A solution of I 2 in aqueous KI on reaction with an aqueous solution of N a 2 S 2 O 3 gets decolourised. The reaction taking place here is

Question

A solution of I 2 in aqueous KI on reaction with an aqueous solution of N a 2 S 2 O 3 gets decolourised. The reaction taking place here is, N a 2 S 2 O 3 + H 2 O + I 2 → N a 2 S 2 O 4 + 2 H I, 2 N a 2 S 2 O 3 + I 2 → N a 2 S 4 O 6 + 2 N a I, N a 2 S 2 O 3 + 2 H 2 O + 2 I 2 → N a 2 S 2 O 5 + 4 H I, N a 2 S 2 O 3 + 2 H 2 O + 2 I 2 → N a 2 S 4 O 8 + 4 H I

MARKS App · Accepted Answer

On running sodium thiosulphate solution into an iodine solution (in KI solution), the reddish-brown colour is gradually discharged through yellow to colourless. I 2 + 2 e - → 2 I - 2 N a 2 S 2 O 3 → N a 2 S 4 O 6 + 2 N a + + 2 e - 2 N a 2 S 2 O 3 + I 2 → N a 2 S 4 O 6 + 2 N a + I -

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