3.2.5 Transition Metals (A2)

Question 1

Where are transition metals found?

Answer 1

In the d-block, in the middle of the periodic table

Question 2

What is a transition metal?

Answer 2

A metal that can form one or more stable ions with a partially filled d-orbital/sub-level

Question 3

What is the electron configuration of Copper and Cu2+?

Answer 3

1) [Ar], 4s1, 3d10

2) [Ar], 3d9

Question 4

What is the electron configuration of Chromium and Cr3+ ion?

Answer 4

1) [Ar], 4s1, 3d5

2) [Ar], 3d3

Question 5

Why isn’t Scandium (Sc) a transition metal?

Answer 5

Only forms one ion, Sc3+, which has an empty d-orbital. Electron configuration is: [Ar], 3d1, 4s2, so when in its ionic form is [Ar].

Question 6

Why isn’t Zinc (Zn) a transition metal?

Answer 6

Zinc only forms one ion, Zn2+, which has a full d-orbital. When Zn2+ loses 2 electrons, both are from the 4s orbital

Question 7

What are the THREE properties that apply to all Transition Metals?

Answer 7

1) All have a High Density
2) All have High Melting and Boiling Points
3) Ionic Radii are more or less the same

Question 8

What special CHEMICAL properties do Transition Metals have?

Answer 8

1) Can form Complex Ions
2) Form Coloured Ions
3) Good Catalysts
4) Can exist in variable oxidation states

Question 9

What is a Complex?

Answer 9

Central Metal atom or Ion surrounded by co-ordinately bonded ligands?

Question 10

What is a co-ordinate (dative covalent bond)?

Answer 10

A covalent bond in which both electrons in the shared pair come from the same atom

Question 11

What is a Ligand?

Answer 11

An atom, ion or molecule that donates a pair of electrons to a central transition metal ion to form a co-ordinate bond

Question 12

What is the co-ordination number?

Answer 12

Number of co-ordinate/dative bonds that are formed with the central metal ion

Question 13

What are the two common co-ordination numbers?

Answer 13

1) 6 (e.g. H2O or NH3)

2) 4 (e.g. Cl-)

Question 14

What shape forms when there are 6 co-ordinate bonds? Give bond angles and example

Answer 14

Octahedral Shape
ALL Bond Angles are 90˚
[Fe(H2O)6]2+

Question 15

What shape forms when there are 4 Co-ordinate bonds? Give bond angles and example

Answer 15

Usually Tetrahedral
109.5˚
Tetrachlorocuprate (II) [Cu(Cl)4]2-
Tetrachlorocobaltate (II) [Co(Cl)4]2-

Question 16

What is the other shape formed when there are 4 Co-ordinate bonds? Give bond angles and example

Answer 16

Square Planar
90˚
Cisplatin (Diamminodichloroplatinum (II), cis-diamminedichloridoplatinum) [Pt(NH3)2(Cl)2]

Question 17

What shape forms when there are 2 Co-ordinate bonds? Give bond angles and example

Answer 17

Linear
180˚
[Ag(NH3)2]+

Question 18

What is the overall charge?

Answer 18

The overall charge one the complex ion is its total oxidation state

Question 19

How do you work out the Oxidation State?

Answer 19

Oxidation State = Total Oxidation State – Sum of oxidation states of the ligands

Question 20

Why must a Ligand have at least one Lone Pair of electrons?

Answer 20

It requires Lone Pairs of electrons to form co-ordinate bonds

Question 21

What are Ligands that only form one co-ordinate bond called?

Answer 21

Monodentate

Question 22

What are Ligands that can form more than one co-ordinate bond called?

Answer 22

Bidentate = 2 Co-ordinate bonds
Multidentate = Multiple Co-ordinate bonds

Question 23

What are the 3 main Bidentate Ligands?

Answer 23

1) Ethane-1,2-diamine. Each has 2 lone pairs and forms 2 co-ordinate bonds with metal ion
2) Ethanedioate. Forms 2 co-ordinate bonds
3) EDTA4- ion. Has 6 lone pairs and forms 6 co-ordinate bonds

Question 24

How is Haemoglobin (Hb) an example of having a Multidentate Ligand?

