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Chemistry > Transition Elements > Flashcards

Transition Elements Flashcards

D-block element, The formation and shapes of complex ions, Stereoisomerism in complex ions, Ligand substitution and precipitation, Redox and qualitative analysis.

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1
Q

What are the two irregularities in the d-block in terms of electron configuration?

A

Chromium: 3d5 4s1 instead of 3d4 4s2 Copper: 3d10 4s1 instead of 3d9 4s2

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2
Q

Why do these irregularities exist in the d block electron configurations?

A

A half filled and a fully filled d sub shell gives greater stability to these atoms.

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3
Q

What are transition elements?

A

D-block elements that form at least one ion with a partially filled d-orbital.

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4
Q

Which d-block elements are excluded from being transition elements?

A

Scandium and zinc

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5
Q

What are the properties of the transition elements?

A

Form compounds in which the transition element has different oxidation states Form coloured compounds Elements and compounds can act as catalysts

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6
Q

What colours are the various ions of Chromium?

A

+3 green +6 orange

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7
Q

What colours are the various ions of Copper?

A

+2 blue

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8
Q

What colour is potassium dichromate(VI)?

A

Orange

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9
Q

What colour is cobalt(II) chloride and what colour is the solution formed when hydrochloric acid is added? And when water is added after?

A

Pink

Purple

Pink again

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10
Q

What colour is nickel(II) sulfate?

A

Green

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11
Q

What colour is hydrated copper(II) sulfate?

A

Blue

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12
Q

Define what a complex ion is

A

A transition metal ion bonded to ligands by coordinate bonds.

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13
Q

Define coordination number

A

The number of coordinate bonds attached to the central metal ion.

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14
Q

Define what a ligand is

A

A molecule or ion that can donate a pair of electrons to the transition metal ion to form a coordinate bond.

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15
Q

What is meant by a monodentate ligand?

A

A ligand that is able to donate one pair of electrons to a central metal ion.

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16
Q

Give 5 examples of common monodentate ligands and their charges

A

Water H2O neutral

Ammonia NH3 neutral

Chloride Cl-

Hydroxide OH-

Cyanide CN-

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17
Q

Define denticity

A

The number of separate sites in a molecule or ion that can donate an electron pair to a transition metal ion.

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18
Q

What shape is created from a complex ion having a coordination number of 6?

A

Octahedral

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19
Q

What shapes can be created from a complex ion having a coordination number of 4?

A

Tetrahedral OR Square planar

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20
Q

When is a square planar shape formed in a complex ion?

A

When the transition metal in the complex ion has eight d-electrons in the highest energy d-sub-shell.

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21
Q

What is stereoisomerism?

A

Same structural formula but a different arrangement of the atoms in space.

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22
Q

What are the two types of stereoisomerism?

A

Cis-trans isomerism Optical isomerism

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23
Q

When can complex ions show both types of stereoisomerism?

A

Six coordinate complex ions containing monodentate and bidentate ligands.

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24
Q

What is optical isomerism?

A

Non-superimposable mirror images of each other. Called enantiomers

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25
Q

Define ligand substitution

A

One ligand in a complex ion is replaced by another ligand.

26
Q

Describe ligand substitution of aqueous copper(II) ions with ammonia

A
  1. Excess of aq. ammonia added to solution containing [Cu(H20)6]2+.
  2. 4 ammonia ligands replace replace 4 of the waters to form [Cu(NH3)4(H2O)2]2+
  3. Pale blue solution → Dark blue solution
  4. *when adding ammonia dropwise, blue precipitate of Cu(OH)2 (s) first forms as ammonia reacts w/ water to form hydroxide ions which bond with copper ions*
27
Q

Describe ligand substitution of aqueous copper(II) ions with chloride ions

A
  1. Concentrated hydrochloric acid added to solution containing [Cu(H20)6]2+
  2. 4 chloride ligands replace replace 6 of the waters to form [CuCl4]2- which is tetrahedral. Chloride ligands are larger than water ligands, which means fewer can fit around the central metal ion.
  3. Pale blue solution → yellow solution
  4. *After first few drops of HCl, green solution may be observed: result of mixing of blue and yellow solutions. If water is added to yellow solution, it will turn blue again.*
28
Q

Why does the shape of the aqueous copper (II) ion change from octahedral to tetrahedral when it reacts with chloride ions?

