2.5 Transition Metals

Question 1

What are the properties of transition metals?

Answer 1

complex formation,
formation of coloured ions,
variable oxidation state
catalytic activity.

Question 2

Name 2 examples of bidentate ligands.

Answer 2

NH2CH2CH2NH2 and ethanedioate ion C2O4 2-

Question 3

Name one example of a multidentate ligand and how many co ordinate bonds can it form?

Answer 3

EDTA4- can form 6 co ordinate bonds.

Question 4

What is the equation links the colour and frequency of the light absorbed with the energy difference between the split d orbitals.

Answer 4

ΔE = hv.
v = frequency of light absorbed (unit s-1 or Hz) 
h= Planck’s constant 6.63 × 10–34 (J s)
DeltaE = energy difference between split orbitals (J)

Question 5

What is the method for spectrophotometry?

Answer 5

Add an appropriate ligand to intensify colour
Make up solutions of known concentration
Measure absorption or transmission
Plot graph of absorption vs concentration
Measure absorption of unknown and compare

Question 6

What are the 4 oxidation states and colours of vanadium?

Answer 6

VO2+ Oxidation state +5 ( a yellow solution)
VO2+ Oxidation state + 4 (a blue solution)
V3+ Oxidation state + 3 (a green solution)
V2+ Oxidation state + 2 (a violet solution)

Question 7

What is the redox equation for the manganate titration with Fe and what is the colour change you observe?

Answer 7

MnO4-(aq) + 8H+ (aq) + 5Fe2+ (aq) —> Mn2+ (aq) + 4H2O (l) + 5Fe3+ (aq)

Purple —> colourless

Question 8

What acid is used to provide H+ ions in the magnate titration?

Answer 8

Dilute sulphuric acid

Question 9

Write both steps and the overall equation for the contact process.
Is this heterogeneous or homogeneous?

Answer 9

Overall equation : 2SO2 + O2 —> 2SO3
step1: SO2 +V2O5 —> SO3 + V2O4
step 2: 2V2O4 + O2 —> 2V2O5
Heterogeneous

Question 10

What reaction does Cr2O3 catalyse?

Is this heterogenous or homogenous?

Answer 10

Cr2O3 catalyst is used in the manufacture of methanol from carbon monoxide and hydrogen. CO + 2H2 —> CH3OH
Heterogenous

Question 11

What are the steps and overall reaction between iodide and persulfate ions

Answer 11

S2O82- + 2I- —> 2SO42- + I2

stage 1 S2O82- + 2Fe2+ —> 2SO42- +2Fe3+
stage2 2I- + 2Fe3+ —> 2Fe2+ + I2

Question 12

Write the steps and overall equations for the reactions between manganate and ethandioate ions.
Is this heterogeneous or homogenous?

Answer 12

2 MnO4- + 5 C2O42- + 16 H+ —> 2Mn2+ + 10 CO2 + 8 H2O
Step 1 4Mn2+ + MnO4- + 8 H+ —> 5Mn3+ + 4 H2O
Step 2 2Mn3+ + C2O42- —> 2Mn2+ + 2 CO2
Homogenous