Chapter 24 Transition Elements

Question 1

What are the D block elements?

Answer 1

Elements found between group 2 and group (1)3
Highest energy electron found in a d orbital

Question 2

What are the electron configurations of chromium and copper?

Answer 2

Cr= …3d5 4s1
Cu= 3d10 4s1

Half or full d sub shell more stable than not, and so electron excites from the 4s orbtial

Question 3

Which orbital for d block elements is removed first?

Answer 3

4s
It’s why a lot of d block elements have 2+ ions
Filling 4s first, also empties first as the energy of the 3d falls below that of the 4s when both are filled

Question 4

What is the definition for transition metals? What D block elements do not count as transition metals?

Answer 4

D block elements that form at least 1 ion with a partially full d-orbital

Zinc - only Zn2+ so a full d sub shell
Sc- not Sc3+, so an empty d sub shell

Question 5

What are the colours of chromium in various oxidation states?

Answer 5

Cr2+ = light blue
Cr3+ = dark Green
Cr4+ and Cr5+ = colourless
Cr6+ = orange or yellow

Question 6

What is the link between oxidation state and oxidising potential?

Answer 6

Transition metals in high oxidation states are good oxidising agents as the metal complex wants to be reduced
E.g MnO4- +7 wants to be Mn2+

Question 7

What are some examples of transition metals as catalysts?

Answer 7

Haber Process- N2 + 3H2 —/2NH3. Catalysed by Fe
Contact Process- 2SO2 + O2 —/2SO3 Catalysed by V2O5
Iodide-peroxydisulphate- catalyses by Fe2+

Question 8

What is a complex ion?

Answer 8

Central metal ion with one or more ligands bound to it by dative covalent bonds

Question 9

What is a ligand?

Answer 9

A molecule or ion that donates a one pair of electrons to a central metal ion via dative covalent bonding

Question 10

How do you write a complex ion?

Answer 10

Square brackets around the whole complex
Round brackets for the ligands
Charge on the outside

E.g [Cr(NH3)6] 3+

Question 11

What is a coordination number?

Answer 11

The number of dative covalent bonds made to a central metal ion in a complex ion

Question 12

What is the shape of a complex with a coordination number of 6? What about 4?

Answer 12

6-Octahedral
4- usually tetrahedral
But if 8 d electron in the ion, becomes square planar
Usually Pt, Au(III) Pd

Question 13

What is a monodentate ligand? What is a bidentate ligand?

Answer 13

A ligand which is able to donate 1 lone pair of electrons to a central metal ion, forming 1 coordinate bond e.g ammonia

A ligand which is able to donate 2 lone pairs of electrons to a central metal ion via dative covalent bonding e.g ethanedioate

Question 14

When and how is stereoisomerism present in 4 coordinate complexes?

Answer 14

When there no more than 2 identical ligands
Cis/Trans

Same side= Cis, 90 degrees
Opposite side= trans, 180 degrees

Question 15

When does Cis/Trans isomerism occur in 6 coordinate complexes?

Answer 15

When two identical ligands and 2 bidentate ligands
Or 4 identical and 2 different

Same monodentate = 90 degrees, Cis
Opposite monodentate= 180 degrees, Trans

Question 16

Why do some 6 coordinate complexes have optical isomerism and which do?

Answer 16

Mirror images are not superimposable

In Cis 2 bidentate and 2 monodentate
And 3 bidentate

Draw the mirror image

Question 17

What is Cis-platin and how does Cis-platin work?

Answer 17

[Pt(NH3)2Cl2]
Anti-cancer drug which inhibits cell division, shrink tumour sizes but lots of side effects
Forms a complex with guanine where the Cls are substituted by the nitrogen’s in the base, prevents DNA replication and triggers apoptosis

Question 18

What is ligand exchange?

Answer 18

When one ligand is swapped for another

Question 19

What happens when chromium reacts with dropwise then excess ammonia

Answer 19

Originally Cr3+ Violet
Dropwise- base, hydroxide

Cr3+ + 3OH- —/ Cr(OH)3 (s). Grey green

Excess, full substitution

Cr(OH)3 + 6NH3 —/ [Cr(NH3)6]3+ + 3 OH- Purple

Question 20

What happens if chromium hydroxide is reacted with excess NaOH?

