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Chemistry Unit 5 > Transition Metals > Flashcards

Transition Metals Flashcards

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1
Q

Why do transition metals have the characteristics they do?

A

They have an incomplete d sub-level.

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2
Q

Define a transition metal.

A

A metal that can form variable oxidation states with a partially filled d sub-level.

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3
Q

Give four characterisics of a transition metal.

A

1) Form complexes
2) Form coloured ions
3) Have variable oxidation states
4) Make good catalysts

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4
Q

Define a ligand.

A

An atom, ion or molecule that donates a pair of electrons to a central metal ion.

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5
Q

Define a complex.

A

A metal ion surrounded by coordinately bonded ligands.

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6
Q

What is a coordination number?

A

The number of coordinate bonds that are formed with the central metal ion.

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7
Q

Why do coordination numbers vary?

A

Due to the size of the ligand surrounding the metal ion.

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8
Q

Explain what a unidentate ligand is, and give three examples.

A

A ligand that can only donate one pair of electrons, for example, water, ammonia, or a chloride ion.

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9
Q

Explain what a bidentate ligand is, and give two examples.

A

A ligand that can donate two pairs of electrons, for example, ethane-1,2-diamine or C2O4^(2-).

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10
Q

Explain what a multidentate ligand is, and give an example.

A

A ligand that can donate more than two pairs of electrons, for example EDTA^(4-).

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11
Q

What is heam?

A

An iron(II) complex with a multidentate ligand.

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12
Q

What shape complexes and coordination number do transition metal ions form with small ligands such as water and ammonia?

A

Octohedral, 6.

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13
Q

What shape complexes and coordination number do transition metal ions form with larger ligands such as chloride ions?

A

Tetrahedral, 4.

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14
Q

What is the more irregular shape of a complex with coordination number 4? Give an example of this.

A

Square planar, cis-platin.

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15
Q

What complex does Ag+ usually form? What shape is it and what is it used for?

A

[Ag(NH3)2]^(+), linear, Tollen’s reagent.

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16
Q

Give the oxidation state and colour of (in aqueous solution) MnO4^(-).

A

+7, purple.

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17
Q

Give the oxidation state and colour of (in aqueous solution) Cr2O7^(2-).

A

+6, orange.

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18
Q

Give the oxidation state and colour of (in aqueous solution) VO2^(+).

A

+5, yellow.

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19
Q

Give the oxidation state and colour of (in aqueous solution) VO^(2+).

A

+4, blue.

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20
Q

Give the oxidation state and colour of (in aqueous solution) V^(3+).

A

+3, green.

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21
Q

Give the oxidation state and colour of (in aqueous solution) Cr^(3+).

A

+3, green/violet.

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22
Q

Give the oxidation state and colour of (in aqueous solution) Fe^(3+).

A

+3, yellow.

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23
Q

Give the oxidation state and colour of (in aqueous solution) V^(2+).

A

+2, violet.

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24
Q

Give the oxidation state and colour of (in aqueous solution) Mn^(2+).

A

+2, pale pink.

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25
Q

Give the oxidation state and colour of (in aqueous solution) Fe^(2+).

A

+2, pale green.

26
Q

Give the oxidation state and colour of (in aqueous solution) Co^(2+).

A

+2, pink.

27
Q

Give the oxidation state and colour of (in aqueous solution) Ni^(2+).

A

+2, green.

28
Q

Give the oxidation state and colour of (in aqueous solution) Cu^(2+).

A

+2, blue.

29
Q

What can change the colour of a transition metal complex?

A

A change in oxidation state, coordination number or ligand.

30
Q

Why are transition metal ions coloured?

A

Transition metal electrons in d orbitals are given energy from white light when ligands bond to them. This energy transfers electrons from the ground state to an exited state. This energy corresponds to a frequency of white light using the equation E=hv. The electron absorbes the frequency of white light, v, and we see a solution of a colour containing all the other frequencies of white light that aren’t absorbed by the electron.

31
Q

Describe the process of using spectroscopy to measure the concentration of coloured ions in a solution.

A

Using a range of known concentrations, we shine white light through a filter, which is chosen only to let through the colour of light that we know to be absorbed by the sample, and then through the sample and onto a colorimeter. We then plot a calibration graph of concentration against relative absorbance, and we can then use this to read off the concentration of an unknown sample.

32
Q

How can we produce Cr^(3+) and Cr^(2+) ions from dichromate(VI) ions? Give the two equations for this and state the two colour changes.

A 
Reducing it with zinc and a dilute acid.
Cr2O7^(2+) + 14H^(+) + 3Zn --> 3Zn^(2+) +2Cr^(3+) + 7H2O
This changes from orange to green.
2Cr^(3+) + Zn --> Zn^(2+) + 2Cr^(2+)
This changes from green to blue.
33
Q

Give the oxidation state and colour of Cr^(2+).

A

+2, blue.

34
Q

Give the oxidation state and colour of (in aqueous solution) CrO4^(2-).

A

+6, yellow.

35
Q

What is the equation for the redox titration of Fe^(2+) with MnO4^(-) in acid solution?

A

MnO4^(-) + 8H^(+) + 5Fe^(2+) –> Mn^(2+) + 4H2O +5Fe^(3-)

36
Q

What is the equation for the redox titration of Fe^(2+) with Cr2O7^(2-) in acid solution?

A

Cr2O7^(2-) + 14H^(+) + 6Fe^(2-) –> 2Cr^(3+) + 7H2O + 6Fe^(3+)

37
Q

Give the three equations and respective colours for the oxidation of Co^(2+) to Co^(3+) with air in an ammoniacal solution.

