4.5K views · 72 reactions | The reactions involved are as follows: Na2S2O5 + H2O → 2 NaHSO3 IO3− + 3 HSO3− → I− + 3 SO42− + 3 H+ This reaction reduces iodate ions to iodide ions. Hg2+ + 2 I− → HgI2 Orange mercury iodide solid is precipitated until the mercury is used up. IO3− + 5 I− + 6 H+ → 3 I2 + 3 H2O The excess I− and IO3− undergo the iodide-iodate reaction I2 + starch → a blue/black complex A blue/black starch-iodine complex is formed. | Chemistry | Facebook