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AQA A-Level Chemistry > Transition Metals > Flashcards

Transition Metals Flashcards

1
Q

What is a transition metal?

A

Metals that contain an incomplete d sub shell in at least one of their ions

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2
Q

Where are transition metals found?

A

In the ‘d block’ (middle, group 3)

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3
Q

Why are Sc and Zn technically NOT transition metals, despite being found in the d block?

A

They have no or complete d shells
Sc 3+ = [Ar] Zn 2+ = [Ar] 3d10

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4
Q

What is a ligand?

A

An atom or ion which donates a lone pair to form a co-ordinate bond to metal

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5
Q

What is a complex?

A

A metal ion with ligands co-ordinately bonded to it

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6
Q

What is the co-ordination number?

A

The number of co-ordinate bonds from ligands to the metal ion in the complex

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7
Q

What is a bidentate ligand?

A

A ligand which forms two co-ordinate bonds. Two different lone pairs on the molecule donate two electron pairs

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8
Q

Give 2 examples of a monodentate ligand

A

H2O: :OH- :NH3 :CN- :Cl

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9
Q

When can optical isomerism occur in complex molecules?

A

Can occur when bidentate ligands are attached to an octahedral complex

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10
Q

Give an example of a multidentate ligand

A

EDTA 4-, haem, [Pt(NH3)2Cl2] (cisplatin), [Ag(NH3)2]+

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11
Q

Why is EDTA 4- such an effective ligand, and what is its structure?

A

It has 6 lone pairs, and so can form 6 co-ordinate bonds with a metal ion

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12
Q

[Cu(H2O)6]2+ is added with an unknown substance. The solution turns from light blue to dark blue. What was the unknown substance?

A

Ammonia

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13
Q

Ammonia is added to [Cu(H2O)6]2+. What are the products formed?

A

[Cu(NH3)4(H2O)2]2+ + 4H2O

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14
Q

Concentrated HCl is added to [Cu(H2O)6]2+. What are the products formed?

A

[CuCl4]2- + 6H2O

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15
Q

Ammonia is added to [Cu(H2O)6]2+. What is the colour change observed?

A

Light blue to dark blue

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16
Q

Concentrated HCl is added to [Cu(H2O)6]2+. What is the colour change observed?

A

Light blue to yellow

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17
Q

Concentrated HCl is added to [Cu(H2O)6]2+. The solution should turn yellow, but it looks more green. Why?

A

Because it’s going from blue to yellow

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18
Q

Ammonia is added to [Co(H2O)6]2+. What are the products formed?

A

[Co(NH3)6]2+ + 6H2O

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19
Q

Ammonia is added to [Co(H2O)6]2+. What is the colour change observed?

A

Pink to pale brown

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20
Q

Concentrated HCl is added to [Co(H2O)6]2+. What is the colour change observed?

A

Pink to dark blue

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21
Q

Concentrated HCl is added to [Co(H2O)6]2+. What are the products formed?

A

[CoCl4]2- + 6H2O

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22
Q

Why is the colour change so dramatic when concentrated HCl is added to [Co(H2O)6]2+?

A

The colour change is dramatic because the co-ordination number also changes (Cl is big so can’t fit round octahedral)

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23
Q

What is the chelate effect and why is it feasible (refer to delta G)?

A

The substitution of monodentate ligands (eg H2O) by multidentate ligands. This happens as entropy change is positive, /\H is roughly zero and therefore /\G is negative, meaning the reaction is feasible.

24
Q

What is a use of a chelate?

A

It is useful in dealing with heavy metal poisoning, as it ‘cages’ up and so limits the poisoning effects

25
Q

What is the equation to work out the energy change, using Plank’s constant and lamda?

A

Energy = hv where h = Plank’s constant and lamda = the speed of light/wavelength

26
Q

What are the factors that affect the size of energy gap?

A

The metal, the oxidation state, the ligands, the co-ordination number

27
Q

Why are some substances able to give different colours/observations?

A

They have a variable oxidation state

28
Q

KMnO4 is titrated against acidified Fe2+. What colour change is observed?

A

Colourless to pink

29
Q

KMnO4 is used in a redox titration against acidified Fe2+. After all the acid has been used up, the colour change observed is brown/dark red rather than pink. What has happened?

A

There was not enough acid to full oxidise the MnO4-
Instead MnO2 formed

30
Q

What colour is MnO4-?

A

Purple

31
Q

A student is choosing an acid to acidify Fe2+ for a redox titration. The options are dilute H2SO4, conc H2SO4 and dilute HCl. Which acid should she choose? Give reasons why the others are unsuitable.

