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Old Nassau Clock Reaction


  • Solution A: 4gm soluble starch, 15gm NaHSO3 per liter H2O

               Dissolve 4gm soluble starch in 500ml boiling water,
               then add 15gm NaHSO3 and 500ml water.

  • Solution B: 3gm HgCl2 per liter H2O
  • Solution C: 15gm KIO3 per liter H2O



Mix equal amounts of solutions A, B, and C in that order with stirring. Solution turns bright orange, then suddenly turns dark blue.

Or you can pour half of solution C into the mixture and wait until a nice orange color develops before adding the remainder of solution C.



IO< sub="">3- + 3HSO3 --> I- + 3SO42- + 3H+

Hg2+ + 2I- --> HgI2(orange)

6H+ + IO3- + 5I- --> 3I2+ 3H2O

I2 + starch --> (blue)


Waste Management

The used solutions should be collected and given to EH&S as hazardous waste (toxic and corrosive).