For idometric titration of copper, why is HCl added to KIO3 and then titrated immediatedly?
What would happen if iodine-thiosulfate titration was done in a highly acidic solution?
If the copper reaction solution was basic, how would the iodine-thiosulfate reaction be influenced?
a)Oxygen can oxidize iodide to I2 so you want to minimize that possibility (more I2 causes more thiosulfate to be used and results for Cu are high).
b) I don't know if this refers to the titration itself or if it refers to the Cu determination. If the Cu, you want it buffered between about 4.5 and 5.5 or so.
c) To basic and the hydroxide ppts
a)Oxygen can oxidize iodide to I2 so you want to minimize that possibility (more I2 causes more thiosulfate to be used and results for Cu are high).
b) I don't know if this refers to the titration itself or if it refers to the Cu determination. If the Cu, you want it buffered between about 4.5 and 5.5 or so.
c) Too basic and the hydroxide ppts
In the idometric titration of copper, HCl is added to KIO3 and titrated immediately for a specific reason.
Firstly, KIO3 acts as a source of iodate ions (IO3-) in the presence of acid. When HCl is added to KIO3, it reacts with it to form iodine (I2) and chlorine gas (Cl2). The reaction can be represented as follows:
HCl + KIO3 -> I2 + Cl2 + KCl + H2O
The iodine (I2) produced in this reaction is then immediately titrated with a thiosulfate solution (usually sodium thiosulfate, Na2S2O3). The thiosulfate ions (S2O3^2-) react with iodine according to the following balanced equation:
I2 + 2S2O3^2- -> 2I^- + S4O6^2-
The reaction between iodine and thiosulfate is a redox reaction, where iodine gets reduced to iodide (I^-) while thiosulfate gets oxidized to tetrathionate (S4O6^2-).
Now, let's address your second and third questions:
If the iodine-thiosulfate titration was done in a highly acidic solution, it would have an impact on the reaction. In a highly acidic solution, the acid would react with thiosulfate ions, leading to the formation of sulfur dioxide (SO2), rather than iodine being reduced to iodide. This would result in erroneous titration results, as the reaction would not proceed as expected.
In the case of a basic solution for the copper reaction, the iodine-thiosulfate reaction would be influenced differently. A basic solution contains hydroxide ions (OH-) that could react with iodine to form iodate ions (IO3-). This reaction consumes iodine, reducing the amount available for titration. As a result, the titration would underestimate the amount of iodine present, leading to inaccurate results.
In summary, it is important to add HCl to KIO3 and titrate immediately in idometric titration of copper to ensure that the iodine generated is titrated before any interfering reactions occur. Additionally, maintaining the appropriate acidic conditions and avoiding highly acidic or basic solutions in the iodine-thiosulfate titration is crucial to obtain accurate results.