Oxoacids of chlorine, bromine and iodine

AU hypohalites are unstable with respect to disproportionation (eq. 17.65). At 298 K, the reaction is slow for [OCl] , fast for [OBr] and very fast for [Ol] . Sodium hypochlorite disproportionates in hot aqueous solution (eq. 17.66), and the passage of CI2 through hot aqueous alkali yields chlorate and chloride salts rather than hypochlorites. Hypochlorite solutions decompose by reaction 17.67 in the presence of cobalt(II) compounds as catalysts. 

Like HOCl, chlorous acid, HCIO2, is not isolable but is known in aqueous solution and is prepared by reaction 17.68. It is a relatively weak acid (pX = 2.0). Sodium chlorite (used as a bleach) is made by reaction 17.69. The chlorite ion has the bent structure 17.35. 

In contrast to HOF, HOCl, HOBr and HOI are unknown as isolated compounds, but in aqueous solution they act as weak acids (pX values HOCl, 7.53 HOBr, 8.69 HOI, 10.64). Hypochlorite salts such as NaOCl, KOCl and Ca(OCl)2 (eq. 17.64) can be isolated. NaOCl can be crystallized from a solution obtained by electrolysing aqueous NaCl in such a way that the CI2 liberated at the anode mixes with the NaOH produced at the cathode. Hypochlorites are powerful oxidizing agents and in the presence of alkali convert [IO3] to [IO4], Cr to [Cr04], and 

Alkaline solutions of chlorites persist unchanged over long periods, but in the presence of acid, HCIO2 disproportionates according to eq. 17.70. 

Hypochlorous acid HOCl Chlorous acid HOCIO (HCIO2) 

Oxoacids of chlorine Oxoacids of bromine Oxoacids of iodine  

Hypochlorous acid Chlorous acid HOCl HOCIO (HCIO2) Hypobromous acid HOBr Hypoiodous acid HOI  

Chloric acid HOCIO2 (HCIO3) Bromic acid HOBrOj (HBrOj) Iodic acid HOIO2 (HIO3) 

Perchloric acid HOCIO3 (HCIO4) Perbromic acid HOBrOj (HBr04) Periodic acid Orthoperiodic acid HOIO3 (HIO4) (HO)5lO (HjIOe)  

Chloric and bromic acids, HCIO3 and HBr03, are both strong acids but cannot be isolated as pure compounds. The aqueous acids can be made by reaction 17.71 (compare with reaction 17.68). 

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