The acid radicals were separated into three groups according to their behavior towards dil. HCl and Conc. H2SO4.
- Group 1 acid radicals evolving gases with dil. HCl: carbonates (CO32-), bicarbonates (HCO3-), sulphides (S2-), sulphites (SO32-), and thiosulphate (S2O32-).
- Group 2 acid radicals responding to Conc. H2SO4: chlorides (Cl-), bromides (Br-), and iodides (I-).
- Group 3 acid radicals unaffected by both acids: sulphates (SO42-), and phosphates (PO43-).
First, a principle test for the group is carried out to determine which group the acidic radical belongs to. Afterwards, a set of confirmatory tests are carried out to identify the acidic radical.