Answer 24

1) Haemoglobin is protein found in blood that helps transport Oxygen
2) Hb contains Fe2+ which are hexa-coordinated. Six lone pairs are donated to form six co-ordinate bonds in an octahedral structure
3) 4 of the Co-ordinate bonds come from single multidentate Ligand. Four Nitrogen atoms from same molecule co-ordinate around Fe2+ to form a circle. This part is called Haem
4) Other two co-ordinate bonds come from protein called Globin, and either an Oxygen or Water molecule – complex can transport O2 to where its needed, and then swap it for a water molecule
5) Process can be disrupted if Carbon Monoxide is inhaled. Hb swaps Water Ligand for CO ligand, forming Carboxyhaemoglobin. CO is a strong ligand and doesn’t readily exchange with Oxygen or Water Ligands meaning Hb cannot transport O2. CO Poisoning starves organs of Oxygen

Question 25

How can complex ions Show Optical Isomerism?

Answer 25

Complex Ions can show Optical Isomerism (type of Stereoisomerism) – where an ion can exist in two forms that are non-superimposable mirror images.
This happens when three bidentate ligands, such as ethane-1,2-diamine (NH2CH2CH2NH2), co-ordinately bond with a central metal ion, such as Nickel

Question 26

How can Cis-Trans Isomers form Octahedral or Square Planar Complexes?

Answer 26

1) Cis-Trans Isomerism is another form of Stereoisomerism. Its a special case of E/Z Isomerism
2) Octahedral complexes w/4 monodentate ligands of one type and 2 monodentate ligands of another can show Cis-Trans Isomerism. If two odd ligands are opposite then its a Trans isomer. If they’re next to each other its a Cis Isomer
3) Square Planar complex ions that have two pairs of ligands also show Cis-Trans Isomerism. E.g. Cisplatin (an effective Chemotherapy) and Transplatin (Ineffective)

Question 27

How do Ligands split 3d sub-level into two energy levels?

Answer 27

1) When Ligands bond to ions, some of the orbitals gain energy. This splits 3d orbitals into two different energy levels
2) Electrons tend to occupy lower orbitals (ground state). To jump up to higher orbitals (excited states) they need energy equal to the energy gap, ∆E. They get this energy from visible light
3) The energy absorbed when electrons jump up from the ground state to an excited state can be worked out using ∆E = hv = ((hc) ÷ λ)
4) Amount of energy needed to make electrons jump depends on central metal ion and its oxidation state, the ligands and co-ordination #, as these affect size of the energy gap

Question 28

How do you work out the energy when electrons jump to an excited state?

Answer 28

∆E = hv or ∆E = ((hc) ÷ λ)
∆E – Energy Absorbed
h – Planck's Constant (6.63x10(-34) J/s)
v – Frequency of light absorbed (Hertz, Hz)
c – Speed of light (3x10(8) m/s)
λ – Wavelength of light absorbed (m)

Question 29

Why are Transition Metal ions coloured?

Answer 29

1) When visible light hits transition metal ion, some frequencies absorbed when electrons jump to higher orbitals. Frequencies absorbed depend on size of Energy Gap (∆E)
2) Rest of frequencies are transmitted or reflected. Transmitted or reflected frequencies combine to make the complementary colour of the absorbed frequencies – the colour you see
3) e.g. [Cu(H2O)6]2+ ions absorb light from red end of spectrum. Remaining frequencies combine to produce complementary colour – blue
4) If there are no 3d electrons or 3d sub-level is full, the no electrons will jump, so no energy will be absorbed. If no energy is absorbed, compound will look white or colourless

Question 30

How can Spectroscopy be used to Find Concentrations of Transition Metal Ions?

Answer 30

1) White light shone through a filter, which is chosen to only let through complementary colour (colour of light that is absorbed)
2) Light passes through sample to colorimeter, which calculates how much light was absorbed by the sample
3) The more concentrated a solution is, the more light it will absorb. You can use this measurement to work out the concentration of a solution of transition metal ions.

