17/18 Transition metals/aqueous ions

Question 1

transition metal

Answer 1

form one or more stable ions with an incomplete d sub-shell (an incomplete d sub-level in atoms or ions)

Question 2

ligand

Answer 2

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

Question 3

complex

Answer 3

a central metal atom or ion surrounded by coordinately bonded ligands.

Question 3

characteristic properties

Answer 3

characteristic properties
* complex formation
* formation of coloured ions
* variable oxidation state
* catalytic activity.

Question 4

co-ordination number

Answer 4

number of co-ordinate bonds to the central metal atom or ion

Question 5

Monodentate ligands

Answer 5

H2O, NH3 and Cl−
can act as monodentate ligands.

Question 6

When Coordination number changes

Answer 6

Size of ligand
eg water or ammonia replaces by chloride is from 6 to 4.

Question 7

Bidentate ligands

Answer 7

H2NCH2CH2NH2 and C2O4
2–

ethanediamine
ethanedioate

Question 8

Chelation/ Chelate effect.

Answer 8

Bidentate and multidentate ligands replace monodentate ligands from complexes.

Question 8

Multidentate ligands

Answer 8

EDTA4–

Question 9

Why is CO toxic.

Answer 9

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

Replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin.

Question 10

What causes a colour change?

Answer 10

Change in:
Coordination number
Ligand
Oxidation state

Question 11

Example of a tetrahedral complex:

Answer 11

copper tetrachloride

(tetrachloride)
109.5 degrees

Question 11

Example of an octahedral complex:

Answer 11

Hexa aqua iron 2 (hexaaqua/hexaamine)
90 degrees
can display cis trans with monodentate ligands
and optical isomerism with bidentate ligands.

Question 12

Example of a linear complex:

Answer 12

Ammonical silver nitrate
Ag TM
2 ammonia
180 degrees
used in tollens

Question 12

Example of a square planar complex:

Answer 12

Cis/transplatin
Pt TM
2 ammonia 2 chloride
90 degrees

Question 13

What is the eqn for ∆E

Answer 13

∆E = hν = hc/λ
E = energy,
h = Planck’s constant,
ν = frequency,
c = the speed of light,
λ = wavelength

Question 13

Why/How do TM change colour?

Answer 13

Certain wavelengths of light are absorbed exciting d electrons from ground to excited state (∆E), the remaining range of wavelengths are reflected and correspond to a certain colour.

Different ligands, coord number, oxidation state or Ph alter ∆E and change colour.

Question 14

Why are 3+ ions more acidic than 2+

Answer 14

Act as a lewis acid, have a higher charge density.

Polarises the water molecule

Weakens OH bond in water

releasing H+ ions (deprotonates)

Question 15

Why do most ligand substitution reactions have a ∆H close to zero?

Answer 15

Coordination number stays the same

Atoms that coordinately bond to TM are relatively similar in size

OR

6 of the same bond broken and remade just from a different ligand such as water and ethanedioate.

Slight differences may be due to differences in electronegativity. (O to N - O harder to overcome bond so endothermic)

Question 16

Reaction of hexaaqua iron (2)/(3) and sodium carbonate

Answer 16

(2): produces iron (2) carbonate ppt

(3): CO2 + Fe(H2O)3(OH)3 ppt

Question 17

What catalytic reactions do you need to know?

Answer 17

Contact process: HETERO
Vanadium (V) oxide

Reaction between S2O8 2- and I -: HOMO
Fe 2+

Autocatalysis of MnO4 - and c2o4 2- : HOMO
Mn 2+

Question 17

Why does chelation occur in terms of thermodynamics?

Answer 17

∆G=∆H-T∆S

∆H negligible
make & break same number/type of bonds
OR
Similar Size of atoms that bond to central TM.

increase in entropy
increase in particles in solution

∆G negative (for forward reaction) which is less than zero so feasible.

Question 18

Contact process:

Answer 18

SO2 + 1/2O2 -> SO3

SO2 + V2O5 → SO3 + V2O4

1/2 O2 + V2O4 → V2O5

Question 19

Reaction between S2O8 2- and I -

Answer 19

S2O8 2- + 2I- —-> 2SO4 2- + I2

2Fe2+ + S2O8 2- →2Fe3+ +2SO4 2-

2Fe3+ + 2I- → 2Fe2+ + I2

Question 20

reaction between
C2O4
2– and MnO4 -

Answer 20

2MnO4 − + 16H+ + 5C2O4 2− → 2Mn2+ + 8H2O + 10CO2

4Mn2+ + MnO4 − + 8H+ → 5Mn3+ + 4H2O

2Mn3+ + C2O4 2− → 2Mn2+ + 2CO2

Question 21

Why are catalysts required in TM reactions?

Answer 21

2 neg ions repulsion

changes oxidation states

ions have alternative route

Question 22

Heterogeneous catalysts: meaning, action

Answer 22

In a different phase/state (from the reactants)

Provides sites for adsorption.
Reactants bind to active sites
Bonds weaken/reaction takes place
Products desorb

Question 23

Catalytic poisoning: what is it and how to prevent

Answer 23

Poison/contaminants attach to surface
Prevents access to active sites

Purify reactants

Question 24

How to maximise efficiency of heterogenous catalysts:

Answer 24

Surface area is increased
by use of powder or granules or finely divided

Question 25

Go to aqueous ions sheet and learn.