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Year 13 - Chemistry > C24 - Transition Elements > Flashcards

C24 - Transition Elements Flashcards

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1
Q

What are transition elements?

A

They’re d-block elements that form at least 1 ion with a partially filled d-orbital.

Zn and Sc aren’t as Zn has a full d orbital and Sc have an empty d orbital.

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2
Q

Which elements differ from the usual electron configurations for transition elements?

A

Cr and Cu which have 1 electron on their 4s orbital instead of 2

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3
Q

From which orbitals do transition elements first lose electrons when forming ions?

A

The 4s orbital (then the 3d).

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4
Q

What are the properties of transition elements and their compounds?

A

They form coloured compounds.

The elements and their compounds can act as catalysts.

They form compounds in which the transition element has different oxidation states.

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5
Q

What’s a complex ion?

A

When one or more molecules or negatively charged ions bond to a central metal ion.

These molecules are known as ligands.

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6
Q

What’s a ligand?

A

Any molecule or ion that can donate a pair of electrons to a central metal ion to form coordinate bonds.

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7
Q

What is the coordination number?

A

The coordination number of a complex ion indicates the number of coordinate bonds attached to the central metal ion.

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8
Q

How are complex ions represented?

A

They’re written and drawn in square brackets.

The ligand is inside round brackets.

The overall charge of the complex is shown outside the square brackets. This is the sum of charges on the central metal ion and any ligands present.

E.g. [Cr(H2O)6] ^3+

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9
Q

What is an example of a complex ion formed when hydrated chromium chloride, CrCl3-6H2O, is dissolved in water?

A

[Cr(H2O)6] ^3+

Cr 3+ is the central metal ion and water acts as a ligand, with each water molecule donating a lone pair of electrons from the oxygen atom to the metal ion.

Here, 6 coordinate bonds form.

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10
Q

What are monodentate ligands?

A

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

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11
Q

What are the common monodentate ligands?

A

Water (neutral)

Ammonia (neutral)

Chloride (-1)

Cyanide (-1)

Hydroxide (-1)

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12
Q

What’s a bidentate ligand?

A

A ligand able to donate two lone pairs of electrons to the central metal ion to form two coordinate bonds.

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13
Q

What are the (2) common bidentate ligands?

A

1,2-diaminoethane NH2CH2CH2NH2
(en)

Ethandioate ion C2O4 ^2-

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14
Q

What shapes can complex ions form?

What’s the bond angle and coordination number of each?

A

Octahedral (90°)
Coordination number = 6

Square planar (90°)
Coordination number = 4

Tetrahedral (109.5°)
Coordination number = 4

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15
Q

What shapes can complex ions form?

A

Octahedral (90°)
Coordination number = 6

Square planar (90°)
Coordination number = 4

Tetrahedral (109.5°)
Coordination number = 4

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16
Q

What two types of stereoisomer can complex ions display?

A

Cis-Trans isomerism

Optical isomerism

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17
Q

How does cis-trans isomerism occur in complex ions?

A

There’s no double bond involved.
The shape of the complex holds groups in different orientations about the central metal ion.

It can occur in some square planar and octahedral complex ions.

  • In the cis isomer, the 2 identical groups are adjacent to each other.
  • In the trans isomer, the two identical groups are opposite each other.
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18
Q

Give an example of a square planar complex ion which can form cis-trans isomerism:

A

The complex:
[Pd(NH3)2Cl2]

In the cis isomer, the 2 identical groups are adjacent to each other.

In the trans isomer, the two identical groups are opposite each other.

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19
Q

How does cis-trans isomerism form in octahedral complexes?

Give an example:

A

It can occur in complexes containing four of one type of ligand and two of another type.

(Monodentate)
E.g. [Co(NH3)4Cl]+

It can also form with bidentate ligands:
[Co(en)2Cl2]+

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20
Q

How does optical isomerism form in octahedral complexes?

A

It can only occur in complexes containing two or more bidentate ligands.