Question 31

What is the term for a ligand being swapped for another?

What does it usually cause?

Answer 31

1) Ligand Substitution or Exchange

2) A colour change

Question 32

What happens if the ligands being substituted are of similar size and have the same charge?

Answer 32

Co-ordination number doesn’t change and neither does the shape

Question 33

What happens if the ligands being substituted are different sizes?

Answer 33

There is a change of Co-ordination number and change of shape

Question 34

Can Ligand Substitution Reactions be reversed?

Answer 34

Ligand substitution reaction can be reversed easily, UNLESS the new complex ion is more stable than the old one

Question 35

How does a Positive Entropy Change make a more Stable complex?

Answer 35

1) When ligand exchange reaction occurs, dative bonds broken and formed. Strength of those broken often v. similar to those being formed. So enthalpy change is usually v. small. e.g. Ethane-1,2-diamine and Nickel
2) Actually reversible, but equilibrium so far to right it is though to be irreversible – [Ni(NH2CH2CH2NH2)3]2+ more stable than [Ni(NH3)6]2+
3) Instead, increase in stability (Chelate Effect), explains why multidentate ligands form more stable complexes than monodentate

Question 36

How can Vanadium (V) ions be reduced?

Answer 36

Add them to Zinc Metal in an Acidic Solution

1) Solution turns from yellow to blue as Vanadium (V) is reduced to Vanadium (IV)
2) Solution then changes from blue to green as Vanadium (IV) becomes (III)
3) Finally, Vanadium (III) is reduced to Vanadium (II), and the solution changes from green to violet

Question 37

How do Redox Potentials tell you how easy it is to reduce an ion?

Answer 37

1) Larger the redox potent., the less stable the ion will be, and more likely to be reduced
3) Redox Potentials are standard electrode potentials, measured with the reactants at a conc. of 1M (mol/dm3) against standard hydrogen electrode under standard conditions
4) Redox Potent. of an ion not always same as its Standard Electrode Potent. It can vary depending on the environment that the ion is in.

Question 38

How does Tollens’ Reagent work?

Answer 38

When added to Aldehydes, Tollens’ oxidises it to a Carboxylic Acid and the Ag+ (Silver) ions are reduced to Silver Metal.
Nothing occurs with Ketones

Question 39

What are Titrations with Transition Element ions known as?

Answer 39

Redox Titrations

Question 40

How do you do a Redox Titration?

Answer 40

1) Measure out quantity of reducing agent (e.g. Aqueous Fe2+ ions) using a pipette, and put it in a conical flask
2) Using a measuring cylinder, add approx. 20cm3 of dilute sulphuric acid to the flask
3) Add Oxidising agent to the reducing agent using a burette
4) Oxidising Agent reacts with reducing agent. Reaction will continue until all of reducing agent is used up. Next drop will give the mixture the colour of oxidising agent
5) Stop when mixture in flask just becomes tainted with colour of oxidising agent (end point) and work out Titre (rough titration)
6) Repeat more accurately, do a few more until 2 or more are within 0.10cm3 of each other

Question 41

What is the main oxidising agent that is used?
What does it contain?
What conditions are required for ions to be reduced?

Answer 41

1) Aqueous Potassium Manganate (VII)
2) It contains PURPLE Manganate (VII) ions.
3) Strong Acidic Conditions

Question 42

How do you use Titration Results to work out Concentration of Reagent?
e.g. 27.5cm3 of 0.02M Manganate (VII) reacted with 25cm3 of Acidified Sodium Ethanedioate solution. Work out conc. of (C2O4)2- ions in solution

Answer 42

1) Work out # of moles of (MnO4)- added to flask = (Conc x vol) ÷ 1000 = (0.02x27.5) ÷ 1000 = 5.5x10(-4)
2) Look at balanced equation to work out # of mol of C2O4 react with every mol of MnO4 – 5mol of C2O4 react with 2 mol of MnO4. Mol of C2O4 = (5.5x10(-4) x 5) ÷ 2 = 1.38x10(-3) mol
3) Work out # of mol of C2O4 that would be in 1000cm3 (1dm3) of solution (this is concentration) –
25cm3 contained 1.38x10(-3) mol
1000cm3 would contain ((1.38x10(-3)) x 1000) ÷ 25 = 0.552 mol of C2O4.
So conc = 0.552 mol/dm3

Question 43

How do Transition Metal Catalysts Work?

