Transition Metals

Question 1

Define transition metal

Answer 1

A transition metal is one that forms at least one stable ion with a partially filled d subshell.

Question 2

Which two elements are part of the d block but not considered transition metals?

Answer 2

Zinc and Scandium

Question 3

Give the charge, electron configuration and reason as to why Scandium is not a transition metal.

Answer 3

Sc3+
[Ar] 4s0 3d0
Sc3+ is the only ion. The d subshell is empty.

Question 4

Give the charge, electron configuration and reason as to why Zinc is not a transition metal.

Answer 4

Zn2+
[Ar] 4s0 3d10
Zn2+ is the only ion. The d subshell is full.

Question 5

What are the two exceptions when writing electron configuration of transition metals?

Answer 5

Chromium (4s1 3d10)
Copper (4s1 3d10)

Question 6

How are electrons lost from a transition metal?

Answer 6

First in, first out. So 4s are lost before 3d

Question 7

4 features of transition metals

Answer 7

1. Form complex ions
2. Coloured ions
3. Catalytic properties
4. Variable oxidation states

Question 8

Define coordinate bond.

Answer 8

A covalent bond is formed when both electrons are donated from the same atom.

Question 9

Define ligand

Answer 9

A molecule/ion with a lone pair can form a coordinate bond with a metal ion.

Question 10

Define coordination number

Answer 10

Number of coordinate bonds with the central metal ion

Question 11

Define complex ion

Answer 11

Central metal ion surrounded by ligands

Question 12

Monodentate ligand

Answer 12

Each ligand forms one coordinate bond

Question 13

Bidentate ligand

Answer 13

Each ligand forms 2 coordinate bonds

Question 14

Examples of monodentate ligands

Answer 14

H2O-:
Cl-:
:-NH3
:-CN

Question 15

Examples of bidentate ligands

Answer 15

Ethane-1,2-diamine, or 1,2-diaminoethane (NH2CH2CH2NH2)
Ethanedioate ion (C2O4 2-)

Question 16

Common shapes which transition metal complexes form

Answer 16

Octahedral
Square planar
Tetrahedral
Linear

Question 17

What shape do complexes forming 6 coordinate bonds occupy? Give an example

Answer 17

Octahedral
Copper (II) Hexa Aqua Ion ([Cu(H2O)6]2+)

Question 18

What shapes do complexes forming 4 coordinate bonds occupy? Give examples

Answer 18

1. Tetrahedral
   Cobalt (II) Chloride Ion ([CoCl4]2-)
2. Square Planar
   Nickel (II) Tetra Cyano Ion ([Ni(CN)4]2-)

Question 19

What shape do complexes forming 2 coordinate bonds occupy? Give an example and its use.

Answer 19

Linear
Silver (I) Ammonia Ion ([Ag(NH3)2]+)
The active part of Tollens’ reagent used to distinguish between aldehydes and ketones

Question 20

Example of a hexadentate ligand

Answer 20

EDTA 4-
Occupies octahedral shape
Two coordinate bonds from N atoms and four coordinate bonds from the O- ions

Question 21

Why do chloro complexes tend to be tetrahedral?

Answer 21

The chloride ligand is too big to fit any more than 4 Cl- ligands around the metal ion

Question 22

Show how the complex [Cu(H2O)6]2+ can be converted into [Cu(H2O)2(NH3)4]2+ and state the colour of the new complex

Answer 22

[Cu(H2O)6]2+ + 4NH3 <—-> [Cu(H2O)2(NH3)4]2+ + 4H2O
DEEP BLUE

Question 23

When does the chelate effect occur?

Answer 23

When a monodentate ligand is substituted by a bidentate or multidentate ligand

Question 24

An example of the chelate effect
[Cu(H2O)6]2+ + 3H2NCH2CH2NH2 <–> [Cu(H2NCH2CH2NH2)3]2+ + 6H2O

Answer 24

6 monodentate H2O ligands are replaced by 3 bidentate ethane-1,2-diamine ligands.
4 molecules on left turn into 7 molecules on right
Large increase in entropy
Thermodynamically very favourab;e
Entropy (ΔS) is positive.

Question 25

EXAM STYLE QUESTION: Explain why this reaction is feasible: [Cu(NH3)6]2+ + 3H2NCH2CH2NH2 <--> [Cu(H2NCH2CH2NH2)3]2+ + 6NH3

Answer 25

- Enthalpy change approximately zero = same number of Cu-N bonds broken and formed - Large increase in entropy, positive entropy = 7 molecules produced from 4 molecules - Therefore, ΔG= negative

Question 26

Bonding in haemoglobin

Answer 26

Made of central Fe2+ ion, forms 4 bonds to ring system called porphyrin. - Bond in square planar arrangement- 4 coordinate bonds between Fe2+ and N atoms in haem structure. - 1 coordinate bond between Fe2+ and globin protein. - 1 coordinate bond between Fe2+ and O2 molecules.

Question 27

What happens when O2 molecule has been transported around the body to where it is needed?

Answer 27

Coordinate bond breaks releasing O2 CO2 can bond in its place to be transported to lungs

Question 28

Why is CO toxic?

Answer 28

CO is toxic because CO bonds more strongly to the Fe2+ in haemoglobin. This prevents O2 from bonding to the Fe2+, causing suffocation.

Question 29

Steroisomer definition

Answer 29

Have same structural formula but different arrangement of atoms in space.