Answer 20

Grey-Green to Dark Green
Cr(OH)3 + 3OH- —/ [Cr(OH)6]3-

Question 21

What happens with Cu2+ reacts with dropwise then excess ammonia?

Answer 21

[Cu(H2O)6]2+ pale blue
Dropwise Cu(H2O)6 + 2OH- —/ Cu(OH)2(H2O)4 + 2H2O Blue precipitate
Excess Cu(OH)2(H2O)4 + 4 NH3 —/ [Cu(H2O)2(NH3)4]2+ + 2OH- + 2H2O. Dark Blue solution

Pale blue solution, then blue precipitate, then dark blue solution, partial substitution

Question 22

What happens when Cu2+ reacts with HCl? Why?

Answer 22

[Cu(H2O)6]2+ + 4Cl- —/ [CuCl4]2- + 6H2O

Pale blue to Yellow
Change in coordination number as the chloride ligands are larger than water, physically not enough space for 6 of them

Question 23

Why does adding acid enable transition metal hydroxides to dissolve?

Answer 23

Fe2+ + 2OH- /=/ Fe(OH)2

Reversible reaction, adding acid decreases the concentration of hydroxide
Pushes the position of equilibrium to the left, so more ions less precipitate

Question 24

What is the colour of Fe2+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?

Answer 24

Pale Green solution
Green precipitate
Insoluble

Question 25

What is the colour of Fe3+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?

Answer 25

Pale yellow solution
Orange/brown precipitate
Insoluble

Question 26

What is the colour of Mn2+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?

Answer 26

Pale pink solution
Light brown precipitate
Insoluble

Question 27

What is the structure of Haemoglobin?

Answer 27

Metalloprotein
Fe2+ with a multidentate haem group coordinated to it
1 space of the globulin protein, and the other for oxygen to coordinate to

Question 28

What is the function of Haemoglobin? Why is CO toxic?

Answer 28

To transport oxygen around the body
Coordination of oxygen creates a weak dative covalent bond, this is a reversible reaction and O2 can disassociate where it is needed by cells for respiration
The C of CO forms a much stronger dative covalent bond, substituting for the oxygen, and this is permanent
Oxygen can no longer be transported around the body so cells cannot respire, leading to cell death

Question 29

How do you convert between Fe2+ and Fe3+ including colour changes?

Answer 29

Fe2+= Green Fe3+= orange brown
To produce Fe3+, adding an oxidising agent to Fe2+ such as H+/MnO4-
To produce Fe2+, adding a reducing agent to Fe3+ such as I-

Question 30

How do convert between Cr3+ and Cr2O7 2- including colours and intermediates?

Answer 30

Cr3+=Green Cr2O72-= Orange

Oxidise Cr3+ by reacting with H2O2/OH-, first forming yellow CrO4 2-, then Cr2O7 2-
Reduce Cr2O7 2- with Zn/H+, with excess reducing to form Cr2+ blue

Question 31

What is the reaction between Cu2+ and Iodide?

Answer 31

2Cu2+ + 4I- —/ 2CuI + I2

White solid and brown solution

Question 32

What is the reaction between hot Sulphuric acid and Cu2O?

Answer 32

Cu2O+ H2SO4 —/ Cu + CuSO4 + H2O

Brown solid and blue solution

Question 33

What pH is better for reduction and oxidation?

Answer 33

Reduction= acidic
Oxidation = alkaline

Think about oxidation is the loss of hydrogen and bases remove hydrogens

Question 34

What shape molecules goes silver form as a complex ion?

Answer 34

Linear, only two ligands

Question 35

How do transition metals catalyse reactions when homogeneous?

Answer 35

Relies on the variable oxidation states of transition metal ions
The ion will take the electron from one molecule and reduce itself
It will then oxidise itself by giving the electron to the other reaction
Thus catalysing the reaction and regenerating the catalyst

Needs an electrode potential between the two reactants