4. The disproportionation reactions of chlorine and chlorate(I). Disproportionation is the name for a reaction where an element simultaneously oxidises and reduces. Chlorine with water: Cl2 (aq) + H2O(l) HClO(aq) + HCl (aq) Chlorine is both simultaneously reducing and oxidising If some universal indicator is added to the solution it will first turn red due to the acidity of both reaction products. It will then turn colourless as the HClO bleaches the colour. Reaction with water in sunlight If the chlorine is bubble through water in the presence of bright sunlight a different reaction occurs 2Cl2 + 2H2O 4H+ + 4Cl- + O2 The same reaction occurs to the equilibrium mixture of chlorine water. The greenish colour of chlorine water fades as the Cl2 reacts and a colourless gas (O2 ) is produced Chlorine is used in water treatment to kill bacteria. It has been used to treat drinking water and the water in swimming pools. The benefits to health of water treatment by chlorine outweigh its toxic effects. Reaction of Chlorine with cold dilute NaOH solution: Cl2 ,(and Br2 , I2 ) in aqueous solutions will react with cold sodium hydroxide. The colour of the halogen solution will fade to colourless Cl2 (aq) + 2NaOH(aq) NaCl (aq) + NaClO (aq) + H2O(l) The mixture of NaCl and NaClO is used as Bleach and to disinfect/ kill bacteria The greenish colour of these solutions is due to the Cl2 Naming chlorates/sulphates In IUPAC convention the various forms of sulfur and chlorine compounds where oxygen is combined are all called sulfates and chlorates with relevant oxidation number given in roman numerals. If asked to name these compounds remember to add the oxidation number. NaClO: sodium chlorate(I) NaClO3 : sodium chlorate(V) K2SO4 potassium sulfate(VI) K2SO3 potassium sulfate(IV)
188.8.131.52 Uses of chlorine and chlorate(I)
The reaction of chlorine with water to form chloride ions and chlorate(I) ions.
The reaction of chlorine with water to form chloride ions and oxygen.
Appreciate that society assesses the advantages anddisadvantages when deciding if chemicals should be added to water supplies.
The use of chlorine in water treatment.
Appreciate that the benefits to health of water treatment by chlorine outweigh its toxic effects.
The reaction of chlorine with cold, dilute, aqueous NaOH and uses of the solution formed.