The cis isomer is able to form optical isomerism only, NOT the trans isomer.

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21
Q

What’s a ligand substitution reaction?

A

A reaction where one ligand in a complex ion is replaced by another.

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22
Q

What’s cis-platin used for?

A

[Pt(NH3)Cl2]
Used as an anti cancer drug.

It binds to DNA and prevent cell division, causing cell death.

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23
Q

What’s the significance of cis-platin?

A

[Pt(NH3)Cl2]
It’s used as an anti cancer drug.

It binds to DNA and prevent cell division, causing cell death.

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24
Q

How does ligand substitution allow haemoglobin to transport oxygen in the blood?

A

Haemoglobin has Fe 2+ central metal ions which bind to oxygen gas in the lungs.

The oxygen can then be transported and released where needed. (It can be substituted for CO2 which is returned to the lungs and exhaled).

However the Fe 2+ will form a stronger bond with CO.

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25
Q

How does ligand substitution occur in haemoglobin?

A

It has an Fe 2+ central metal ion which binds to oxygen.

The oxygen can then be released and substituted (e.g. for CO2 or CO).

CO forms a stronger bond to the metal ion which is irreversible.

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26
Q

How do precipitation reactions take place with transition metal ions?

A

Transition metals in aqueous solution react with aqueous NaOH or NH3 to form precipitates (when not in excess).

If the NaOH or NH3 are in excess, complex ions would form.

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27
Q

What happens when Cu 2+ ions ([Cu(H2O)6] ^2+) react with a small amount of ammonia (NH3) or sodium hydroxide (OH-)?

A

A precipitation reaction occurs.

Pale blue precipitate “Cu(OH)2” is formed

Cu 2+ + OH-/(NH3) —> Cu(OH)2

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28
Q

What is formed when copper (II) sulphate is dissolved in water?

A

It forms the pale blue complex ion, [Cu(H2O)6] ^2+ in aqueous solution.

29
Q

What happens when a small amount of NH3 or NaOH (OH-) is added to the pale blue copper complex ion: [Cu(H2O)6] ^2+ ?

A

A precipitation reaction takes place.

Pale blue precipitate, Cu(OH)2 is formed.

Cu 2+ + OH-/NH3 —> Cu(OH)2

30
Q

What happens when an excess of NH3 is added to the pale blue copper complex ion: [Cu(H2O)6] ^2+ ?

A

A ligand substitution reaction occurs.

A dark blue solution containing [Cu(NH3)4(H2O)2] 2+ is formed (plus 4 H2O molecules).

[Cu(H2O)6] ^2+ + 4NH3 —> 4H2O + [Cu(NH3)4(H2O)2] 2+

31
Q

What’s the equation for the ligand substitution reaction when excess ammonia is added to Cu 2+ ions ([Cu(H2O)6] ^2+) ?

A

[Cu(H2O)6] ^2+ + 4NH3 —> 4H2O + [Cu(NH3)4(H2O)2] 2+

4 miles of water are substituted for ammonia and a dark blue solution forms.

32
Q

What colour are Cu 2+ ions in [Cu(H2O)6] ^2+ ?

A

Pale blue

33
Q

What colour are Cr 3+ ions in [Cr(H2O)6] ^3+?

A

Violet

34
Q

What colour are Fe 2+ ions in [Fe(H2O)6] ^2+ ?

A

Pale green

35
Q

What colour are Fe 3+ ions in [Fe(H2O)6] ^3+ ?

A

Yellow/orange

36
Q

What colour are Mn 2+ ions in [Mn(H2O)6] ^2+ ?

A

Pale pink

37
Q

What colour precipitate is formed when [Cu(H2O)6] ^2+ reacts with a small amount of NH3 / OH-?

A

Pale blue precipitate

Cu(OH)2

38
Q

What colour precipitate is formed when [Cr(H2O)6] ^3+ reacts with a small amount of NH3 / OH-?

