transition metals

Question 1

What is a transition metal?

Answer 1

A metal that can form one or more stable ions with an incomplete d sub-level

Question 2

What is the electron configuration of:
Ti
V
Cr
Mn
Fe
Co
Ni
Cu?

Answer 2

Ti: [Ar]3d2,4s2
V: [Ar]3d3,4s2
Cr: [AAr]3d5,4s1
Mn: [Ar] 3d5,4s2
Fe: [Ar] 3d6,4s2
Co: [Ar] 3d7,4s2
Ni: [Ar] 3d8, 4s2
Cu: [Ar] 3d10, 4s2

Question 3

Why are Scantium and zinc not transition metals?

Answer 3

As their stable ions don’t have incomplete d sub-levels
-Sc3+ has an empty d sub level
-Zn2+ has a full d sub level

Question 4

What are the physical properties of the transition metals?

Answer 4

High density
High melting and boiling points

Question 5

What are the chemical properties of transition metals?

Answer 5

Form complex ions
Form coloured ions
Good catalysts
Exist in variable oxidation states

Question 6

What is a complex ion?

Answer 6

A metal ion surrounded by co-ordinately bonded ligands

Question 7

Define co-ordinate bond and ligand:

Answer 7

Co-ordinate bond: covalent bond in which both electrons in shared pair come from same atom
Ligand: an atom, ion or molecule that donates a pair of electrons to a central metal ion

Question 8

Define monodentate, multidentate and bidentate:

Answer 8

Mono- only form one co-ordinate bond
Bi- form two co-ordinate bonds
Multi- more than one co-ordinate bonds

Question 9

Define Lewis base and Lewis acid:

Answer 9

Base- lone pair donor
Acid- lone pair acceptor

Question 10

What shape is a complex with a co-ordination number of 2?

Answer 10

Linear, common with Ag+ complex

Question 11

What is the shape of a complex with co-ordination number of 4?

Answer 11

Square planar with Pt2+ and Ni2+ complexes

Tetrahedral with larger ligands (e.g Cl-) as too big for 6 to fit

Question 12

What is the shape of a complex with a co-ordination number of 6?

Answer 12

Octahedral, common with small ligands (e.g H2O and NH3)

Question 13

What is the structure of haemoglobin?

Answer 13

4 Fe2+ centres, each with a porphyrin ligand, taking up 4 of the 6 co-ordination sites
One of the other four sites is bonded to the rest of haemoglobin leaving one site free for oxygen to bond

Question 14

Why do CO and CN- bond to haemoglobin instead of O2?

Answer 14

O2 is not a particularly good ligand and so easily comes off the iron
CN- and CO are better ligands and so bond in preference to O2. This is why they’re toxic as prevent the transport of O2 around the body

Question 15

What is a ligand substitution reaction?

Answer 15

Where one ligand is replaced by another ligand

Question 16

What is partial substitution?

Answer 16

When only some of the ligands are replaced

Question 17

What happens when ligands are substituted by smaller/bigger ligands?

Answer 17

Co-ordination number may change.
If bigger ligands, then fewer fit round molecule

Question 18

What is the Chelate effect?

Answer 18

Substitution of unidentate ligands with bi- or multidentate ligands leads to a more stable complex because reaction results in an increase in entropy

Question 19

What are ligands that form more than one co-ordinate bond sometime called?

Answer 19

Chelating agents as very good at bonding to metal ion and very difficult to remove so renders the metal ion harmless, e.g. EDTA4-

Question 20

Why are reactions where ligands are replaced by those that form more co-ordinate bonds feasible?

Answer 20

because ∆H is negligible and ∆S very positive so ∆G is very negative and reaction is feasible

Question 21

Why do electrons in transition metals absorb UV/visible light?

Answer 21

To provide energy to promote electrons to higher energy levels

Question 22

What is the equation to measure gap in energy?

Answer 22

∆E = hf = hc ÷ λ

Where h=plancks constant
F= frequency of light
C=velocity of light
λ= wavelength of light

Question 23

Why are transition metals compounds coloured?

Answer 23

The light seen is a mixture of the colours that are not absorbed when visible light is absorbed to excite electrons to higher energy level (the light reflected (solids) or transmitted (solution) )

Question 24

What are the factors which affect colour?

Answer 24

Identity of metal
Oxidation state of metal
Identity of ligands
Co-ordination number

Question 25

How does UV/visible spectroscopy work?

Answer 25

Frequencies at which a complex absorbs uv/vis light can be measured with a UV/visible light spectrometer UV/visible light passed through complex and frequencies of UV/vis passing through detected The more conc. the solution, the more light that’s absorbed

Question 26

Why are ligands added to some ions for colorimetry?

Answer 26

The colour would be too weak so ligand intensifies the colour as otherwise machine wouldn’t detect well

Question 27

What conditions are better for oxidising/reducing transition metals?

Answer 27

Oxidise- alkaline conditions Reduce- acidic conditions

Question 28

Why do ligands affect how easy it is to reduce transition metals compounds?

Answer 28

Different ligands have different attractions to the central ion, and could also be affected by shape

Question 29

What are the colours of the different oxidation states if vanadium?

Answer 29

V(+5) e.g VO2 + - yellow V(+4) e.g VO 2+ - blue V(+3) e.g. V 3+ - green V(+2) e.g. V 2+ - violet

Question 30

What conditions are used to reduce vanadium?

Answer 30

Acidic conditions using Zinc as reducing agent

Question 31

What transition metal complex is used in redox titrations and what conditions?

