Modern inorganic chemistry

350 GROUP VII: THE HALOGENS

Table 11.4

PRELIMINARY TESTS FOR HALIDE IONS

Test

Warm
concentrated
H 2 SO 4 on
the dry solid

Silver nitrate
solution

Chlorine water
(acidified
NaCIO solution)

Calcium nitrate
solution

F"

HF

evolved

No ppt.

No

action

White

ppt.

cr

HCl

evolved

White ppt..

soluble in

dil. ammonia

solution

No

action

No ppt.

Br~

HBr, SO 2

and Br 2

evolved

Cream ppt.,

soluble in

cone, ammonia

solution

Br 2 liberated

No ppt.

r

S0 2 , H 2 S.

and I 2

evolved

Yellow ppt..

almost

insoluble in

cone, ammonia

solution

I 2 liberated

No ppt.

QUESTIONS

1. Give a comparative account of the oxo-acids of the halogens
   from the viewpoint of:

(a) their acid properties or the thermal stability of their alkali

salts,

(b) their properties as oxidants, (L, S)

2. lodic acid may be made by oxidising iodine with excess fuming
   nitric acid according to the equation

I 2 + 10HNO 3 -> 2HIO 3 + 10NO 2 + 4H 2 O

The iodic acid may then be dehydrated by heat, giving iodine
pentoxide
2HIO 3 -> I 2 O 5 + H 2 O

The practical details are as follows:

About 0.5 g of iodine is placed in a small flask fitted with a long
reflux air condenser and 15cm^3 of fuming nitric acid (b.p. 380 K)
are added. The mixture is then heated on a water bath at 385-390 K
in a fume cupboard until the reaction seems to be complete. This
takes about an hour. The solution is then transferred to an evapora-
ting basin and evaporated to dryness on a steam bath. The iodic acid