A

Grey/green precipitate

Cr(OH)3

39
Q

What colour precipitate is formed when [Fe(H2O)6] ^3+ reacts with a small amount of NH3 / OH-?

A

Orange/brown precipitate

Fe(OH)3

40
Q

What colour precipitate is formed when [Fe(H2O)6] ^2+ reacts with a small amount of NH3 / OH-?

A

Green precipitate

Fe(OH)2

41
Q

What colour precipitate is formed when [Mn(H2O)6] ^2+ reacts with a small amount of NH3 / OH-?

A

Light brown precipitate

Mn(OH)2

42
Q

What colour solution is formed when [Cu(H2O)6] ^2+ reacts with an excess of NH3?

(Ligand substitution reaction)

A

Dark blue solution
[Cu(NH3)4(H2O)2] 2+

The Cu(OH)2 precipitate formed (with small amounts of NH3) dissolves in excess.

43
Q

What colour solution is formed when [Cu(H2O)6] ^2+ reacts with an excess of NaOH (OH-)?

(Ligand substitution reaction)

A

No change - pale blue

The pale blue Cu(OH2) precipitate formed with small addition will remain.

44
Q

What colour solution is formed when [Cu(H2O)6] ^2+ reacts with an concentrated HCl?

(Ligand substitution reaction)

A

Yellow solution (sometimes green if not complete due to blue copper ions)

[CuCl4] ^2-
(Tetrahedral)

45
Q

What’s the equation for the ligand substitution reaction when concentrated HCl is added to Cu 2+ ions ([Cu(H2O)6] ^2+) ?

A

[Cu(H2O)6] ^2+ + 4Cl- —> [CuCl4] ^2- + 6H2O

A yellow solution forms.
Only 4 Cl- ligands used as they have a larger size than water ligands.

46
Q

What colour solution is formed when [Cr(H2O)6] ^3+ reacts with an excess of NH3?

(Ligand substitution reaction)

A

Purple solution

[Cr(NH3)6] ^3+

47
Q

What colour solution is formed when [Cr(H2O)6] ^3+ reacts with an excess of NaOH (OH-)?

(Ligand substitution reaction)

A

Dark green

[Cr(OH)6] ^3-

48
Q

What happens when [Fe(H2O)6] ^3+ reacts with an excess of NH3?

(Ligand substitution reaction)

A

No change

The orange/brown Fe(OH)3 precipitate formed with the small addition of NH3/OH- remains and doesn’t dissolve.

49
Q

What happens when [Fe(H2O)6] ^3+ reacts with an excess of OH-?

(Ligand substitution reaction)

A

No change

The orange/brown Fe(OH)3 precipitate formed with the small addition of NH3/OH- remains and is insoluble.

50
Q

What happens when [Mn(H2O)6] ^2+ reacts with an excess of OH-?

(Ligand substitution reaction)

A

No change

The light brown Mn(OH)2 precipitate formed is insoluble in excess.

51
Q

What happens when [Mn(H2O)6] ^2+ reacts with an excess of NH3?

(Ligand substitution reaction)

A

No change

The light brown Mn(OH)2 precipitate formed is insoluble in excess.

52
Q

What happens when [Fe(H2O)6] ^2+ reacts with an excess of NH3?

(Ligand substitution reaction)

A

No change

The green Fe(OH)2 precipitate is insoluble in excess, however it turns brown at the surface as it’s oxidised from Fe(II) to Fe(III) to form Fe(OH)3.

53
Q

What happens when [Fe(H2O)6] ^2+ reacts with an excess of OH-?

(Ligand substitution reaction)

A

No change

The green Fe(OH)2 precipitate is insoluble in excess, however it turns brown at the surface as it’s oxidised from Fe(II) to Fe(III) to form Fe(OH)3.

54
Q

Why would green precipitate Fe(OH)2 turn orange/brown?

A

It is being oxidised by the air to form Fe(OH)3 precipitate.

