ACIDS AND BASES: OXIDATION AND REDUCTION 109
Identify the oxidising agent and the reducing agent in each
reaction and write 'half-equations' showing the donation or
acceptance of electrons by each of these eight reagents.
(C,S)Discuss (a) the acidity and (b) the substitution reactions of
metal hexa-aquo cations, [M(H 2 O) 6 ]?I^ (where n — 2 or 3),
giving two examples of each type of reaction. Discuss the effect
upon the stabilities of the -f 2 and + 3 oxidation states of
(i) increasing the pH in iron chemistry, and
(ii) complex formation (with ligands other than water) in
cobalt chemistry.
(JMB, A)Liquid ammonia, which boils at 240 K, is an ionising solvent.
Salts are less ionised in liquid ammonia than they are in water
but, owing to the lower viscosity, the movement of ions
through liquid ammonia is much more rapid for a given
potential gradient. The ionisation of liquid ammoniais very slight. The ionic product [NH^NH^T] = 10~^28
mol^2 dm"^6 at the boiling point. Definitions of an acid and a
base similar to those used for aqueous solvents can be used for
solutes in liquid ammonia. This question is mainly about
acid-base reactions in liquid ammonia as solvent.(a) Write the formula of the solvated proton in the ammonia
system.
(b) In the ammonia system state, what are the bases correspond
ing to each of the following species in the water system?
(c) Write equations for the reactions in liquid ammonia of :
(i) sodium to give a base and hydrogen,
(ii) the neutralisation reaction corresponding to :
HCl(aq) -f NaOH(aq) -* NaCl(aq) + H 2 O(1)
(d) What would the concentration be of NH^T (in mol dm"^3 )
in a solution of liquid ammonia containing 0.01 mol dm"^3
of ammonium ions?
(e) The dissociation constant of ethanoic (acetic) acid in liquid
ammonia is greater than it is in water. Suggest a reason for
the difference.
(N.A)