reaction between Sodium thio sulfate and Sodium hypochlorite in water

Question

Hi,

If we have a water tank that contains 45000 Liters of water and you add Sodium hypochlorite 12% and the free chlorine in the tank is around 50 ppm, to neutralize we add Sodium thio sulfate to the solution until the free chlorine rate is around 0-0,1 ppm, my question is what is the balanced reaction between these two in the water tank regardless if there are any other contaminates in the water(the reaction between Sodium thio sulfate and Sodium hypochlorite in water)?

thanks in advance

Botan

Answer 1

Sodium thiosulfate is a commonly used quenching agent for sodium hypochlorite. The reaction is ...

4 NaClO + Na₂S₂O₃ + 2 NaOH → 4 NaCl + 2 Na₂SO₄ + H₂O

The thiosulfate (S₂O₃^2-) reduces the hypochlorite (ClO) and becomes sulfate (SO₄^2-), thus essentially removing the hypochlorite. (Note: this takes place under alkaline conditions).

Hope this answers your question.