Inorganic II - Transition metals

Question 1

What are transition metals?

Answer 1

Elements in the d-block of the periodic table with a partially-filled d orbital.

Question 2

What are the special chemical properties of transition metals?

Answer 2

• Form complexes
• Form coloured ions
• Have variable oxidation states
• Good catalysts

Question 3

What is a ligand?

Answer 3

A molecule or ion that forms a co-ordinate bond with a transition metal donating a pair of electrons.

Question 4

Name some common ligands.

Answer 4

Cl-
H2O
NH3

Question 5

What is a complex?

Answer 5

A central atom or ion surrounded by ligands.

Question 6

What is the co-ordination number?

Answer 6

The number of co-ordinate to the central atom or ion.

Question 7

What is the equation of the ligand substitution of [Co(H2O)6]2+ with NH3?

Answer 7

[Co(H2O)6]2+ + 6NH3 → [Co(NH3)6]2+ + 6H2O

Question 8

What is the equation of the ligand substitution of [Cu(H2O)6]2+ with Cl-?

Answer 8

[Cu(H2O)6]2+ + 4Cl- → [CuCl4]2- + 6H20

Question 9

What are bidentate ligands?

Answer 9

Ligands able to form two coordinate bonds as they have two electron pairs.

Question 10

Name two bidentate ligands.

Answer 10

Ethanedioate ions ( a lone pair on two of the oxygens)
Ethane-1,2- diamine ( a lone pair on each of the nitrogen atoms)

Question 11

What are multidentate ligands?

Answer 11

Ligands able to form up to 6 coordinate bonds.

Question 12

Name 2 multidentate ligands.

Answer 12

EDTA4-
Heam

Question 13

What is the equation of the ligand substitution of [Fe(H2O)6]3+ and EDTA4-?

Answer 13

[Fe(H2O)6]3+ + EDTA4- → [FeEDTA]-1 + 6H2O

Question 14

How is oxygen transported in the blood?

Answer 14

Oxygen forms a co-ordinate bond to Fe (II) in heamoglobin, allowing it to be transported around the blood.

Question 15

Why is carbon monoxide toxic to humans?

Answer 15

It replaces the oxygen in the heam complex, preventing it from being transported around the body.

Question 16

What is the chelate effect?

Answer 16

Bidentate and multidentate ligands replace unidentate ligands to form complexes. The enthalpy change is very small as the bonds being formed are similar to the bonds being broken. Entropy increases when bi and multidentate ligands are added, making the free energy change more negative, making the reaction more feasible.

Question 17

Which complexes are octahedral?

Answer 17

Complexes with H2O and NH3 ligands form octahedral complexes with a bond angle of 90 degrees.

Question 18

How does cis-trans isomerism occur in complexes?

Answer 18

This type of isomerism is shown by octahedral complexes with different types of ligands. Ligands of the same type can either be next to (cis) or opposite each other (trans).

Question 19

How does optical isomerism occur in complexes?

Answer 19

This type of isomerism is shown by octahedral complexes with bidentate ligands. The isomers are mirror images.

Question 20

Which complexes are tetrahedral?

Answer 20

Larger ligands such as Cl- form tetrahedral complexes with a bond angle of 109.5 degrees. These can also show optical isomerism.

Question 21

Which complexes are square planar?

Answer 21

Platinum and nickel complexes form in a square planar shape with 90 degree bond angles.

Question 22

Which complexes are linear?

Answer 22

Silver complexes are linear with 180 degree bond angles.

Question 23

Which complex is present in Tollen’s reagent?

Answer 23

[Ag(NH3)2]+

Question 24

What is a use of cisplatin?

Answer 24

This is the cis isomer of a square planar complex of platinum with Cl- and NH3 ligands. It is used as an anti cancer drug.

Question 25

What determines the colour of a transition metal?

Answer 25

Coordination number, type ligand and oxidation state.

Question 26

Why are transition metal ions coloured?

Answer 26

Electrons in the d-orbital become excited when hit by light, reflecting some wavelengths and absorbing other, leading to coloured ions.

Question 27

What is the colour and ion formula of vanadium when it has an oxidation state of +5?

Answer 27

(VO2)+, yellow

Question 28

What is the colour and ion formula of vanadium when it has an oxidation state of +4?

Answer 28

(VO)2+, blue

Question 29

What is the colour and ion formula of vanadium when it has an oxidation state of +3?

