Group 7: Halogens
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When an aqueous solution of halogen elements is added to an aqueous solution of potassium halides, what would I SEE happen?
Potassium chloride Potassium bromide Potassium iodide
Chlorine no reaction yellow colour (bromine) dark yellow-brown (iodine)
Bromine no reaction no reaction dark yellow-brown (iodine)
Iodine no reaction no reaction no reaction
NB Where there is no reaction, the original colour of the halogen solution will be seen in a diluted state.
Iodine is not soluble in water but it dissolves in the presence of iodide ions. The colour of the solution is the colour of the triiodide ion. The ‘iodine colour’ may appear reddish if the solutions are concentrated. If you add excess chlorine or bromine or to a solution of potassium iodide you will oxidise all the iodide ions and then see greyish crystals of iodine appearing.
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Risk assessment
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updated: 27 August 2003