A

Should choose dilute H2SO4
Conc H2SO4 is an oxidising agent, but there is already an oxidising agent present
Dilute HCl - Cl could be oxidised (Cl2 gas), so the titration would larger and thus inaccurate.

32
Q

The complex ion formed in aqueous solution between cobalt (II) ions and chloride ions is a different colour from the [Co(H2O)6]2+ ion. Explain why these complexes have different colours

A

Ligands are different and so cause different d orbital splitting. This means different amounts of energy are required to promote electron to the next energy level and so different frequencies of light are absorbed. Therefore different wavelengths/colours of light are transmitted

33
Q

Fill the blanks. Heterogenous catalysts reactions often involve a ____ catalyst and _____ reactants.

A

solid catalyst and gaseous reactants

34
Q

Describe alternate pathway a heterogenous catalyst provides

A

Reactants adsorbed onto the surface (active sites)
- weakens bonds
- brings molecules closer
- more favourable orientation
Reaction occurs
Products desorbed

35
Q

What is the issue if a catalyst bonds too strongly to a reactant?

A

It will never let go - both the catalyst and reactant will be unable to take part in the reaction

36
Q

What is the issue if a catalyst bonds too weakly to a reactant?

A

If it bonds too weakly, it will not have the desired affects.

37
Q

What is the contact process and which catalyst does it involve?

A

A way of producing SO3 from SO2, and then producing sulfuric acid
Involves a vanadium (V) oxide catalyst

38
Q

Give two half equations to show the contact process

A

SO2 + V2O5 –> V2O4 + SO3
V2O4 + 1/2 O2 –> V2O5

39
Q

What is catalyst poisoning?

A

When the catalyst is covered by a substance which blocks the active sites, thus making it ineffective

40
Q

Fill in the blank. Homogenous catalysts are mostly involved in reactions in a _____ with a catalyst in a _______

A

Solution for both

41
Q

What is an autocatalyst?

A

A catalyst that is also one of the products of the reaction being catalysed.

42
Q

Give a half equation showing the reduction of manganate

A

MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O

43
Q

Give two half equations to show the reaction of iodide ions and S2O8 2- to form iodine and sulphate ions with Fe 2+ as the homogenous catalyst

A

S2O8 2- + 2Fe 2+ –> 2SO4 2- + 2Fe 3+
2I- + 2Fe 3+ –> I2 + 2Fe 2+

44
Q

Give 2 half equations to show the reaction of MnO4- with C2O4 2- which is an example of an autocatalysis reaction

A

1) 2MnO4- + 16H+ + 8Mn2+ –> 10Mn3+ + 8H2O
2) 5C2O4 2- + 10Mn3+ –> 10CO2 + 10Mn2+

45
Q

Give the formula of cisplatin

A

[Pt(NH3)2Cl2]

46
Q

How many lone pairs are there on EDTA 4-?

A

6

47
Q

Give the formula of ethanedioate

A

C2O4 2-

48
Q

Give the formula of 1,2-diaminoethane

A

AKA en
H2N-CH2-CH2-NH2

49
Q

What is a hint as to whether a complex ion is a square planar or tetrahedral?

A

Most complex ions are tetrahedral in shape, but complex ions containing Nickel, Palladium or Platinum tend to be square planar.

50
Q

Give an example of a process involving a heterogeneous catalyst

A

Contact Process, which is where V2O5 acts as a heterogeneous catalyst to allow the reactants to adsorb onto it and react.

51
Q

Give an example of a process involving a homogeneous catalyst

A

The reaction between iodide and peroxydisulfate. This is where Fe2+ acts a catalyst to allow the two negatively charged molecules to be able to react with each other.

52
Q

How does carbon monoxide poisoning arise?

A

This comes from the haemoglobin forming a stable and permanent bond with CO, meaning its useless, as opposed to H2O, O2 and CO2, which will form unstable bonds with haemoglobin.

53
Q

What is the chemical equation for the conversion of SO2 into SO3 and the regeneration of the catalyst vanadium(V) in the contact process?

A

1) SO2 (g) + V2O5 (s) -> SO3 (g) + V2O4 (s) oxdiation state of Vanadium - 5+ to 4+
2) V2O4 (s) + 1/2O2 (g) -> V2O5 (s) oxidation state of Vanadium - 4+ to 5+

54
Q

What is the chemical equation for the conversion of SO3 into H2SO4 in the contact process?

A

1) SO3 (g) + H2SO4 (l) -> H2S2O7 (s)
2) H2S2O7 (l) +H2O (l) -> 2H2SO4 (l)

55
Q

State 3 ways in which a transition metal complex can be changed to alter its colour

A
  1. change ligand
  2. change oxidation state of transition metal
  3. change coordination number

AQA A-Level Chemistry (36 decks)

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