36 . Sulphuric acid : Preparation : By contact process
18 S8 + O2 → SO2
Exothermic reaction and therefore low temperature and high pressure are favourable
SO3 ( g ) + H2 SO4 → H2 S2 O7 ( Oleum )
H2S2O7 + H2O → 2 H2SO4 ( 96 − 98 %)
It is dibasic acid or diprotic acid .
It is a strong dehydrating agent .
It is a moderately strong oxidizing agent .
GROUP 17 ELEMENTS
37 . Atomic and ionic radii : Halogens have the smallest atomic radii in their respective periods because of maximum effective nuclear charge .
38 . Ionisation enthalpy : They have very high ionization enthalpy because of small size as compared to other groups .