GROUP VII: THE HALOGENS 351
is then recrystallised from 50 % nitric acid. The iodic acid is then
heated at a temperature maintained between 500 K and 550 K in
order to dehydrate it to iodine pentoxide.(a) Indicate which elements change in oxidation number during
this set of reactions, and the changes involved.
(b) Why is it necessary to perform the oxidation of iodine in a
fume cupboard?
(c) State one observation which would tell you the oxidation of
iodine is complete.
(d) Iodine vapourises readily. Explain how loss of iodine from the
reaction mixture is prevented in this experiment.
(e) Describe briefly how you would recrystallise iodic acid from
50% nitric acid.
(f) How would you heat iodic acid in such a way as to maintain
its temperature between 500 K and 550 K?
(N,A)- By considering the trends in the vertical groups of the Periodic
Table, deduce possible answers to the following questions con-
cerning the element astatine (At), atomic number 85.
(a) State, giving an equation, how astatine could be prepared
from an aqueous solution of potassium astatide K+At~~.
(b) State what you expect to observe when concentrated sulphuric
acid is added to solid potassium astatide.
(c) Name an insoluble astatide, and write its formula.
(d) State, giving a reason, whether ethyl astatide would be more
or less reactive than ethyl chloride, when heated with a
nucleophilic reagent.
(e) The isotope is^0 At is formed by the emission of one jS- particle
from an unstable nucleus. Give the mass number and the
number of neutrons in this parent element.
(f) State two reasons why you are unlikely to perform (or see
performed) experiments involving astatine.
(JMB, A)- The following table shows the atomic numbers of the elements
in Group VII of the Period Table and the melting points of their
hydrides.
Fluorine Chlorine Bromine IodineAtomic number 9 17 35 53
Melting point of hydride (K) 210 178 205 236