Transition Metals

Question 1

What are d block elements

Answer 1

their highest energy electrons are in the d orbital

Question 2

What are transition metals

Answer 2

An element which forms at least one stable ion with a partially full d-shell of electrons

Question 3

What are the characteristics of transition metals

Answer 3

• form complexes
• form coloured ions
• variable oxidation states (they have partially filled d orbitals so can lose 4s and 3d electrons)
• catalytic activity

Question 4

Why is zinc not a transition metal

Answer 4

It can only form a 2+ ion. In this ion the Zn2+ has a complete d orbital

Question 5

What is a complex

Answer 5

A central metal ion surrounded by ligands

Question 6

What is a ligand

Answer 6

An atom, ion or molecule which can donate a lone electron pair to form a dative covalent bond

Question 7

What is the coordination number

Answer 7

The number of dative covalent bonds a ion is forming

Question 8

Explain why complexes formed from transition metal ions are coloured

Answer 8

• some wavelengths of light are absorbed
• to promote electrons in the d orbitals to higher energy levels
• the light that is not absorbed is transmitted to give the substance colour

Question 9

AE = ?

Answer 9

1. plancks constant x frequency of light absorbed
2. plancks constant x speed of light/wavelength of light absorbed

Question 10

Give 3 examples of catalysts and the reactions they catalyse

Answer 10

Iron - Haber process
Vanadium (V) oxide - contact process
MnO2 - decomposition of H2O2

Question 11

Which electrons do transition metals lose first when forming ions

Answer 11

4s

Question 12

How many coordinate bonds does EDTA form

Answer 12

6

Question 13

When a compound is dissolved in water what shape does it form

Answer 13

Octahedral with 6 H20 Ligands

Question 14

Explain the chelate effect in terms of entropy

Answer 14

• multidentate ligands = more molecules
• so significant increase in entropy
• delta G is less than 0
• so reaction is feasible
• more stable complex ion formed

Question 15

What shape is Platin

Answer 15

Square planar - forms Cisplatin

Question 16

How does haemoglobin transport oxygen

Answer 16

Oxygen forms a coordinate bond to Fe(II) in haemoglobin, allowing it to be transported in the blood

Question 17

Why is carbon monoxide toxic

Answer 17

It replaces oxygen coordinately bonded to Fe (II) in haemoglobin

Question 18

What is the chelate effect

Answer 18

Bidendate and multidentate ligands replace monodentate ligands from complexes

Question 19

How would changing a ligand or coordination number change colour

Answer 19

It will alter the energy split between the d orbitals, changing AE and the frequency of light absorbed

Question 20

What can be used to reduce Vanadium

Answer 20

Zinc

Question 21

What colour is MnO4-

Answer 21

Deep purple

Question 22

What colour is Mn2+

Answer 22

Pink

Question 23

What colour is Cr2O7 2-

Answer 23

Orange

Question 24

What colour is Fe2+ aqua ion

Answer 24

Green

Question 25

What colour is Fe3+ aqua ion

Answer 25

Pale brown

Question 26

Why are transition metals good catalysts

Answer 26

They can exist in variable oxidation states so can provide alternative pathways easily

Question 27

What are the 2 equations for vanadium catalyst in the contact process

Answer 27

SO2 + V2O5 —> SO3 + V2O4 2V2O4 + O2 —> 2V2O5

Question 28

Describe how a heterogeneous catalyst works

Answer 28

- the reactants adsorb onto the surface/active sites - the bonds weaken and reaction takes place - the products desorb from the surface

Question 29

Describe how to obtain a calibration graph

Answer 29

- measure absorbance for a range of known concentrations - plot a graph of absorbance vs concentration - read the value of concentration for the measured absorbance from the graph

Question 30

Explain why a compound may be white

Answer 30

- full 3d subshell - so can’t absorb visible light

Question 31

Why might the enthalpy change/AH for a reaction be (almost) 0

Answer 31

Same number and type of bond being broken and made

Question 32

Define autocatalysis

Answer 32

When the product of a reaction is also a catalyst for that reaction

Question 33

Write two equations to show how Fe2+ catalyses the reaction between S2O8(2-) ions and I- ions

Answer 33

S2O8 (2-) + 2Fe2+ —> 2Fe3+ + 2SO4 (2-) 2 Fe3+ +2I- —> 2Fe2+ + I2

Question 34

Define homogenous vs heterogenous catalyst

Answer 34

Homogeneous catalyst is in the same phase as reactants Heterogeneous catalyst is in a different phase from the reactions

Question 35

What is a Lewis acid and base

Answer 35

Acid - electron pair acceptor Base - electron pair donor

Question 36

What colour is V3+

Answer 36

Green

Question 37

What colour is V2+

Answer 37

Violet

Question 38

What colour and oxidation state is VO2 (+)

Answer 38

5+ Yellow

Question 39

What colour and oxidation state is VO (2+)

Answer 39

4+ Blue

Question 40

How could a compound increase the pH

Answer 40

- has a high charge density - so polarise water molecules more - so weakens the OH bond in water, releasing H+ ions

Question 41

What are the monodentate ligands

Answer 41

H20, NH3 and Cl-

Question 42

If CuCl2 solid is dissolved in solution what is its Ligand

Answer 42

[Cu(H20)6] 2+

Question 43

What are the two bidentate ligands

Answer 43

1. Ethane-1,2-diamine NH2CH2CH2NH2 1. Ethanedioate C2O4 (2-) Both form 2 coordinate bonds

Question 44

What is the multidentate ligand called

Answer 44

EDTA (4-) Forms 6 coordinate bonds

Question 45

Explain Cl- effect on the coordination number when it reacts

Answer 45

It decreases eg from 6 to 4 Because Cl- ions are larger so only 4 can fit around the metal ion

Question 46

What is Cis-trans isomerism

Answer 46

Occurs in monodentate Ligands E-Z isomerism Trans - E Cis- Z

Question 47

What type of isomerism occurs in bidentate ligands

Answer 47

Optical isomerism

Question 48

Describe why optical isomerism occurs

Answer 48

The arrangement of the coordinate bonds can lead to enantiomers formed

Question 49

What two factors effect the lifetime of a catalyst

Answer 49

- catalyst poisoning - active sites blocked + large surface area eg by using powder or small pellets

Question 50

Describe a ligand reaction in Gibbs terms in which the no. Of molecules increases

Answer 50

- increase in entropy as more moles of products than reactants - so more disorder - delta S is positive - delta G is negative so reaction is feasible (write equation to work out AG) - delta H is close to 0 because same number and type of of bonds

Question 51

Why might a reaction be slow before a catalyst is added

Answer 51

If there are two negative ions that repel It will make the activation energy higher

Question 52

Why might a ion not be able to catalyse a reaction

Answer 52

- doesn’t have a variable oxidation state

Question 53

Why might two atoms be a good catalyst

Answer 53

Because the two oppositely charged ions attract each other