Question

why excess of potassium iodide is added in idometry of copper​

Answer 1

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The I2 combines with iodide ion to produce the dark brown triodide ion, I3-. The excess iodide ion also causes the reduced copper to precipitate as white cuprous iodide, CuI. I2 and I3- in solution tend to adsorb on the surface of CuI thus becoming unavailable for rapid reduction by the thiosulfate.

Answer 2

Answer:

The I2 combines with iodide ion to produce the dark brown triodide ion, I3-. The excess iodide ion also causes the reduced copper to precipitate as white cuprous iodide, CuI. I2 and I3- in solution tend to adsorb on the surface of CuI thus becoming unavailable for rapid reduction by the thiosulfate.