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Chemistry > 15.2 > Flashcards

15.2 Flashcards

1
Q

what are the 4 main reactions transition metals undergo

A

redox
acid-base reaction
ligand exchange
coordination number change

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2
Q

what is an acid-base reaction

A

one or more ligand gains or loses a hydrogen ion

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3
Q

what is a ligand exchange

A

one or more ligand around the transition metal is replaced by a different ligand

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4
Q

what is a coordination number change

A

number of ligands change

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5
Q

what happens in the oxidation of Fe (iron)

A

oxidation number goes from 2+ to 3+
goes from a pale green to yellow/brown

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6
Q

what is observed when aqueous sodium hydroxide is added to copper(II) sulfate solution

A

pale blue solution forms a blue precipitate

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7
Q

what is the equation for the reaction between aqueous sodium hydroxide and copper(II) sulfate solution

A

[Cu(H2O)6]2+ + 2OH- -> [Cu(H2O)4(OH)2] + 2H2O

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8
Q

what type of reaction is the reaction between aqueous sodium hydroxide and copper(II) sulfate solution and why

A

acid-base reaction because the 2 hydroxide ions have removed hydrogen ions from the water ligands

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9
Q

what is amphoteric behavior

A

the ability of a species to react with both acids and bases

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10
Q

what happens when acid is added to tetraaquadihydroxocopper [Cu(H20)4(OH)2]

A

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

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11
Q

what reaction occurs when a small amount of ammonia solution is added to hexaaquacopper(II)

A

ammonia acts as a base
[Cu(H2O)6]2+ + 2NH3 -> [Cu(H2O)4(OH)2] + 2NH4+
blue solution -> blue precipitate

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12
Q

what reaction occurs when excess ammonia solution is added to hexaaquacopper(II) (copper sulfate solution)

A

ligand exchange reaction
precipitate dissolves forms dark blue solution
[Cu(H2O)6]2+ + 4NH3 -> [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-

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13
Q

what reaction occurs when concentrated hydrochloric acid is added to hexaaquacopper(II) (copper sulfate solution)

A

ligand exchange
coordination number change
[Cu(H2O)6]2+ + 4Cl- <=> [CuCl4]2- + 6H2O
blue -> green -> yellow

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14
Q

what is the name of the ion [CuCl4]2-

A

tetrachlorocuprate(II)

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15
Q

what reaction occurs between hexaaquacobalt(II) and alkalis

A

[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

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16
Q

what reaction occurs when a small amount of ammonia is added to hexaaquacobalt(II)

A

[Co(H20)6]+2 + 2NH3 -> [Co(H2O)4(OH)2] + 2NH4+
acid-base reaction
pink solution -> blue precipitate

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17
Q

what reaction occurs when excess ammonia is added to hexaaquacobalt(II)

A

[Co(H2O)6]2+ + 6NH3 -> [Co(NH3)6]2+ + 4H2O + 2OH-
ligand exchange
pink solution -> blue precipitate -> brown solution

18
Q

what happens to the brown solution [Co(NH3)6]2+ when left standing in air

A

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

19
Q

what reaction occurs between hydrochloric acid and hexaaquacobalt(II)

A

[Co(H2O)6]2+ + 4Cl- -> [CoCl4]2- + 6H2O
ligand exchange
change in coordination number
pink solution -> blue solution

20
Q

what reaction occurs between hexaaquairon(II) and aqueous sodium hydroxide

A

[Fe(H2O)6]2+ + 2OH- -> [Fe(H2O)4(OH)2] + 2H2O
acid base reaction
pale green solution -> green precipitate

21
Q

what reaction occurs between hexaaquairon(II) and ammonia

A

[Fe(H2O)6]2+ + 2NH3 -> [Fe(H2O)4(OH)2] + 2NH4+
acid base reaction
pale green solution -> green precipitate

22
Q

what happens when the green precipitate [Fe(H2O)4(OH)2] is left standing in air

A

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]

23
Q

what reaction occurs between hexaaquairon(III) and aqueous sodium hydroxide

A

[Fe(H2O)6]3+ + 3OH- -> [Fe(H2O)3(OH)3 + 3H2O
acid base reaction
yellow brown solution -> brown precipitate

24
Q

what reaction occurs when ammonia is added to hexaaquairon(III)

A

[Fe(H2O)6]3+ + 3NH3 -> [Fe(H2O)3(OH)3] + 3H2O
acid base reaction
yellow/brown solution -> brown precipitate

25
Q

what reaction occurs when excess ammonia is added to hexaaquairon(III)

A

no further reaction occurs

26
Q

what makes the colours of chromium complexes so hard to define

A

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

27
Q

what reaction occurs when aqueous sodium hydroxide is added to hexaaquachromium(III)

A

[Cr(H2O)6]3+ + 3OH- -> [Cr(H2O)3(OH)3 + 3H2O
acid base reaction
green/violet solution -> green precipitate

28
Q

what reaction occurs when ammonia is added to hexaaquachromium(III)

A

[Cr(H2O)6]3+ + 3NH3 -> [Cr(H2O)3(OH)3] + 3NH4+
acid base reaction
green/violet solution -> green precipitate

29
Q

what reaction occurs when excess sodium hydroxide solution is added to triaquatrihydroxychromium

A

[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

30
Q

what reaction occurs when excess ammonia is added to triaquatrihydroxychromium

A

[Cr(H2O)3(OH)3] + 6NH3 -> [Cr(NH3)6]3+ + 3H2O + 3OH-
ligand exchange
green precipitate -> slowly dissolves & forms purple solution

31
Q

how can you oxidise chromium(III) to chromium(VI)

A

add hydrogen peroxide
green solution -> yellow solution

32
Q

what reaction occurs when hydrogen peroxide is added to hexahydroxychromium(III)

A

2[Cr(OH)6]3- + 3H2O2 -> 2CrO42- + 2OH- + 8H2O
oxidation
green solution -> yellow solution

33
Q

what reaction occurs when chromate(VI) ions are placed in acidic conditions

A

2CrO42- + 2H+ <=> Cr2O72- + H2O
yellow solution -> orange solution

34
Q

what is the colour change and equation for the reduction of dichromate(VI) from +3 to +2 with zinc in acidic conditions

A

Cr2O72- + 14H+ + 3Zn -> 2Cr3+ + 7H2O + 3Zn2+
orange -> green

35
Q

what is the colour change and equation for the reduction of chromium(III) to chromium(II) with zinc in acidic conditions

A

2Cr3+ + Zn -> 2Cr2+ + Zn2+
green -> blue

36
Q

what is the colour of [Cr(H2O)6]^3+

A

green solution

37
Q

what is the colour of [Cr(H2O)6]^3-

A

green solution

38
Q

what is the colour of CrO4^2-

A

yellow solution

39
Q

what is the colour of [Cr(H2O)3(OH)3]

A

green precipitate

40
Q

what is the colour of [Cr(OH)6]3-

A

green solution

41
Q

what is the colour of [Cr(NH3)6]^3+

A

violet solution

42
Q

what is the colour of [Cr(H2O)6]^2+

A

blue solution

Chemistry (46 decks)

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