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A-level Chemistry > 23 - The transition metals > Flashcards

23 - The transition metals Flashcards

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1
Q

Define a transition metal.

A

An element which gives an ion or atom with an incomplete d sub-level

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1
Q

Give the four characteristics of transition metals.

A
  • Complex formation
  • Variable oxidation states
  • Formation of coloured ions
  • Catalytic activity
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2
Q

Define a ligand.

A

A molecule or ion which forms a co-ordinate bond with a transition metal by donating a pair of electrons.

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3
Q

Define a complex.

A

A central metal atom or ion surrounded by ligands.

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4
Q

Define co-ordination number.

A

Number of co-ordinate bonds to the central metal atom or ion.

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5
Q

Give three monodentate ligands.

A

H2O, NH3, Cl-

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6
Q

Compare the size and charges of Cl-, NH3 and H2O.

A
  • Cl- is larger than NH3 and H2O
  • NH3 and H2O are non-charged, whereas Cl- is negative
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7
Q

Give two bidentate ligands.

A
  • H2NCH2CH2NH2 (ethandiamine)
  • C2O4 2-
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8
Q

Give a multidentate ligand.

A

EDTA 4-

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9
Q

What is haem?

A

Iron (II) complex with a multidentate ligand.

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10
Q

How is haemoglobin formed?

A

Oxygen forms a co-ordinate bond to Fe (II) in haemoglobin, which allows oxygen to be carried in the blood.

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11
Q

Why is CO toxic?

A

Replaces oxygen co-ordinately bonded to Fe (II) in haemoglobin.

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12
Q

Describe and explain the chelate effect.

A
  • Multidentates replace bidentates which replace monodentates.
  • This is because the entropy is increased
  • Complex + multidentate –> Complex + 6 monodentates
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13
Q

What shape do complexes with small ligands commonly form?

A

Octahedral –> it’s like 6 bonding pairs but they’re ligands instead

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14
Q

What forms of isomerism are displayed by octahedral complexes?

A
  • Monodentates –> cis-trans isomerism
  • Bidentates –> optical isomerism
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15
Q

What shape do complexes with larger ligands, such as Cl-, commonly form?

A

Tetrahedral

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16
Q

Give the formula of the complex found in Tollen’s reagent.

A

[Ag(NH3)2]+

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17
Q

What shape does cisplatin form?

A

Square-planar

18
Q

How does colour arise?

A

Some light is absorbed, some is reflected/transmitted.
When light is absorbed, d electrons move from ground state to excited state.

19
Q

Give the equation for the difference in energy between ground state and excited state.

A

E change = hv = h(c/lamda)

h = Planck’s constant
v = frequency (units s-1)
c = speed of lights (m s-1
lamda = wavelength of absorbed light (m)

20
Q

What causes a colour change?

A

Change in oxidation state
Change in co-ordination number
Type of ligand

21
Q

Describe the process of spectroscopy.

A

Add an appropriate ligand to intensify colour
*Make up solutions of known concentration
*Measure absorption or transmission
*Plot graph of absorption vs concentration
*Measure absorption of unknown and compare

22
Q

How is Vanadium (V) reduced by the addition of acidified zinc?

A

VO2^+ (5) –> VO^2+ (4) –> V^3+ (3) –> V^2+ (2)

23
Q

What colours are vanadium ions?

A

5+ is yellow
4+ is blue
3+ is green
2+ is violet

24
Q

What is the redox potential for a transition metal ion changing from a higher to lower oxidation state influenced by?

A

The redox potential for a transition
metal ion changing from a higher to a
lower oxidation state is influenced by
pH and by the ligand.

25
Q

Give half equations equations for the use of Tollen’s reagent to distinguish between ketones and aldehydes.

A

Red: [Ag(NH3)2]+ + e- –> Ag + 2NH3
Oxi: CH3CHO + H2O –> CH3CO2H + 2H+ + 2e-

26
Q

Give the ionic equation between MnO4- and Fe2+ in a titration.

A

MnO4- + 8H+ + 5Fe2+ –> MN2+ + 4H2O + 5Fe3+

27
Q

Give the overall equation for the reaction between MnO4- and ethanedioate.

A

2MnO4- + 16H+ + 5C2O4- –> 10CO2 + 2Mn2+ + 8H2O

28
Q

Give two types of catalyst.

A
  • Homogenous
  • Hetrogenous
29
Q

What is a hetrogenous catalyst?

A

Different phase from the reactant

30
Q

Where do reactions involving a hetrogenous catalyst occur?

A

On the surface of the solid catlyst

31
Q

What is a support medium, and how does it work?

A

A support medium increases the surface area of a solid catalyst. For example, the usage of a Rb catlyst supported on a hexagon frame to increase SA.

32
Q

Give equations to describe the use of vanadium as a catalyst in the Contact Process.

A
  1. SO2 + V2O5 –> SO3 + V2O4
  2. 2V2O4 + O2 –> 2V2O5
    Overall: 2SO2 + O2 –> 2SO3
33
Q

Which process does Fe (II) catalyse?

Name, equation, type of catalyst

A

Haber
N2 + 3H2 –> 2NH3
Hetrogenous

34
Q

What is catalytic poisoning?

A

Hetrogenous catalysts active sites are blocked by impurities
Activity reduced
Cost implication

35
Q

Define a homogenous catalyst.

A

Same state as reactants

36
Q

How do hetrogenous catalysts work?

A

Reaction proceeds through an intermediate species. That being the catlysts will be changed oxidation state, and then reform its original oxidation state.

37
Q

Give equations to explain how Fe2+ catalyses the reaction between I- and S2O8^2-.

A

S2O8^2- + 2Fe2+ –> 2SO4^2- + 2Fe3+
2I- + 2Fe3+ –> 2Fe2+ + I2

38
Q

Define autocatalysis.

A

One of the products of the reaction can act as a catalyst and increases the rate of reaction.

39
Q

Give the equations for the reaction of MnO4- and C2O4-, including autocatalysis using Mn2+.

A
  1. 4Mn2+ + MnO4- + 8H+ –> 5Mn3+ + 4H2O
  2. 2Mn3+ + C2O4- –> 2Mn2+ + 2CO2
40
Q

Why are some reactions very slow? (2)

Specifically two negative ions

A
  1. Negative ions repel
  2. Increases activation energy
41
Q

Explain why an aqueous solution containing [Fe(H2O)6]3+ ions has a lower pH than an aqueous solution containing [Fe(H2O)6]2+ ions. (4)

A

Fe3+ has a greater charge density
Fe3+ ions polarise water molecules more
O-H bond in water ligands is weakened
More H+ ions are released

42
Q

How does a hetrogenous catalyst work?

A

Reactants adsorb onto surface
Weakens bonds
Products desorb from surface

A-level Chemistry (34 decks)

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