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A Level Chemistry > 3.2.5 Transition Metals > Flashcards

3.2.5 Transition Metals Flashcards

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1
Q

Explain the chelate effect

A

Bidentate and multidentate ligands replace monodentate ligands from complexes
Increase in number of species present so increase in entropy

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2
Q

What causes colours of transition metals

A

Colour arises when some of the wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected.
d electrons move from the ground state to an excited state when light is absorbed.

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3
Q

What causes change in colour of transition metal complexes

A

Change in oxidation state, co-ordination number and ligand alter change E

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4
Q

What causes Vanadium species in oxidation states IV, III and II

A

Reduction of V ions by zinc in acidic solution

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5
Q

What influences redox potential for a transition metal ion changing from high to lower oxidation state

A

pH and the ligand

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6
Q

Heterogeneous catalyst

A

In different phase from the reactants and the reaction occurs at active sites on the surface

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7
Q

Homogeneous catalyst

A

In the same phase as reactants. When catalyst and reactants are in the same phase, the reaction proceeds through an intermediate species

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8
Q

The contact process reactions

A

SO2 + V2O5 —> SO3 + V2O4 (redox)
2V2O4 + O2 —> 2V2O5
Overall : 2SO2 + O2 <=> 2SO3
Each step has lower activation energy than one step reaction

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9
Q

Catalyst in contact process

A

V2O5 acts as heterogeneous catalyst

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10
Q

Catalyst in Haber process

A

Fe used as heterogeneous catalyst
Pea size lumps to increase surface area

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11
Q

Heterogeneous catalyst negatives

A

Can be poisoned by impurities that block active sites

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12
Q

How do Fe2+ ions catalyse the reaction between I− and S2O82–

A

S2O82- (aq) + 2I-(aq) → 2SO42-(aq) + I2(aq)
Aqueous iron(II) ions catalyse the reaction:
Step1: S2O82-(aq) + 2Fe2+(aq) → 2SO42-(aq) + 2Fe3+(aq)
Step2: 2Fe3+(aq) + 2I-(aq) → 2Fe2+(aq) + I2(aq)

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13
Q

How do Mn2+ ions autocatalyse the reaction between C2O42– and MnO4–

A

2MnO4-(aq) + 16H+(aq) +5C2O42-(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(l)
Step1: 4Mn2+(aq) + MnO4-(aq) + 8H+(aq) → 5Mn3+(aq) + 4H2O(l)
Step2: 2Mn3+(aq) + C2O42-(aq) → 2CO2 (g) + 2Mn2+(aq)

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14
Q

State what is meant by the term bidentate ligand.

A

Two atoms or two points of attachment
Each donating a lone electron pair

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15
Q

Define coordinate bond

A

A shared electron pair or a covalent bond
Both electrons from one atom

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16
Q

Meaning of the term autocatalytic

A

Product of the reaction acts as a catalyst

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17
Q

4 oxidation states of vanadium + ion colours

A

+5 (VO2^+) yellow
+4 (VO^2+) blue
+3 (V^3+) green
+2 (V^2+) violet

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18
Q

Describe the characteristic properties of the elements titanium to copper + explain in terms of electronic structure

A

Variable oxidation states
Catalysts
Form complex ions
Form coloured compounds
Transition elements are d-block elements which form one or more stable ions with an incomplete d subshell

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19
Q

Define ligand

A

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

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20
Q

Define co-ordinate bond

A

A covalent bond where both electrons come from the same atom

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21
Q

Define co-ordination number

A

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

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22
Q

Describe the origin of the colour of a transition metal complex ion

A

Colour arises when some of the wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected

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23
Q

Describe how the concentration of iron(ii) ions in aqueous solution can be found

A

Titrating with either potassium manganate(VII) solution or potassium dichromate(VI) solution

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24
Q

Describe how heterogeneous catalysts can be made more efficient

A

Make the particles as small as possible to increase surface area

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25
Q

Explain how a homogeneous catalyst works

A

The catalyst forms an intermediate with the reactant with a lower activation energy. The intermediate often has a different oxidation state to the original transition metal. At the end of the reaction the original oxidation state will reoccur.