Answer 29

V3+, green

Question 30

What is the colour and ion formula of vanadium when it has an oxidation state of +2?

Answer 30

V2+, violet

Question 31

What is an equation of the reduction of vanadium under acidic conditions?

Answer 31

Ions are reduced under acidic conditions 2(VO2)+ + 2e- + 4H+ → 2(VO)2+ + 2H2O

Question 32

What is an equation of the oxidation of vanadium under alkaline conditions?

Answer 32

(VO)2+ + H2O → (VO2)+ + 2H+ + e-

Question 33

What is the equation for the reaction between tollen's reagent and an aldehyde?

Answer 33

RCHO + 2[Ag(NH3)2]+ + 3OH- → RCOO- + 2Ag + 4NH3 + 2H2O

Question 34

What is the half equation for the reduction of MnO4-?

Answer 34

MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

Question 35

What is the half equation for the oxidation of Fe2+?

Answer 35

Fe2+ → Fe3+ + e-

Question 36

What is the half equation for the oxidation of (C2O4)2-?

Answer 36

(C2O4)2- → 2CO2 + 2e-

Question 37

What is a catalyst?

Answer 37

A substance that speeds up rate of reaction by providing an alternative reaction pathway without being used up.

Question 38

What is a heterogenous catalyst?

Answer 38

A catalyst that is in a different phase or state to the species in the reaction.

Question 39

Give an example of a heterogenous catalyst.

Answer 39

A solid iron catalyst is used to speed up the reaction between hydrogen and nitrogen gases in the Haber process.

Question 40

Why are transition metals good catalysts?

Answer 40

They have variable oxidation states. Electrons are transferred to produce a reactive intermediate and speed up the reaction rate.

Question 41

What is the Contact process?

Answer 41

The conversion of sulphur dioxide to sulphur trioxide with a vanadium oxide catalyst.

Question 42

What is the equation of the overall reaction of the contact process?

Answer 42

2SO2 + O2 → 2SO3

Question 43

What is the equation of the action of the catalyst in the contact process?

Answer 43

V2O5 + SO2 → V2O4 + SO3 V2O4 + 1/2O2 → V2O5

Question 44

How does adsorption work?

Answer 44

Molecules are adsorbed onto the active site on the surface of the catalyst. These active sites increase the proximity of molecules and weaken the covalent bonds in the molecules.

Question 45

What does the strength of adsorption depend on?

Answer 45

The type of catalyst

Question 46

Which transition metals make the best catalysts?

Answer 46

Iron, cobalt and nickel as they are relatively cheapand increase the rate of reaction the most.

Question 47

What is catalyst poisoning?

Answer 47

Heterogenous catalysts can be poisoned with impurities which block active site and prevent adsorption. Therefore the catalyst has no effect on the rate of reaction.

Question 48

What is an example of catalyst poisoning?

Answer 48

Sulphur impurities poison the solid iron catalyst used in the Haber process.

Question 49

What is a homogenous catalyst?

Answer 49

A catalyst in the same phase as the species in the reaction.

Question 50

What is the overall reaction between S2O8- ions and I- ions?

Answer 50

S2O8- + 2I- → I2 + 2(SO4)2-

Question 51

What are the intermediate reactions between S2O8- and I- ions?

Answer 51

S2O82- + 2Fe2+ →2Fe3+ + 2(SO4)2- 2Fe3+ + 2I- → 2Fe2+ + I2

Question 52

How do homogenous catalysts work?

Answer 52

By combining with the reactants to produce a reactive intermediate. This changes the reaction pathway to one with a lower activation energy, making the reaction more feasible.

Question 53

What is autocatalysis?

Answer 53

A reaction where one of the products can act as a catalyst. This means as the product increases, the rate of reaction also increases.

Question 54

What is an example of autocatalysis?

Answer 54

The redox reaction between MNO4- ions and C2O42- ions in acidic conditions.

Question 55

What is the overall equation of the redox reaction between MNO4- and C2O42- ions?

Answer 55

2MNO4- + 16H+ + 5C2O42- → 2Mn2+ + 8H2O + 10CO2

Question 56

What are the intermediate reactions between MNO4- and C2O42-?

Answer 56

4Mn2+ + MnO4- + 8H+ → 5Mn3+ + 4H2O 2Mn3+ + C2O42- → 2CO2 + 2Mn2+