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Chemistry > Transition metals > Flashcards

Transition metals Flashcards

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1
Q

What is special about scandium and zinc

A

They are not transition metals as their ions have either full or empty d oribtals

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2
Q

What is a transition element?

A

A d block element that forms at least 1 ion with an incomplete d sub shell

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3
Q

What is a complex ion

A

A central metal atom or ion surrounded by ligands.

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4
Q

What is a ligand?

A

A molecule or ion that can donate a pair of electrons to the transition to form a dative bond

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5
Q

What is the number of co-ordinate bonds called

A

The coordination number

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6
Q

What does monodentae mean

A

A ligand donates 1 pair of electrons to form 1 co-ordinate bonds

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7
Q

What is the convention for writing the chemical formula of a complex ion

A

Overall charge is outside the brackets
All the charges in the bracket must add to the outside bracket
[Co(H2O)5Cl]+
5 water ligands - no charge
Cl = -1
Therefore Co = 2+

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8
Q

What are the 4 characteristic properties of transition elements

A

Complex formation
Formation of coloured ions
Variable oxidation states
Catalytic activity

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9
Q

What are 3 examples of monodentae ligands

A

H2O
NH3
Cl-

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10
Q

In what way are the ligands NH3 and H2O similar

A

They are similar sizes
Both have no charge

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11
Q

Why doesnt the co-ordination number change when H2O is substituted with NH3

A

They are similar sizes

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12
Q

Can their only be 1 type of ligand on a molecule

A

No it can be incomplete
e.g. [Cu(NH3)4(H2O)2]2+

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13
Q

How big is the Cl- ligand compared to NH3 and H2O

A

It is larger

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14
Q

Can Cl- replacing H2O ligand change co-ordination number

A

Yes it can

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15
Q

What is a bidentae ligand
3 examples?

A

2 dative covalent bonds
e.g. ethane-1,2-diamine/
benzene-1,2-diol
Ethane dioate (C2O4)2-

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16
Q

What is an example of a multidentae ligand

A

EDTA 4-

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17
Q

What is Haem

A

An iron 2 complex with a multidentae ligand

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18
Q

How does oxygen attach to haem

A

it forms a co-ordinate bond with the Fe (II) enabling it to be transported in the blood)

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19
Q

Why is CO toxic

A

It replaces the oxygen co-ordinate bond

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20
Q

What is the chelate effect

A

A multidentae ligand is favourable to monodentae ligands

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21
Q

Why is the chelate effect true

A

EDTA 4- + [Cr(H2O)6]3+ —> [Cr(EDTA)]- + 6H2O
3en + [Cr(H2O)6]3+ —> [Cr(en)3]3+ + 6H2O

The multidentae ligand starts with 2 molecules on the left and 7 on the right. There has been a large change in entropy towards chaos which the universe favours

The 3 bidentae ligands start with 4 molecules on the left and 7 on the right. The entropy change in less

Enthalpy change is negligible

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22
Q

What is a common complex shape formed between small ligands and metal ions

A

An octahedral complex

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23
Q

What types of isomerism can octahedral complexes display

A

Cis-Trans isomerism with monodentae ligands
Optical isomerism with bidentae ligands

24
Q

What type of complex is formed between larger ligands and metal ions

A

Tetrahedral complexes (Cl-)
Square planar complexes (can display cis trans isomerism)

25
Q

What shape is cis platin and which isomer is it

A

Square planar
Cis isomer

26
Q

What shape does Ag+ form

A

A linear complex

27
Q

What is [Ag(NH3)2]+ used for

A

Tollens reagent

28
Q

What is the formula for tollens reagent

A

[Ag(NH3)2]+

29
Q

What are the requirements for an optical isomer

A

3 bidentae ligands
2 bidentae ligands & 2 monodentae ligands
1 hexandentae ligands

30
Q

How can transition metal oxide be identified

A

By their colour

31
Q

How does colour arise from transitions metals

A

Some of the visible light is absorbed and the remaining wave lengths of light are reflected
D electrons move from the ground state to an excited state when light is absorbed

32
Q

What is the formula for the energy difference between the ground state of electrons and their excited state