A

[Co(H2O)6]^(2+) + 2NH3 –> [Co(H2O)4(OH)2] + 2NH4^(+)
This changes from a pink solution to a blue precipitate.
[Co(H2O)4(OH)2] + 6NH3 –> [Co(NH3)6]^(2+) 4H2O + 2OH^(-)
This changes from a blue precipitate to a straw coloured solution.
[Co(NH3)6]^(2+) + air –> [Co(NH3)6]^(3+)
This changes from a straw coloured solution to a dark brown solution.

38
Q

How can we oxidise Cr^(3+) ions? Give the equation for this reaction and state any colour changes.

A

Hydrogen peroxide in alkaline solution.
2Cr^(3+) + 10OH^(-) + 3H2O2 –> 2CrO4^(2-) + 8H2O
This changes from a green solution to a yellow solution.

39
Q

How can we oxidise Co^(2+) ions? Give the equation for this reaction and state any colour changes.

A

Hydrogen peroxide in alkaline solution.
2Co^(2+) + H2O2 –> 2Co^(3+) + 2OH^(-)
This changes from a pink solution to a dark brown precipitate.

40
Q

What is a heterogeneous catalyst?

A

A catalyst that is not in the same phase as the reactants, and the reaction occurs at the surface of it.

41
Q

Why are support mediums used?

A

To maximise the surface area of a heterogeneous catalyst. This increases the number of molecules that can react at the same time, therefore increasing the rate of reaction. This also minimises the cost of using the catalyst, as only a thin layer of it is needed.

42
Q

Give an example of a support medium and where it is used.

A

A ceramic lattice in a catalytic converter is used as a support medium for Rh or Pt.

43
Q

Give equations to demonstrate how V2O5 acts as a catalyst in the contact process.

A

V2O5 + SO2 –> V2O4 + SO3
The reduced catalyst is then oxidised by oxygen gas back to it’s original state.
2V2O4 + O2 –> 2V2O5
The overall equation is: 2SO2 + O2 –> SO3

44
Q

What is the catalyst used in the manufacture of

methanol from carbon monoxide and hydrogen? Give an equation for this reaction.

A

Cr2O3.

CO + 2H2 –> CH3OH

45
Q

What is the catalyst used in the Haber Process? Give an equation for this reaction.

A

Iron.

N2 + 3H2 –> 2NH3

46
Q

Why must we avoid impurities when using catalysts?

A

Impurities can poison a catalyst by binding itself onto the surface and block reactants from being absorbed. This reduces the surface area and slows down the reaction time, reducing its efficiency. This can increase the cost of a chemical process by decreasing the amount of product made in time and energy constraints, or the catalyst may have to be replaced or regenerated.

47
Q

What is a homogeneous catalyst?

A

A catalyst in the same phase as the reactants, that forms an intermediate species that requires a lower activation energy than is needed to make the products directly from the reactants.

48
Q

What is the test for iodine?

A

Starch will turn iodine blue-black.

49
Q

Name the catalyst and give the half equations and overall equation for the reaction between iodide ions and peroxodisulfate ions.

A

Catalyst: Fe^(2+).
S2O8^(-) + Fe^(2+) –> Fe^(3+) + 2SO4^(2-)
Fe^(3+) + 2I^(-) –> I2 + Fe^(2+)
Overall: S2O8^(-) + 2I^(-) –> 2SO4^(2-) + I2

50
Q

Why does the reaction between iodide ions and peroxodisulfate ions need a catalyst?

A

They are both negatively charges ions so will repel each other, so it’sunlikely they will collide and react.

51
Q

What is an autocatalysis reaction?

A

A reaction in which a product formed then acts as a catalyst for the reaction. This means that the reaction speeds up with time due to the amount of product increasing.

52
Q

Why are variable oxidation states important in a catalyst?

A

They can gain or lose electrons in their d orbitals, meaning they can easily transfer electrons to speed up reactions.

53
Q

Give the reaction for C2O4^(2-) with MnO4^(-) and identify the catalyst.

A

2MnO4^(-) + 16H^(+) + 5C2O4^(2-) –> 2Mn^(2+) + 8H2O + 10CO

The catalyst is Mn^(2+).

54
Q

What is the transition metal ion in haemoglobin, what is its job, and how does it work?

A

Fe(II). The job of haemoglobin is to transport oxygen around the body through the blood. In the lungs, a water ligand is substituted for an oxygen molecule. When oxyhaemoglobin reaches a place where oxygen is needed, the oxygen molecule is exchanged for a water ligand.

55
Q

What can poison haemoglobin, and how does it achieve it?

A

Carbon monoxide. CO substitutes a water ligand on haemoglobin, but it is such a strong ligand that it won’t exchange with oxygen or water ligands, so the haemoglobin cannot transport oxygen any more.

56
Q

What is the transition metal ion in cisplatin?

A

Pt(II).

57
Q

What is cisplatin used for?

A

It is an anticancer drug - it prevents cancer cells from reproducing.

58
Q

Explain some of the benefits and risks associated with cisplatin.

A

Although it can prevent cancer cells reproducing, it can also stop other cells from reproducing, resulting in hair loss, and a weakened immune system, which increases the risk of infection. It can also cause kidney damage.

59
Q

What is the complex ion in Tollen’s reagent, what is its shape, and what is it used for?

A

[Ag(NH3)2]^(+), linear, to distinguish between aldehydes and ketones. It will form Ag in the form of a silver mirror when reacted with an aldehyde.

60
Q

Give the shape of cisplatin.

A

Square planar.

Chemistry Unit 5 (5 decks)

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