23 Tranistion Metals

Question 1

Definition of transition metal element

Answer 1

The formal definition of a transition element is that it is one that forms at least one stable ion with a path full d-shell of electrons. Scandium only forms Sc3+ (3d0) and zinc only forms Zn2+ (3d10). ( they are d block elements but not transition metals)

Question 2

Chemical properties of transition metals

Answer 2

Variable oxidation states - have more than one oxidation state
Colour - different coloured ions
Catalysis - affects the rate of reaction without being used up
Complex formation - transition elements form complex ions

Question 3

Co-ordination number

Answer 3

The number of ligand molecules bonded to a metal ion

Question 4

Ligand

Answer 4

An atom, ion or molecule that forms a co-ordinate (dative) bond with a transition metal ion using a lone pair of electrons

Question 5

Example of ligands

Answer 5

H2O:
:NH3
:Cl-
:CN-

Question 6

Aqua ions

Answer 6

If you dissolve the salt of a transition metal in water

Copper sulphate = the positive charged metal ions becomes surrounded by water molecules acting as ligands

Question 7

Multidentate ligands

Answer 7

More than one atom with a lone pair of electrons which can bond to a transition metal ion

Question 8

Bidentate ligands

Answer 8

Ethane 1,2 diamine

Ethanedioate (oxalate) ion

Benzene -1,2- diol

Question 9

Chelate effect

Answer 9

Add a hexadentate ligand such as EDTA to a solution of a transition metal salt

[Cu(H2O)6]2+ + EDTA4- —— [CuEDTA]2- +6H2O

Question 10

Haemoglobin

Answer 10

Red pigment in blood
Responsible for carrying oxygen from the lungs to the cells of the body
Fe2+

Question 11

Tranistion metals

Answer 11

Electrons are being added to the d-sub-level
Good conductor of heat and electricity
Hard , strong ,high melting and boiling point
Low chemical reactivity

Question 12

co-ordination number

Answer 12

number of co-ordinate bonds to ligands that surround the d-block metal ion

Question 13

Aquas ions

Answer 13

dissolve the salt of a transition metal in water, the positively charged metal ion becomes surrounded by water molecules acting as ligands

Question 14

Ethane-1,2-diamine

Answer 14

each nitrogen had a lone pair which can forms a co-ordinate bond to the metal ion

Question 15

EDTA

Answer 15

this can act as a hexadentate ligand using Loeb pairs on four oxygen and both nitrogen atoms. complex ions with polydentate ligands are called chelates. Chelates can be used to effectively removed d-block metal ions from solution

Question 16

chelate effect

Answer 16

enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating ligands for the same metal.

Question 17

Haemoglobin

Answer 17

red pigment
carries oxygen form the lungs
four of the co-ordination sites are taken up by a ring system called a porphyrin which acts as a tetra dentate ligand.

Question 18

anaemia

Answer 18

shortage of haemoglobin

body suffers from a lack of oxygen

Question 19

metal compounds are coloured

Answer 19

coloured is caused by the compounds absorbing energy that corresponds to light in the visible region of the spectrum.

Question 20

why are transition metal complexes coloured

Answer 20

transition metal compounds are coloured because they have part filled d-orbitals
electrons can move between d-orbitals

Question 21

E = hv = hc/λ

Answer 21

frequency of light is related to the energy difference
frequency is related to the colour of light. violent is of high energy and therefore high frequency and red is low energy and low frequency

colour of transition metal complex depends on the energy gap which depends on the oxidation number and also on the ligands.

Question 22

Colorimetry

Answer 22

a simple colorimeter uses a light source and a sector to measure the amount of light of a particular wavelength that passes through a coloured solution. the more concentrated the solution, the less light transmitted through the solution. a colorimeter is used with a suitable calibration graph to measure the concentration of solutions of coloured transition metal compounds.

Question 23

redox titrations

Answer 23

find out how much acid is required to react with certain volume of base
Fe2+ reacts with potassium manganate int he ratio 5:1
using a burette, you gradually add potassium manganate solution to solution containing Fe2+ ions acidified with excess dilute sulphuric acid. the purple colour disappers as the MnO4- ions are converted to pale pink Mn2+ ions to leave a virtually colourless solution.

Question 24

oxidation of transition metal ions in alkaline solutions

Answer 24

high oxidation state of a mental are reduced in acidic solution. oxidation of lower oxidation states of transition metal ions tends to happen in alkaline solution

Question 25

catalyst

Answer 25

affect the rate of reaction without being chemically changed themselves

Question 26

heterogenous catalyst

Answer 26

heterogenous catalysts are present in a reaction in a difference phase than the reactants.
catalytic action occurs on the solid surface
reactants pass over the catalyst surface, which remains in place so the catalyst is not lost and does not need to be separated from the products.
(A heterogeneous catalyst is in a different phase from the reactants and the reaction occurs at active sites on the surface)

Question 27

making heterogenous catalyst more efficient

Answer 27

increase their surface area

spread the catalyst onto an inert support medium. this increases the surface-to-mass ratio, so a little goes a long way.

Question 28

catalysts don’t fast forever

Answer 28

overtime surfaces become covered with unwanted impurities. ( poisoning).
catalyst converters become poisoned by substances used in fuel additive
finely divided catalyst may gradually be lost from the support medium

Question 29

Haber process

Answer 29

iron catalyst

last around 5 years before it become poisoned by impurities in the gas stream

Question 30

contact process

Answer 30

produces sulphuric acid

2SO2 + O2 <====> 2SO3

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

vanadium oxide is regenerated unchanged. each of the two steps has a lower activation energy than the uncatalysed single step

Question 31

manufacture of methanol

Answer 31

synthesis gas is made from methane
CH4(g) + H2O(g) —> CO + 3H2(g)
CO + 2H2(g) —> CH3OH(g)

reaction is catalysed by chromium oxide

Question 32

homogeneous catalyst

Answer 32

when the catalyst is in the same phase as the reactant, an intermediate species is formed.

Question 33

autocatalysis

Answer 33

when one of the products of the reaction is the catalyst. so the reaction starts slow and as the concatenation increase the rate of reaction

Question 34

oxidation of ethanediol acid by manganate ions

Answer 34

example of an auto catalysed reaction
titration
2MnO4-(aq) + 16H+ 5C2O42-(aq) —–> 2Mn2+(aq) + 8H2O(l) + 10CO2(g)

4Mn2+(aq) + MnO4- (aq) + 8H+(aq) —> 5Mn3+(aq) + 4H2O(l)
2Mn3+(aq) + C2O42-(aq) –> 2CO2(g) + MN2+(aq)

reaction is followed using a colorimeter to measure the concentration of MnO4- which is purple

Question 35

complex

Answer 35

central metal atom or ion surrounded by ligands.

Question 36

monodentate

Answer 36

H2O, NH3 and Cl−

Question 37

what two ligands are similar in size?

Answer 37

NH3 and H2O

Question 38

Haem

Answer 38

In haemoglobin

Haem is an iron(II) complex with a multidentate ligand.

Question 39

carbon monoxide and haemoglobin

Answer 39

Oxygen forms a co-ordinate bond to Fe(II) in haemoglobin, enabling oxygen to be transported in the blood.
Carbon monoxide is toxic because it replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin.

Question 40

Tollens’ reagent

Answer 40

Ag+ forms the linear complex [Ag(NH3)2]+ as used in Tollens’ reagent

Question 41

Vanadium and oxidation states

Answer 41

Vanadium species in oxidation states IV, III and II are formed by the reduction of vanadate(V) ions by zinc in acidic solution.