352 GROUP VII: THE HALOGENS
(a) (i) What is the general chemical formula of the hydrides?
(ii) What is the type of chemical bonding encountered in the
pure hydrides?
(b) Refer to the data in the above table and explain briefly
(i) the increase in melting point of the hydrides along the
series chlorine, bromine and iodine,
(ii) the relatively high melting point of the hydride of fluorine.
(c) Give balanced ionic equations describing the reaction(s)
between concentrated sulphuric acid and
(i) solid sodium chloride,
(ii) solid sodium iodide.
(L,A)- Comment on the following:
(a) The electron affinities of fluorine and chlorine are — 333 and
— 364kJmol"^1 respectively; but their standard electrode
potentials are H-2.87 and -f 1.36V respectively.
(b) Iodine forms some electropositive compounds.
(c) In dilute aqueous solution hydrogen fluoride is a weak acid
but the acid strength increases with the concentration of
hydrogen fluoride.
(d) Elements exhibit their highest oxidation state when combined
with fluorine.
(e) NaF is slightly alkaline in aqueous solution.