26
Q

D-block elements not classed as transition metals

A

Scandium- only forms 3+ ion- no electrons in 3d sub shell
Zinc- only forms 2+ ion- complete 3d sub shell

27
Q

Define complex

A

central metal atom or ion surrounded by ligands

28
Q

What complexes are formed when a solution of ammonium vanadate(V) (NH4VO3) is reduced by zinc metal in acid conditions

A

[VO2(H2O)4]^+
[VO(H2O)5]^2+
[V(H2O)6]^3+
[V(H2O)6]^2+

29
Q

State the observations when Na2CO3(aq) is added to a solution containing
[Al(H2O)6]3+(aq) ions

A

White ppt
Bubbles/effervescence

30
Q

What are some characteristic physical properties of transition metals

A

Metallic, good conductors of heat and electricity, hard, shiny, high melting + boiling, low reactivity

31
Q

Uses of iron

A

Vehicle bodies, to reinforce concrete

32
Q

Uses of titanium

A

Jet engine parts

33
Q

Uses of copper

A

Water pipes

34
Q

Give some examples of transition metals catalysts and the processes/reactions they catalyse

A

Iron- Haber process
Vanadium (V) oxide - Contact process
MnO2 - decomposition of H2O2

35
Q

Which electrons do transition metals lose first when forming ions

A

4s

36
Q

Define the term multidente ligand

A

A ligand that forms 3 or more co-ordinate bonds to the central metal ion

37
Q

How many co-ordinate bonds does EDTA^4- form

A

6

38
Q

Shape of platin (cisplatin)

A

Square planar
4 ligands (breaks rule)

39
Q

What conditions are needed for a complex ion to display optical isomerism

A

Usually octahedral molecules with 2 or more bidente ligands
Mirror images are non-superimposable

40
Q

What happens to Co^2+, Cu^2+, Fe^3+ coordination numbers when Cl^- ligands replace NH3/H2O ligands

A

Decrease from 4 to 6 as Cl^- much larger ligand

41
Q

What is haem’s metal ion, coordination number and ligands

A

Molecule that makes up protein chains
Fe^2+ central metal ion
Coordination number 6
4 bonds are to a ring system called porphyrin
1 is to nitrogen of a glob in molecule
1 is to oxygen of O2 molecule

42
Q

How does haemoglobin transport oxygen

A

O2 forms weak coordinate bond to the metal ion
Transported around the body
Bond breaks when haemoglobin reaches cells and oxygen is released

43
Q

Why is CO toxic

A

Coordinately bonds to Fe^2+ and is a better ligand
Stops O2 from bonding and being transported around body

44
Q

What can you use to reduce Vanadium

A

Zinc

45
Q

What does a colorimeter do

A

Measures the absorbance of a particular wavelength of light by a solution

46
Q

Why can transition metals have variable oxidation states

A

Have partially filled d-orbitals so can lose 4s and 2d electrons

47
Q

When oxidation state is high, how do transition metals exist

A

Covalently bond to other species
After oxidation state of around 3

48
Q

What colour is MnO4^-

A

Deep purple

49
Q

What colour is Mn^2+

A

Pink

50
Q

What colour is Cr2O7^2- and Cr^3+

A

Orange
Green

51
Q

What happens to aqua metal ions in acidic conditions and alkaline conditions

A

Reduced acid
Oxidised alkaline

52
Q

What metals are used in catalytic converted and which reactions do they catalyse

A

Pt, Rd, Pd
2CO + 2NO —> 2CO2 + N2
Alkane + oxygen —> H2O + CO2

53
Q

How do heterogeneous catalysts work

A

Reactants adsorb to the catalyst’s surface at active sites
Weakens bond within reactants + hold them close together on surface
Once reaction has occurred, products desorb from active sites

54
Q

What properties make a good catalyst

A

Can’t adsorb too strongly as products won’t desorb
Can’t adsorb too weakly as reactant wouldn’t be held in place long enough and bonds wouldn’t be sufficiently weakened

55
Q

How to increase efficiency of heterogeneous catalysts

A

Increase surface area
Spread onto inert support medium like ceramic honeycomb or mesh

56
Q

What is catalyst poisoning

A

Unwanted impurities adsorb to catalyst’s active sites and don’t desorb

57
Q

How can catalyst be degraded other than impurities poisoning

A

Finely divided catalysts can be gradually lost from their support medium

58
Q

How long does catalyst in Haber process last + what is it poisoned by

A

5 years
Sulphur impurities

59
Q

Why does the reaction between S2O8^2- ions and I^- ions have high activation energy

A

2 negative ions
Repel each other

60
Q

Conc of reactant against time graph for auto catalysed reaction shape

A

Initially show - not much catalyst formed
Rate increases as catalysts made
Slows down as reactants are used up

61
Q

How can you monitor the concentration of MnO4^- ions

A

Colorimeter

A Level Chemistry (36 decks)

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