A

Chloride ligands are larger in size than water ligands so fewer of them can fit around the Cu2+ ion.

29
Q

What is formed when chromium(III) potassium sulphate (KCr(SO4)2•12H20 or chrome alum) is dissolved in water?

A

The complex ion [Cr(H2O)6]3+ is formed. A pale purple solution.

30
Q

What is formed instead when only chromium(III) sulphate is dissolved in water?

A

The complex ion [Cr(H2O)5SO4]+ is formed (sulphate ion replaces one of the water ligands). A green solution.

31
Q

Describe the reaction between aqueous chromium (III) ions and an excess of aqueous ammonia (when added dropwise).

A
  1. Grey-green ppt. of Cr(OH)3 formed (as ammonia reacts w/ water to form hydroxide ions).
  2. Ppt. then dissolves in excess ammonia and overall the 6 water ligands are replaced by 6 ammonia ligands to form [Cr(NH3)6]3+.
  3. Overall:

violet solution → grey-green ppt. → purple solution

32
Q

How does ligand substitution help with gas exchange in blood?

A

In haemoglobins there is a central Fe2+ ion that can bind to oxygen gas. The oxygen is released to cells and carbon dioxide can bond to the Fe2+ where it is released in the lungs.

33
Q

What is a precipitation reaction?

A

Two aqueous solutions containg ions react together to form an insoluble ionic solid.

Transition metal ions react with hydroxide and ammonia ions to for precipitates. Some precipitates redissolve in excess NaOH or NH3 solution to form new complex ions in solution.

34
Q

Describe the precipitation reaction of Cu2+(aq) with NaOH

A

Blue solution reacts to form a blue precipitate of copper(II) hydroxide. Insoluble in excess NaOH.

35
Q

How do Fe2+, Fe3+ and Mn2+ react with an excess of aqueous ammonia?

A

Same way as they react with NaOH to form same hydroxide preciptitates. Insoluble in excess ammonia.

36
Q

What metals form square planar complex ions?

A

Ni, Pd & Pt

37
Q

Why is carbon monoxide dangerous?

A

CO binds more strongly to the haemoglobin than O2 so even a small concentration in the lungs can prevent a large proportion of haemoglobin molecules from carry oxygen. The bond is so strong that the process is irreversible.

38
Q

What does oxyhaemoglobin look like?

A
39
Q

What is the catalyst used in the Haber process?

A

Iron

40
Q

What is the catalyst used in the Contact process?

A

Vanadium (V) oxide

V2O5

41
Q

What is the catalyst used in hydrogenation (of vegetable fats in the manufacture of margarine)?

A

Nickel

Ni

42
Q

What catalyst is used in the reaction between iodide and peroxodisulfate ions and what type of catalyst is it?

What are the steps of this reaction?

A

Fe2+(aq)

Homogenous

  1. S2O82- (aq) + Fe2+(aq) → 2SO42-(aq) + Fe3+(aq)
  2. Fe3+(aq) + 2I-(aq) → I2 (aq) + Fe2+(aq)
43
Q

What is the catalyst used in the reaction between zinc metal and acids?

A

Cu2+ (aq)

44
Q

What property do complex ions have to have to not show optical isomerism?

A

The mirror images have to be superimposable.

45
Q

What does ethan-1,2-diamine (en) look like?

A
46
Q

What does oxalate (ethandiolate) “ox” look like?

A
47
Q

What does cis-platin look like?

A
48
Q

What conditions have to be met for cis-trans isomerism?

A
  • Complexes w/ corordination umber 4 and square planar shape
  • Complexes w/ corordination number 6 that contain 4 of 1 ligand and two of another
  • Complexes w/ coordination number 6 that contain 2 bidentate ligands and two monodentate ligands.
49
Q

When can complex ions show optical isomerism?

A
  • Coord. number 6 , 2 bidentate & 2 monodentate ligands. Applies only to cis-isomer.
  • Coord. number 6 w/ 3 bidentate ligands
  • Coord. number 6 with hexadentate ligands
50
Q

What is the significance of cis-platin?