55
Q

What’s happens in an Fe2+ / MnO4- reaction (in acidic conditions)?

MnO4-/Mn2+ E value = +1.33V
Fe3+/Fe2+ E value = +0.77V

(Ion colours)

A

E for MnO4- / Mn2+ is more positive than that of Fe.

Therefore Fe2+ is oxidised to Fe3+ and MnO4- is reduced to Mn2+.

Thus the purple solution (containing MnO4-) is decolourised by the orange/brown Fe2+ ions to form a colourless solution containing Mn2+ ions.

56
Q

What’s happens in an Fe3+ / I- reaction?

I2/I- E value = +0.54V
Fe3+/Fe2+ E value = +0.77V

(Ion colours)

A

The E value for iron is more positive than that of iodine.

Therefore I- is oxidised to I2 and Fe3+ is reduced to Fe2+.

This the orange/brown Fe3+ ions are reduced to pale green Fe2+ ions however this won’t be seen due to the oxidation of I- which forms iodine (which has a brown colour).

57
Q

What colour is iodine?

A

Brown

58
Q

What colour change occurs in an iron (II) / manganate (VII) reaction?

A

Purple MnO4- ions are reduced and the solution is decolourised to form a colourless solution with Mn2+ ions.

59
Q

What colour change occurs in an iron (III) / iodide reaction?

A

Orange/brown Fe3+ ions are reduced to pale green Fe2+ ions.

However his isn’t seen as iodine ions form iodine which is brown.

60
Q

What’s happens in a Cr2O7 2- / Zn reaction?

Zn 2+/Zn E value = -0.76V
Cr3+/Cr2+ E value = -0.41V
Cr2O7 2- /Cr3+ E value = +1.33V

(Ion colours)

A

Aqueous dichromate ions have an orange colour and chromium ions are green.

Zinc (strong reducing agent) can reduce the dichromate ions to Cr3+ ions (orange to green).

However, with excess zinc, they’re further reduced to Cr2+ (which is pale blue).

61
Q

What solution colour changes take place when dichromate ions react with zinc?

A

Zn is a strong reducing agent.
The orange/brown dichromate ions are reduced to green Cr3+ ions.

However, in excess zinc, they’re further reduced to pale blue Cr2+ ions.

62
Q

How can Cr3+ be oxidised to CrO4 2-?

A

Hot alkaline hydrogen peroxide is a strong oxidising agent which can oxidising Cr3+ to CrO4 2-.

(Cr oxidised +3 to +6)
(O reduced -1 in H2O2 to -2)

63
Q

How is Cu2+ reduced to Cu+?

A

A redox reaction takes place when reacted with iodide ions.

CuI and I2 are formed

I- is oxidised to iodine (brown)
Cu2+ is reduced to Cu+

The Cu+ and I- form CuI precipitate which is white however it may be masked by the iodine.

64
Q

What colour changes occur when Cu2+ is reacted with I-?

A

CuI and I2 are formed

I- is oxidised to iodine (brown)
Cu2+ is reduced to Cu+

The Cu+ and I- form CuI precipitate which is white however it may be masked by the iodine.

65
Q

What is the test for ammonium ions?

A

Aqueous NaOH is heated with the solution being tested.

If NH4+ ions are present, ammonia gas will form and turn damp red litmus paper blue.

66
Q

What’s the test for carbonates?

A

Add dilute nitric acid.

If present, there’ll be effervescence as CO2 is formed.

67
Q

What’s the test for sulfates?

A

Add barium nitrate (Ba 2+ ions)

If present, a white precipitate of barium sulphate will be formed.

68
Q

What’s the test for halides?

A

Add silver nitrate (Ag+ ions)

If present:
- Cl- will produce a white precipitate, soluble in dilute NH3

  • Br- will form a cream precipitate, soluble in concentrated NH3
  • I- will form a yellow precipitate, insoluble in concentrated NH3

Year 13 - Chemistry (12 decks)

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