Question 30

Two types of stereoisomerism

Answer 30

Geometrical isomerism- Cis-trans isomerism Optical isomerism- non-superimposable mirror images

Question 31

Example of octahedral complex with cis-trans isomerism

Answer 31

[CoCl2(NH3)4]+

Question 32

Example of square planar complex with cis-trans isomerism

Answer 32

[PtCl2(NH3)2]

Question 33

What is the cis isomer of [PtCl2(NH3)2] known as and what is it effective for?

Answer 33

Known as cisplatin Effective anti-cancer drug

Question 34

How does cisplatin work to prevent DNA replication?

Answer 34

Cisplatin binds to DNA in cancer cells and stops cell replication. The 2 Cl- ions on Cisplatin are substituted for 2 N atoms on adjacent guanine bases.

Question 35

Example of cis-trans isomerism with bidentate ligand

Answer 35

[Cr(H2O)2(C2O4)2]-

Question 36

When does optical isomerism occur in complexes?

Answer 36

Complexes form with at least 2 bidentate ligands and 2 monodentate ligands Structure has to be cis.

Question 37

What is optical isomerism

Answer 37

A form of stereoisomerism where the complex forms non-superimposable mirror images of itself.

Question 38

What is the only method of finding which isomer is present?

Answer 38

Using the fact that optical isomers rotate a plane of polarised light in opposite directions.

Question 39

Examples of optical isomer complexes

Answer 39

[Ni(H2NCH2CH2NH2)3]2+ [Co(H2O)2(C2O4)2)

Question 40

Why are transition metals coloured?

Answer 40

All have partially filled d subshells All d orbitals are of equal energy= ground state Presence of other atoms causes d orbitals to have change in energy Enables e- to be excited from one d orbital to another. Energy needed for transition taken from visible light Colour of light absorbed missing from the light that reflects from substance. Colour seen is reflected/transmitted. Diff in energy between d subshells= ΔE

Question 41

ROY

Answer 41

Low energy

Question 42

BIV

Answer 42

High energy

Question 43

If a transition metal has small ΔE...

Answer 43

- Low energy light (ROY) absorbed to excite e- - BIV reflected - Compound looks blue/purple

Question 44

If a transition metal has a big ΔE...

Answer 44

- High energy light (BIV) absorbed to excite e- - ROY reflected - Compound looks red/orange

Question 45

What changes alter the colour of a compound

Answer 45

Change in LIGANDS Change in OXIDATION STATE of metal Change in COORDINATION NUMBER of complex Change in SHAPE of complex

Question 46

Method to find concentration of unknown sample from callibration curve

Answer 46

1. Measure the absorbance of known concentrations 2. Plot graph of absorbance v. concentration 3. Read value of concentration from measured absorbance of unknown from graph.

Question 47

Catalyst definition

Answer 47

Substance that increases ROR without being used up itself

Question 48

How do catalysts work

Answer 48

Decrease activation energy by providing alternative pathway

Question 49

Heterogenous catalyst definition

Answer 49

Catalyst is in different phase to reactants

Question 50

Homogeneous catalyst definition

Answer 50

Catalyst is in same phase as reactants

Question 51

Heterogeneous catalyst process

Answer 51

1. Reactants ADSORB onto surface of catalyst on an active site. 2. Reaction occurs on surface of catalyst. 3. Products desorb from surface of catalyst.

Question 52

How to make catalyst efficient

Answer 52

Increase SA Spread catalyst over inert support medium

Question 53

What happens when catalyst poisoning occurs?

Answer 53

Impurities can block active sites Prevents reactants from adsorbing Purifying reactants is the best way to prevent poisoning.

Question 54

Examples of heterogeneous catalysts

Answer 54

1. Making ammonia in Haber process CATALYSED BY IRON N2 + 3H2 <--> 2NH3 2. Making sulfuric acid in Contact process CATALYSED BY SOLID VANADIUM OXIDE (V2O5) SO2+ V2O5 <--> SO3 + V2O4 2V2O4 + O2 <--> 2V2O5 overall: 2SO2 + O2 <--> 2SO3 3. Manufacture of methanol first forms synthesis gas: CH4 + H2O --> CO + 3H2 then reaction catalysed by solid chromium oxide Cr2O3: CO + 2H2 --> CH3OH

Question 55

Example of homogeneous catalyst

Answer 55

Peroxodisulfate ions oxidise iodide ions to iodine.

Question 56

Why does uncatalysed reaction of peroxodisulfate ions// ethanedioic acid have high activation energy?

Answer 56

Uncatalyzed has high activation energy because 2 negative ions repel.

Question 57

Equations for example of homogeneous catalyst

Answer 57

Uncatalysed: S2O8 2- + 2I- --> 2SO4 2- + I2 Catalysed by Fe2+: 1. S2O8 2- + 2Fe 2+ --> 2SO4 2- + 2Fe 3+ 2. 2I- + 2Fe 3+ --> I2 + 2Fe 2+

Question 58

Autocatalyst definition

Answer 58

One product of reaction catalysed reaction as it proceeds further.

Question 59

Example of autocatalyst

Answer 59

Oxidation of ethanedioic acid by manganate ions

Question 60

Equations for example of autocatalyst

Answer 60

Uncatalysed: 2MnO4 - + 16H+ + 5C2O4 2- --> 2Mn2+ + 8H2O + 10CO2 Catalysed: 1. 4Mn2+ + MnO4- + 8H+ --> 5Mn3+ + 4H2O 2. 2Mn3+ + C2O42- --> 2CO2 + 2Mn2+ Purple to clearer

Question 61

Conc v time graph for this reaction

Answer 61

1. Rate starts slow- no catalyst initially 2. Two negatively charged reactants collide with a very high Ea 3. Then some Mn2+ is formed, rate increases and reaction is being increasingly catalysed. 4. Rate decreased and levels off at reactants used up.