- <=> [CuCl4]2- + 6H2O
blue -> green -> yellow
what is the name of the ion [CuCl4]2-
tetrachlorocuprate(II)
what reaction occurs between hexaaquacobalt(II) and alkalis
[Co(H2O)6]2+ + 2OH- -> [Co(H2O)4(OH)2] + 2H2O
pink solution -> blue precipitate
acid-base reaction
when left standing the solution goes back to pink
what reaction occurs when a small amount of ammonia is added to hexaaquacobalt(II)
[Co(H20)6]+2 + 2NH3 -> [Co(H2O)4(OH)2] + 2NH4+
acid-base reaction
pink solution -> blue precipitate
what reaction occurs when excess ammonia is added to hexaaquacobalt(II)
[Co(H2O)6]2+ + 6NH3 -> [Co(NH3)6]2+ + 4H2O + 2OH-
ligand exchange
pink solution -> blue precipitate -> brown solution
what happens to the brown solution [Co(NH3)6]2+ when left standing in air
it is oxidised from cobalt +2 to +3 and the solution goes yellow but is still a very dark solution due formation of other products
what reaction occurs between hydrochloric acid and hexaaquacobalt(II)
[Co(H2O)6]2+ + 4Cl- -> [CoCl4]2- + 6H2O
ligand exchange
change in coordination number
pink solution -> blue solution
what reaction occurs between hexaaquairon(II) and aqueous sodium hydroxide
[Fe(H2O)6]2+ + 2OH- -> [Fe(H2O)4(OH)2] + 2H2O
acid base reaction
pale green solution -> green precipitate
what reaction occurs between hexaaquairon(II) and ammonia
[Fe(H2O)6]2+ + 2NH3 -> [Fe(H2O)4(OH)2] + 2NH4+
acid base reaction
pale green solution -> green precipitate
what happens when the green precipitate [Fe(H2O)4(OH)2] is left standing in air
the colour changes from a green precipitate to a brown precipitate because it has been oxidised by air to form [Fe(H2O)3(OH)3]
what reaction occurs between hexaaquairon(III) and aqueous sodium hydroxide
[Fe(H2O)6]3+ + 3OH- -> [Fe(H2O)3(OH)3 + 3H2O
acid base reaction
yellow brown solution -> brown precipitate
what reaction occurs when ammonia is added to hexaaquairon(III)
[Fe(H2O)6]3+ + 3NH3 -> [Fe(H2O)3(OH)3] + 3H2O
acid base reaction
yellow/brown solution -> brown precipitate
what reaction occurs when excess ammonia is added to hexaaquairon(III)
no further reaction occurs
what makes the colours of chromium complexes so hard to define
some compounds have different colours as solids and aqueous solutions
the colour of the solution depends on concentration
the presence of dissolved oxygen in an aqueous solution can affect the colour observed
what reaction occurs when aqueous sodium hydroxide is added to hexaaquachromium(III)
[Cr(H2O)6]3+ + 3OH- -> [Cr(H2O)3(OH)3 + 3H2O
acid base reaction
green/violet solution -> green precipitate
what reaction occurs when ammonia is added to hexaaquachromium(III)
[Cr(H2O)6]3+ + 3NH3 -> [Cr(H2O)3(OH)3] + 3NH4+
acid base reaction
green/violet solution -> green precipitate
what reaction occurs when excess sodium hydroxide solution is added to triaquatrihydroxychromium
[Cr(H2O)3(OH)3] + OH- -> [Cr(H2O)2(OH)4]- + 2H2O
or if concentrated
[Cr(H2O)3(OH)3] + 3OH- -> [Cr(OH)6]3- + 3H20
acid base reaction
green precipitate -> green solution
what reaction occurs when excess ammonia is added to triaquatrihydroxychromium
[Cr(H2O)3(OH)3] + 6NH3 -> [Cr(NH3)6]3+ + 3H2O + 3OH-
ligand exchange
green precipitate -> slowly dissolves & forms purple solution
how can you oxidise chromium(III) to chromium(VI)
add hydrogen peroxide
green solution -> yellow solution
what reaction occurs when hydrogen peroxide is added to hexahydroxychromium(III)
2[Cr(OH)6]3- + 3H2O2 -> 2CrO42- + 2OH- + 8H2O
oxidation
green solution -> yellow solution
what reaction occurs when chromate(VI) ions are placed in acidic conditions
2CrO42- + 2H+ <=> Cr2O72- + H2O
yellow solution -> orange solution
what is the colour change and equation for the reduction of dichromate(VI) from +3 to +2 with zinc in acidic conditions
Cr2O72- + 14H+ + 3Zn -> 2Cr3+ + 7H2O + 3Zn2+
orange -> green
what is the colour change and equation for the reduction of chromium(III) to chromium(II) with zinc in acidic conditions
2Cr3+ + Zn -> 2Cr2+ + Zn2+
green -> blue
what is the colour of [Cr(H2O)6]^3+
green solution
what is the colour of [Cr(H2O)6]^3-
green solution
what is the colour of CrO4^2-
yellow solution
what is the colour of [Cr(H2O)3(OH)3]
green precipitate
what is the colour of [Cr(OH)6]3-
green solution
what is the colour of [Cr(NH3)6]^3+
violet solution
what is the colour of [Cr(H2O)6]^2+
blue solution
