Solutions in different beakers change their colors from colorless to orange and then become dark-blue one by one
name: Clock reaction between bisulfite, iodate and mercury(II) ions gives orange mercury iodide precipitate and after this - the dark-blue complex of iodine and starch
Mercury compounds are highly toxic! Filter off the mercury(II) iodide precipitate. If some of the mercury(II) chloride solution was unused, add excess sodium hydroxide to precipitate mercury hydroxide. Filter off the mercury hydroxide precipitate.
All mercury compounds should be placed in sealed containers for professional disposal .
Wear eye protection and lab gloves.
Always follow general safety
recommendations. Please note that conducting chemistry
experiments you must comply with the relevant legal procedures in
Firstly the iodate(V) ions oxidize the hydrogensulphite ions:
IO3- + 3HSO3- → I2 + 3SO42- + 3H+
The hardly soluble mercury iodide is formed from Hg2+ and I-.
As soon as concentration of the HgI2 exceed its solubility, the solid orange mercury(II) iodide precipitates.
After all mercury ions form a precipitate, excess of the I- ions stays.
There is a reaction of comproportionation between the iodide and the iodate ions in the formed solution. Molecular iodine is formed.
Then dark-blue complex I2 and starch is formed.