All the halogens combine with hydrogen to form hydrogen halides
(HX).
(i) Preparation of HF and HCl : These are prepared by heating fluorides and chlorides respectively with conc.
H2SO4.
Heat
CaF2 + H2SO4 ————> CaSO4 + 2HF
Heat
2NaCl + H2SO4 ————> Na2SO4 + 2HCl
(ii) Preparation of HBr and HI :These are prepared by heating bromides and iodides respectively with phosphoric acid
Heat
3NaBr + H3PO4 ————> Na3PO4 + 3HBr
Heat
3NaI + H3PO4 ————> Na3O4 + 3HI
Conc.
H2SO4 cannot be used for the preparation of
and
because these being strong reducing agents reduced
H2SO4 to SO2 and are themselves oxidised to Br2
and I2
respectively.
2HBr +
H2SO4 ———> SO2
+ Br2 + 2H4O |
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