Answer 31

Potassium manganate (VII) as contains MnO4- ion dilute sulfuric acid as needs acidic conditions

Question 32

Why are other acids not used?

Answer 32

HCl- as MnO4- would also oxidise Cl- to Cl2 so would affect volume of KMnO4 needed Conc. sulfuric and conc. nitric cannot be used as they are oxidising agents so would affect volume of KMnO4 needed Ethanoic acid cannot be used as it is weak and would not provide enough H+

Question 33

What’s the ratio for titrating Fe2+ with KMnO4, and what do you do if iron not in +2 oxidation states?

Answer 33

5:1 If Fe(0) react with sulfuric acid If Fe(3+) react with zinc

Question 34

What is the ratio of C2O4 2- to MnO4- in a titration, and why does the reaction require warming?

Answer 34

5:2 Both ions are negative and so repel each other and need warming for reaction to proceed, however once Mn2+ produced, it acts as catalyst so speeds up (auto catalysis)

Question 35

What is a catalyst and how do they work?

Answer 35

Substance that increases the rate of reaction but is not used up Provide an alternative route with lower activation energy

Question 36

What is a heterogenous catalyst and how does it work?

Answer 36

Catalyst is in different phase to reactants, so usually solid and reaction takes place on surface At least one reactant is adsorbed onto surface at active sites which: A. Concentrates reactants so increases likelihood of collision B. May weaken some bonds in molecule C. Position molecule in favourable orientation

Question 37

What happens if adsorption is: A. Too strong? B. Too weak?

Answer 37

Too strong: molecules unable to move around active sites so less likely to meet another reactant too weak: not many molecules adsorbed so the catalyst will have very little effect

Question 38

How is surface area maximised to save costs?

Answer 38

Using very thin coating on some sort of support medium (e.g honeycomb structure)

Question 39

What is catalyst poisoning and what effect does this have?

Answer 39

Other substances adsorb strongly onto surface Lowers efficiency of catalyst or makes it completely useless Very difficult to remove so very costly.

Question 40

What is the catalyst for the contact process?

Answer 40

V2O5 (vanadium (V) oxide)

Question 41

What is a homogenous catalyst and how does it work?

Answer 41

In same state as reactants (usually in solution) and proceed via intermediate species (reactant and catalyst) which then reacts further and regenerates catalyst

Question 42

What property of transition metals allows them to act as catalysts?

Answer 42

Able to vary oxidation states

Question 43

What are metal aqua ions?

Answer 43

Metal ions surrounded by 6 water ligands

Question 44

What are the colours of the metal aqua ions?

Answer 44

[Cu(H2O)6]2+ blue [Fe(H2O)6]2+ green [Fe(H2O)6]3+ pale violet [Al(H2O)6]3+ colourless

Question 45

What is a hydrolysis reaction?

Answer 45

Where molecules are split apart by water so metal aqua ions lose one or more H2O ligands

Question 46

Why are [M(H2O)4(OH)2] and [M(H2O)3(OH)3] complexes insoluble in water?

Answer 46

Neutral complexes so form as precipitates

Question 47

Why are solutions of aqueous metal ions often acidic?

Answer 47

Metal aqua ions lose H+ from one or more water ligands so H+ makes solution acidic The higher the charge on metal in metal aqua ion the more acidic the solution as electrons in the covalent bond are pulled more strongly a way from H and towards O breaking O-H bond

Question 48

How do the metal aqua ions react with NaOH?

Answer 48

[Fe(H2O)6]2+ + 2OH- —> [Fe(H2O)4(OH)2] + 2H2O (green ppt) [Cu(H2O)6]2+ + 2OH- —> [Cu(H2O)4(OH)2] + 2H2O (blue ppt) [Fe(H2O)6]3+ + 3OH- —> [Fe(H2O)3(OH)3] + 3H2O (brown ppt) [Al(H2O)6]3+ + 3OH- —> [Al(H2O)3(OH)3] + 3H2O (white ppt) WITH XS OH-: [Al(H2O)3(OH)3] + OH- —> [Al(H2O)2(OH)4] + H2O (white ppt dissolves)

Question 49

How do metal aqua ions react with NH3?

Answer 49

[Fe(H2O)6]2+ + 2NH3 —> [Fe(H2O)4(OH)2] + 2NH4+ (green ppt) [Cu(H2O)6]2+ + 2NH3 —> [Cu(H2O)4(OH)2] + 2NH4+ (blue ppt) WITH XS: [Cu(H2O)4(OH)2] + 4NH3 —> [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH- (deep blue solution) [Fe(H2O)6]3+ + 3NH3 —> [Fe(H2O)3(OH)3] + 3NH4+ (brown ppt) [Al(H2O)6]3+ + 3NH3 —> [Al(H2O)3(OH)3] + 3NH4+ (white ppt)

Question 50

How do metal aqua ions react with Na2CO3?

Answer 50

[Fe(H2O)6]2+ + CO3 2- —> FeCO3 + 6H2O (green ppt) [Cu(H2O)6]2+ + CO3 2- —> CuCO3 + 6H2O (blue-green ppt) 2[Fe(H2O)6]3+ + 3CO3 2- —> 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2 (brown ppt with gentle bubbles CO2) 2[Al(H2O)6]3+ + 3CO3 2- —> 2[Al(H2O)3(OH)3] + 3H2O + 3CO2 (white ppt with gentle bubbles of CO2)