Dtermine the strength og given unknown cuso4 solution by titrating against hypo solution
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Theory: The strength of sodium thiosulphate (hypo) solution is determined by
iodometric method (Note 1). When KI is added to the solution of cupper sulphate, an
equivalent amount of I2 is liberated along with the formation white precipitate (of
cuprous iodide, Cu2I2). This free iodine (I2), which remains in solution as [KI3] complex
(Note 2) is then titrated with sodium thiosulphate solution using starch as indicator (Note
3). At the end point of the titration, the blue colour (due to formation of starch – iodine
complex) of solution will disappear and a white precipitate of the Cu2I2 will remain in
conical.
The reactions that are taking place are:
2CuSO4 + 4KI I2 + Cu2I2 + 2K2SO4 ----------[1]
[KI + I2 KI3,] ----------[2]
2Na2S2O3 + I2 Na2S4O6 + 2NaI ----------[3]
(oxidation state of S2 : +4 oxidation state of S2 in sodium tetrathionet : +5)
Procedure: Burette was rinsed and filled up to the zero mark with hypo solution. 10ml of
supplied known strength cupper sulphate solution was pipetted out in a clean conical
flask. 5ml of 5% KI solution was added in that conical flask and mixed well (Note 4).
hope it will help you...
iodometric method (Note 1). When KI is added to the solution of cupper sulphate, an
equivalent amount of I2 is liberated along with the formation white precipitate (of
cuprous iodide, Cu2I2). This free iodine (I2), which remains in solution as [KI3] complex
(Note 2) is then titrated with sodium thiosulphate solution using starch as indicator (Note
3). At the end point of the titration, the blue colour (due to formation of starch – iodine
complex) of solution will disappear and a white precipitate of the Cu2I2 will remain in
conical.
The reactions that are taking place are:
2CuSO4 + 4KI I2 + Cu2I2 + 2K2SO4 ----------[1]
[KI + I2 KI3,] ----------[2]
2Na2S2O3 + I2 Na2S4O6 + 2NaI ----------[3]
(oxidation state of S2 : +4 oxidation state of S2 in sodium tetrathionet : +5)
Procedure: Burette was rinsed and filled up to the zero mark with hypo solution. 10ml of
supplied known strength cupper sulphate solution was pipetted out in a clean conical
flask. 5ml of 5% KI solution was added in that conical flask and mixed well (Note 4).
hope it will help you...
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