7.5.2 Transition Metals
Questions
Section A
Section B
1.
The
chlorate(I) ion (hypochlorate)
liberates oxygen when warmed with a cobalt(II) salt which acts as a catalyst.
(a)
(i) Write an equation for the decomposition of
the chlorate(I) ion.
[2]
(ii)
Using
the concept of oxidation states explain how the cobalt(II) salt catalyses the
decomposition.
[4]
(b)
Transition
metals can act as heterogeneous catalysts in hydrogenation reactions.
(i)
Explain the term heterogeneous as applied to a catalysed reaction.
[2]
(ii)
Write
an equation for an hydrogenation reaction.
[2]
(iii)
Which
transition element is normally used in hydrogenation reactions?
[1]
(c)
Platinum
and rhodium, which are also transition elements, are used in the catalytic
converters in vehicles.
(i)
Into
what products are the following converted when passed through the catalytic
converter?
carbon monoxide
hydrocarbons
nitrogen oxides
[3]
(ii)
Explain
why leaded petrol should not be used in cars fitted with a catalytic converter.
[2]
2. (a) Vanadium exists in several oxidation states, some of which are coloured. Complete the following table.
|
Oxidation state |
Formula |
Colour |
|
+5 |
VO2+ |
yellow |
|
+4 |
VO2+ |
|
|
+3 |
V3+ |
|
|
+2 |
V2+ |
violet |
(b) The table below shows the redox potentials of these vanadium ions and other species.
Eo /V
Mg2+
(aq) +
2e- Mg
(s) -2.37
Zn2+
(aq) +
2e- Zn
(s) -0.76
Fe2+
(aq) +
2e- Fe
(s) -0.44
V3+
(aq) +
e- V2+ (s) -0.26
VO2+
(aq) +
2H+ (aq) + e- V3+ (aq) + H2O (l) +0.34
Fe3+
(aq) + e- Fe2+ (aq) +0.77
VO2+
(aq) +
2H+ (aq) + e- VO2+ (aq) + H2O (l) +1.00
(i) Which species in the table is the strongest reducing agent ?
[1]
(ii) Predict what would be observed when the following mixtures are prepared. Write an equation for any reaction taking place.
A solution containing V2+ (aq) is mixed with acidified solution containing VO2+ (aq).
[2]
A piece of zinc was dipped into a solution containing V3+ (aq).
[2]
(c) If solutions of vanadium(III) chloride, VCl3, and potassium cyanide, KCN, in water are mixed and alcohol is added a complex cyanide, K3V(CN)6, is precipitated.
(i) The cyanide ion acts as a ligand. Explain the term ligand.
[2]
(ii) Suggest the coordination number of vanadium in the complex. Explain your answer.
[2]
(iii) Explain the formation of the complex from the aqueous vanadium ion in terms of ligand replacement.
[3]