2.5 Transition Metals.

Question 1

What is a transition metal?

Answer 1

An element with an incomplete d-sub shell in atoms or ions. Ti → Cu

Question 2

Why is zinc not a transition metal?

Answer 2

Zn only forms a 2+ ion which has a complete d- subshell.

Question 3

4 characteristics of transition metals

Answer 3

• Complex formation.
• formation of coloured ions
• variable oxidation states
• catalytic activity

Question 4

What is a complex?

Answer 4

A central metal ion surrounded by ligands.

Question 5

What is a ligand?

Answer 5

An atom, ion or molecule which can donate a lone election pair

Question 6

What is a coordinate bond?

Answer 6

A covalent bond in which both electrons in the shared pair come from the same atom or ion.

Question 7

What is mono dentate/ multidentate/ Bidentate

Answer 7

Monodentate= only forming one coordinate bond per ligand
Multidentate = forming more than 2 coordinate bonds.
Bidentate = forming 2 coordinate bonds.

Question 8

What is the coordination number

Answer 8

Number of coordinate bonds from ligands to metal ion

Question 9

what are Lewis acid/bases?

Answer 9

Lewis acid= lone pair acceptor (metal)
Lewis base = lone pair donor (Ion)

Question 10

rules of electron configuration of the transition metals

Answer 10

4s orbital fills before 3d
4s empties before 3d (in ions)

Question 11

exceptions for the rules of electron configuration of transition metals

Answer 11

in chromium and copper, the 3d is filled first to provide more stability.
e.g. Cr - [Ar] 3d5 4s1, Cu - [Ar] 3d10 4s1

Question 12

4 examples of common monodentate ligands

Answer 12

H2O, NH3, Cl- and CN-

Question 13

2 examples of common bidentate ligands

Answer 13

1,2-diaminoethane (en)
ethanedioate (C2O4^21)

Question 14

example of a common multidentate ligand and how many co-ordinate bonds does it form

Answer 14

EDTA^4-, forms 6 co-ordinate bonds

Question 15

structure of haemoglobin

Answer 15

a globular protein with 4 Fe2+ centres, with a ligand taking up 4 co-ordinate sites, oxygen takes one site and haem takes the other.

Question 16

what is cis-trans isomerism and when can it occur

Answer 16

occurs in square planar and octahedral complexes
cis = when the same ligands are next to eachother.
trans = when the same ligands are opposite eachother.

Question 17

4 possible shapes of complexes + bond angles

Answer 17

linear, 180
square planar, 90
tetrahedral, 109.5
octahedral, 90

Question 17

what is optical isomerism and when can it occur

Answer 17

occurs in octahedral complexes
when complexes have the mirror image to eachother

Question 18

what is d orbital splitting

Answer 18

when a ligand causes the 5 d-orbitals to split into 3 and 2 orbitals - one set higher than the other- the difference in energy cause a high energy d-orbital and a low energy d-orbital.

Question 19

how can electrons transfer between high/low energy d-orbitals

Answer 19

when electrons absorb light, they become excited and are promoted to a higher energy level

Question 20

how do you work out the difference in energy between the high and low energy d-oritals

Answer 20

ΔE (J) = hv = hc/λ
h = plancks constant
v = frequency of light absorbed
c = velocity of light
λ = wavelength of light

Question 21

what does ΔE depend on

Answer 21

1. the metal ion
2. the ligand
3. the oxidation state
4. the co-ordination number

Question 22

how does visible colour arise

Answer 22

visible light is a mixture of colours that are not absorbed

Question 23

what is UV/visible spectrometry and how does it work

Answer 23

a way to measure the frequency at which complexes absorb UV/visible light.
UV/visible light is passed through the complex, light which pass through are detected and those that do not, are not.

Question 24

what is colorimetry

Answer 24

a way to measure concentration of solutions

Question 25

steps of colorimetry

Answer 25

a calibration series of solutions with known concentrations is prepared. a colorimeter is used to measure absorption. a calibration curve is plotted. a sample with an unknown concentration is measured in the calorimeter. the absorbance is matched to the calibration curve.

Question 26

why can transition metals have variable oxidation states

Answer 26

the energy of the different d orbital are similar, so they metal will still be stable with varied oxidation states

Question 27

reduction of vanadium

Answer 27

vanadium is reduced by the presence of zinc in acidic solution. vanadium is reduced from VO2 + -> VO2+ -> V3+ -> V2+. the oxidation state going from +5 -> +2. colour goes from yellow -> blue -> green -> violet

Question 28

what is a redox titration

Answer 28

a titration to find out the concentration of oxidising or reducing agents

Question 29

role of potassium manganate

Answer 29

contains MnO4- which is a common oxidising agent. dilute sulfuric acid needs to be present in the conical flask. potassium manganate is in the biuret and will be added until the end point, a purple solution.

Question 30

what is a homogeneous and heterogeneous catalyst

Answer 30

homogeneous catalyst: catalyst in the same phase as the reactants heterogeneous catalyst: catalyst in a different to the reactants

Question 31

heterogenous catalysts

Answer 31

usually solids, occur with gaseous or aqueous reactants. the reaction will occur on the surface of the catalyst. e.g. the haber process, the contact process

Question 32

homogeneous catalysts

Answer 32

an intermediate species is formed, and the reaction requires a lower activation energy. e.g. the reaction between iodide and persulfate ions

Question 33

what is catalyst poisoning

Answer 33

when impurities bind to the surface and block active sites of the catalysts, reducing rate of reaction, making the catalyst less efficient.

Question 34

strength of adsorption

Answer 34

the strength of adsorption helps to determine the effectiveness of the catalytic activity. having too strong adsorption means the product isnt released but having a weak adsorption means the product isnt adsorbed in a high enough concentration

Question 35

why is the reaction between iodide and persulfate ions very slow

Answer 35

they are both negative ions, so there is a strong repulsion power which needs to be overcome in order to collide.

Question 36

what is autocatalysis

Answer 36

when the product is the catalyst. as the reaction continues and more product is made, rate of reaction will increase. e.g. reaction between ethanedioate and manganate ions