A

ΔΕ = hv
h= planks constant v= frequency
ΔΕ = hc/λ
h= planks constant c= speed of light λ= wave length (m)

33
Q

What 3 things can lead to a change in colour of a metal compound

A

Oxidation state
Co-ordination number
Change in ligand

34
Q

What is the absorption of visible light used in

A

Calorimetry

35
Q

What can a colorimeter be used for

A

Determining the conc. of coloured ions in solution

36
Q

What are the redox equations for the reduction of vanadate ions by zinc in acidic solutions

A

Zn —> Zn2+ + 2e-
VO2^+ + 2H+ +e- —> VO^2+ + H2O
2VO2^+ + 4H+ + Zn —> 2VO^2+ + 2H2O + Zn+

37
Q

C2O4 2- + MnO4- redox

A

C2O4 2- —> 2CO2 + 2e-
MnO4- + 5e- + 8H+ —> Mn2+ + 4H2O
5C2O42- + 2MnO4- + 16H+ —> 10CO2 + 2Mn2+ + 8H2O

38
Q

When does a transition metals oxidation state increase

A

In an alkaline solution

39
Q

Why do transition metals oxidation states increase in alkaline solution

A

Since oxidation is electron loss, it is easier to form negatively charged ions than a neutral or positive one

40
Q

How can low oxidation states be stabilised

A

Keep them in an acidic solution

41
Q

Fe2+ + MnO4- redox reaction

A

Fe2+ —> Fe3+ + e-
MnO4- + 5e- + 8H+ —> Mn2+ + 4H2O
5Fe2+ + MnO4- + 8H+ —> 5Fe3+ + Mn2+ + 4H2O

42
Q

What type of catalysts do transition metals act as

A

Heterogenous catalysts
Homogenous catalysts

43
Q

What is a heterogeneous catalyst?

A

A catalyst in a different phase from the reactants and the reaction occurs at the active sites in the surface

44
Q

What can be used to increase S.A of a heterogenous catalyst and reduce cost

A

Use a support medium
e.g. honey comb structure coated in platinum in catalytic converters

45
Q

What is the heterogenous catalyst used in the contact process

A

V2O5

46
Q

What is the heterogenous catalyst used in the haber process

A

Fe

47
Q

Will heterogenous catalysts last forever

A

No, they can become poisoned by impurities that block active sites.
This reduces efficiency which will cost the company

48
Q

Platinum acts as a heterogeneous catalyst in the reaction between ammonia and oxygen. It provides an alternative reaction route with a lower activation energy.
Describe the stages of this alternative route

A

Reactant(s) adsorbed onto the platinum active sites

Reaction (on the surface) or bond breaking (weakening) / bond making occurs (on the surface)

Desorption (of the product)

49
Q

What is a homogenous catalyst

A

Same phase as the reactants

50
Q

How do homogeneous catalysts work

A

The reaction proceeds through an intermediate species

51
Q

Why are variable oxidation states important in catalysis

A

Transition metals can adopt more than 1 stable oxidation state
This means they can gain and lose electrons and remain stable
Therefore they can act as both an oxidising and reducing agent in a redox reaction

52
Q

What is the contact process

A

2SO2 + O2 —> 2SO3

53
Q

What are the equations for the contact process with a V2O5 catalyst

A

SO2 + V2O5 —> SO3 + V2O4
2V2O4 + O2 —> 2V2O5

54
Q

How does Fe2+ catalyse the reaction between I- and S2O82-
(Overall and sub equation)

A

S2O8 2- + 2I- —> 2SO4 2- + I2

S2O8 2- + 2Fe2+- —> 2SO4 2- + 2Fe3+
2Fe3+ + 2I- —> 2Fe2+ + I2

55
Q

Explain what happens during autocatalysis

A

The reaction starts of slow as not much of the product (catalyst) has been formed yet
The reaction then speeds up quickly
It then slows down again at the end

56
Q

A calculation of the enthalpy of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical value than the value calculated in Question 1.2

A

Shows covalent character
Forces holding the lattice together are stronger

Chemistry (36 decks)

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