A

it is the cis- isomer of [PtCl2(NH3)2]. It is used as an anti-cancer drug. It undergoes hydrolysis at the tumor site and forms a platinum complex (essentially free platinum ions) inside a cell which binds to the DNA to prevent replication (transcription).

51
Q

Describe the reaction between Mn2+ ions and aqueous sodium hydroxide.

A

Pale pink solution reacts to form an light brown ppt. of manganese (II) hydroxide which darkens standing in air.

Mn2+ + 2OH-(aq) → Mn(OH)2 (s)

Ppt. is insoluble in excess NaOH solution.

52
Q

Describe the reaction between Fe3+ ions and aqueous sodium hydroxide.

A

Pale yellow solution reacts to form an orange-brown ppt. of iron (III) hydroxide.

Fe3+ + 3OH-(aq) → Fe(OH)3 (s)

Ppt. is insoluble in excess NaOH solution.

53
Q

Describe the reaction between Fe2+ ions and aqueous sodium hydroxide.

A

Pale green solution reacts to form a green ppt. of iron (II) hydroxide.

Fe2+ + 2OH-(aq) → Fe(OH)2 (s)

Ppt. is insoluble in excess NaOH solution but turns brown at surface in air as iron (II) is oxidised to iron (III): Fe(OH)2 (s) → Fe(OH)3 (s)

54
Q

Describe the reaction between Cu2+ ions and aqueous sodium hydroxide.

A

Blue solution reacts to form a blue ppt. of copper (II) hydroxide.

Cu2+ + 2OH-(aq) → Cu(OH)2 (s)

Ppt. is insoluble in excess NaOH solution.

55
Q

Describe the reaction between Cr3+ ions and sodium hydroxide solution

A
  1. Violet solution → Grey-green ppt. of Cr(OH)3

Cr3+(aq) + 3OH-(aq) → Cr(OH)3 (s)

  1. Precipitate dissolves in excess NaOH to form complex where:

Overall: 6 water ligands have been replaced by 6 hydroxide ligands

Going from ppt. to solution: 3 hydroxides are added:

Cr(OH)3 (s) + 3OH-(aq) → [Cr(OH)6]3-(aq)

56
Q

Decribe the reaction between Cu2+ ions and excess iodide ions.

A
  • I- is oxidised to brown iodine
  • Cu2+ is reduced to Cu+
  • The Cu+ forms a white ppt. of copper (I) oxide with the iodide ions which haven’t been oxidised.
  • 2Cu2+(aq) + 4I-(aq) → 2CuI (aq) + I2 (s)
  • Test tube has a brown solution with white ppt. formed at the bottom.
57
Q

Describe the reaction of copper (I) oxide, Cu20, with hot dilute sulfuric acid.

A
  • Brown ppt. of copper formed.
  • Blue solution of copper (II) sulphate also formed.
  • Copper 1+ ions simultaneously reduced to Cu(s) and oxidised to Cu2+ as part of copper (II) sulphate ⇒ disproportionation reaction.
58
Q

Describe the reaction between iron (II) ions and manganate (VII) ions in acid conditions.

A
  • Fe2+ oxidised to Fe3+
  • MnO4- reduced to Mn2+
  • Purple solution → colourless
59
Q

Describe the reaction between Fe3+ ions and iodide ions

A
  • Fe3+ ions reduced to Fe2+
  • I- ions oxidised to I2
  • orange-brown solution → brown iodine solution (pale green solution of Fe2+ is formed but colour is obscured by iodine solution)
60
Q

Describe the reduction of dichromate (VI) ions (by zinc)

A
  • Cr2O72-(aq) reduced to Cr3+(aq) ions
  • orange solution → green solution
  • In an excess of zinc, Cr3+ ions are further reduced to Cr2+, which forms a pale blue solution.
61
Q

Describe the oxidation of Cr3+ by hydrogen peroxide, H2O2

A
  • Hot alkaline H2O2 oxidises chromium (III) in Cr3+ to chromium (VI) in CrO42-
  • Oxygen is simultaneously reduced from -1 in H2O2 to -2 in CrO42-
  • Green solution → orange solution

Chemistry (11 decks)

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