Answer 43

1) By Changing Oxidation State
2) Change Oxidation states by gaining of losing electrons within d orbitals. This means they can transfer electrons to speed up reactions

Question 44

Why are Heterogenous Catalysts in a Different Phase from the Reactants?

Answer 44

1) Heterogeneous Catalyst is one that is in a different phase from reactants (in different physical state), e.g. in Haber Process gases passed over solid iron catalyst
2) Reaction happens on active sites located on surface of heterogeneous catalyst. Increasing SA of catalyst, increasing number of molecules that can react at the same time, increasing rate of reaction
3) Support mediums often used to make area of catalyst as large as possible. Help to minimise cost of reaction, only small coating of catalyst needed to provide large surface area

Question 45

How can Impurities Poison Heterogenous Catalysts?

Answer 45

1) Impurities in reaction mixture can bind to catalyst’s surface and block reactants from being absorbed. This process is called Catalyst Poisoning
2) Catalyst Poisoning reduces Surface Area of Catalyst available to reactants – slowing reaction
3) Poisoning increases cost of chemical process because less product can be made in a certain time or with certain amount of energy. Catalyst may need replacing or regenerating, which cost money

Question 46

What is good about Homogeneous Catalysts?

Answer 46

1) Homogeneous catalysts in same phase as reactants
2) Work by combining reactants to form intermediate species, which then form products and re-form catalyst
3) Enthalpy profile has two humps in it, corresponding to the two steps of reaction
4) Activation Energy needed to form Intermediates lower than needed to make products directly
5) Catalyst always Re-Forms, so it can carry on catalysing reaction

Question 47

What is Autocatalysis?

Answer 47

When Product Catalyses Reaction
e.g. Mn2+
It’s an Autocatalysis reaction because Mn2+ is a product of the reaction it acts as a catalyst for.
Means as reaction progresses and amount of product increases, reaction speeds up

Question 48

What are Metal-Aqua complex ions?

Answer 48

Transition metal compounds dissolved in water. In general, 6 water molecules form co-ordinate bonds with trans metal, e.g. hexa-aqua iron (II) [Fe(H2O)6]2+

Question 49

Why are solutions containing Metal-Aqua Ions Acidic?

Answer 49

1) In solution containing metal-aqua 2+ ions, reaction between metal-aqua ion and the water – hydrolysis
2) Metal-aqua 2+ ions release H+ ions, so acidic solution is formed
3) Only slight dissociation, so solution weakly acidic
4) Metal-aqua 3+ ions react in same way, but dissociate more than 2+ ions, so form more acidic solutions

Question 50

How can you Hydrolyse Metal-Aqua Ions further to form precipitates?

Answer 50

Adding OH- ions to Metal-aqua ions produces insoluble metal hydroxides:

1) In water, metal-aqua 3+ ions form equilibrium. If you add OH- ions, H3O+ ions are removed, shifts equi to right
2) Now another equilibrium is set up in the solution. OH- ions again remove H3O+ ions from solution, pulling equi to right
3) Happens one last time – now left with insoluble uncharged metal hydroxide
4) Same thing happens with Metal-aqua 2+ ions, except only 2 steps instead of 3

Question 51

Why is Aluminium Hydroxide Amphoteric?

Answer 51

When mixed with base, e.g. NaOH, acts as Brønsted-Lowry Acid, donates H+ ions/protons to OH- ions forming soluble compound.
When acid is present, acts as Brønsted-Lowry Base and accepts H+ ions/protons from H3O+ ions in solution