Transition Metals

Question 1

What are the characteristics of a transition metal

Answer 1

•complex formation,
•formation of coloured ions,
•variable oxidation state
•catalytic activity.

incomplete d sub-level in atoms or ions

Question 2

Why is zinc not a transition metal

Answer 2

Zinc can only form a +2 ion.

In this ion the Zn2+ has a complete d orbital and so does not meet the criteria of having an incomplete d orbital in one of its compounds.

Question 3

What is a complex

Answer 3

is a central metal ion surrounded by ligands.

Question 4

What is co ordinate bonding

Answer 4

Co-ordinate bonding is involved in complex formation.
Co-ordinate bonding is when the shared pair of electrons in the covalent bond come from only one of the bonding atoms

Question 5

What is a ligand

Answer 5

an atom, ion or molecule which can donate a lone electron pair.

Question 6

Examples of monodentate ligand

Answer 6

e.g. H2O, NH3 and Cl- )

Question 7

Examples of monodentate ligand

Answer 7

e.g. H2O, NH3 and Cl- )

Question 8

What is a monodentate ligand

Answer 8

Only forms one coordinate bond per ligand

Question 9

Describe Bidentate ligand

Answer 9

NH2CH2CH2NH2 and ethanedioate ion C2O4 2- )

which have two atoms with lone pairs and can form two coordinate bonds per ligand,

Question 10

What is a multi dentate ligand

Answer 10

multidentate (e.g. EDTA4- which can form six coordinate bonds per ligand).

Question 11

Describe substitution reactions for NH3 and H2O

Answer 11

The ligands NH3 and H2O are similar in size and are uncharged.
Exchange of the ligands NH3 and H2O occurs without change of co-ordination number

[Co(H2O)6]2+(aq) + 6NH3 (aq) -> [Co(NH3)6]2+(aq) + 6H2O (l

Question 12

Describe the reaction of chloride ions

Answer 12

The Cl- ligand is larger than the uncharged H2O and NH3 ligands so therefore ligand exchange can involve a change of co-ordination number.

Question 13

Describe the chelate effect

Answer 13

The substitution of minodentate ligand with bidentate or multidentate ligand leads to a more stable complex

Can be explained in terms of positive entropy change as there are molecules of products than reactants

Question 14

What is EDTA used for

Answer 14

Added to rivers to remove poisonous heavy metal ions as the EDTA complexes are not toxic

Question 15

How does colour change arise

Answer 15

Change in
1. Oxidation state
2. Coordination number
3. Ligand

Question 16

How does colour arise in transition metals

Answer 16

Electronic transitions from the ground state to excited states

1. A portion of visible light is absorbed
2. This promotes d electrons to a higher energy level
3. Light that is not absorbed is transmitted to give the substance colour

Question 17

Equation for colour

Answer 17

/\E= hv

/\E=hc/ y

Question 18

What element doesn’t have colour

Answer 18

Scandium

Question 19

what are the relative trends for transition metals as oxidising agents

Answer 19

*Relative stability of +2 state with respect to +3 state increases
across the period
*Compounds with high oxidation states tend to be oxidising agents
e.g. MnO4
- *Compounds with low oxidation states are often reducing agents e

Question 20

what are the main oxidaion states for vanadium

Answer 20

VO2+ Oxidation state +5 ( a yellow solution)
VO^2+ Oxidation state + 4 (a blue solution)
V^3+Oxidation state + 3 (a green solution)
V^2+Oxidation state + 2 (a violet solution)

Question 21

what is tollens reagent

Answer 21

[Ag(NH3)2]+
is used in Tollens’ reagent to distinguish between aldehydes
and ketones

Question 22

what is half equation for manganate

Answer 22

MnO4-(aq) + 8H+
(aq) + 5Fe2+ (aq) –> Mn2+ (aq) + 4H2O (l) + 5Fe3+

Question 23

what is half equation for ethanedioate

Answer 23

C2O42- –>2CO2 + 2e-

Question 24

what is a heterogenous catalyst

Answer 24

A heterogeneous catalyst is in a different phase from the reactants

Question 25

Describe adsorption

Answer 25

Adsorption of reactants at active sites on the
surface may lead to catalytic action.
The active site is the place where the reactants adsorb onto the
surface of the catalyst.
This can result in the bonds
within the reactant molecules becoming weaker

There will also be a higher concentration of reactants
at the solid surface, so leading to a higher collision
frequency.

Question 26

what is the process of heterogeneous catalyst

Answer 26

1.Reactants form bonds with atoms at active sites on
the surface of the catalyst (adsorbed onto the
surface)
2. As a result bonds in the reactants are weakened
and break
3. New bonds form between the reactants held close
together on catalyst surface.
4. This in turn weakens bonds between product and
catalyst and product leaves (desorbs).

Question 27

how is V2O5 a catalyst in the Contact process.

Answer 27

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

Question 28

what is a homogeneous catalyst

Answer 28

a catalyst which is in the same phase as the reactants

Question 29

how does Fe speed up the reaction

Answer 29

The uncatalysed reaction is very slow because the reaction
needs a collision between two negative ions.
Repulsion between the ions is going to hinder this – meaning high
activation energy

the Fe reduces repulsion between negatively charged ions

Question 30

How can transition metals be homogeneous catalyst

Answer 30

because they can form various oxidation states.

They are able to donate
and receive electrons and are able to oxidize and reduce.

This is because the ions contain partially filled sub-shells of d
electrons that can easily lose or gain electrons.

Question 31

what are the half equations for the homogeneous catalysts

Answer 31

stage 1
S2O82- + 2Fe2+ –> 2SO4 2- + 2Fe3+

stage 2
2I- + 2Fe3+ –> 2Fe 2+ + I2

Question 32

what is autocatalysis

Answer 32

autocatalysis where one of
the products of the reaction can catalyse the
reaction.

Question 33

what are the half equations for autocatalysis

Answer 33

Step 1 4Mn2+ + MnO4
- + 8 H+–> 5Mn3+ + 4 H2O
Step 2 2Mn3+ + C2O4 2- –> 2Mn2+ + 2 CO2

Question 34

how does Mn2+ act as an autocatalysis

Answer 34

The initial uncatalysed reaction is slow because the reaction is a
collision between two negative ions

which repel each other
leading to a high activation energy.
The Mn2+ ions produced act as an autocatalyst and therefore the reaction starts to speed up because they bring about the
alternative reaction route with lower activation energy.