The elements of Group 7, the halogens, have many important uses. Fluorine is used to make sulfur hexafluoride, $$\(\mathrm{SF}_{6}\)$$, a gas which is used as an insulator in electrical equipment. Chlorine is used as a bleach and as a disinfectant in water treatment. Bromine is used to make organic chemicals that are used as fire retardants. lodine has been used in the catalyst in the manufacture of ethanoic acid. （b）Bleach， $$\(\mathrm{NaClO}(\mathrm{aq})\)$$ ，is formed by the reaction of chlorine with cold，dilute aqueous sodium hydroxide． Equilibrium $$\(1 \quad \mathrm{HClO}(\mathrm{aq}) \rightleftharpoons \mathrm{H}^{+}(\mathrm{aq})+\mathrm{ClO}^{-}(\mathrm{aq})\)$$ VAY甘 SIHI NI BIYM ION OO $$\[ \mathrm{Cl}_{2}(\mathrm{~g})+2 \mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{NaClO}(\mathrm{aq})+\mathrm{NaCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \]$$ The following species and equilibria are present in solutions of $$\(\mathrm{NaClO}(\mathrm{aq})\)$$ ． Equilibrium $$\(2 \quad \mathrm{HClO}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})+\mathrm{H}^{+}(\mathrm{aq}) \rightleftharpoons \mathrm{Cl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})\)$$ Equilibrium $$\(3 \quad \mathrm{Cl}_{2}(\mathrm{aq}) \rightleftharpoons \mathrm{Cl}_{2}(\mathrm{~g})\)$$ Household bleach is stored at a pH between 11 and 13. Household bleach should not be stored near strong acid． （i）Give the formula of the chlorine－containing species present at highest concentration in household bleach at pH 12. （1） ................................................................................................................................................................................................................................................................................ （ii）Explain why mixing strong acid with bleach is dangerous． YZ4Y SUH NI AIIM IONOO Justify your answer using the equilibria shown． （3） VB4甘 SIHI NI BH\＆M ION OO (iii) On heating, NaClO disproportionates to form sodium chloride and sodium chlorate(V). Give the equation for this disproportionation reaction. State symbols are not required. (2)

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