excess KI
Iodometric titration involves the titration of iodine with a reducing agent, while iodimetric titration involves the titration of iodide with an oxidizing agent. In iodometric titration, iodine is detected by a starch indicator to determine the end point, while in iodimetric titration, iodide ion concentration is determined by titration with a standard solution of an oxidizing agent.
Adding sulfuric acid before KI in an iodometric titration helps to acidify the solution and prevent the premature oxidation of iodide ions to iodine. This ensures that the iodide ions react with the analyte (substance being tested) instead of being oxidized by any oxidizing agents present in the solution. Acidifying the solution also helps to stabilize the iodine formed during titration.
Some of the metal ion that is estimated (especially Cu2+) may get trapped within starch indicator. When KCNS is added, copper thiocyanate or Cu(CNS)2 complex is formed which then reacts with the KI added, giving correct results.
Potassium iodide (KI) is added in coulometry titration to help facilitate the generation of iodine (I2) following the reduction of iodate ions (IO3-) in the sample solution. The produced iodine can then be titrated with a standardized thiosulfate solution to determine the amount of substance being analyzed. Additionally, KI acts as a stabilizer for iodine, preventing its premature reaction or volatilization.
KI solution is commonly used in idiometric titrations because the presence of iodide ions allows for the detection of certain oxidizing agents through the formation of a characteristic color change with starch indicator. This method is particularly useful for determining the concentration of oxidizing agents such as chlorine or iodine in a sample solution.
Iodometric titration involves the titration of iodine with a reducing agent, while iodimetric titration involves the titration of iodide with an oxidizing agent. In iodometric titration, iodine is detected by a starch indicator to determine the end point, while in iodimetric titration, iodide ion concentration is determined by titration with a standard solution of an oxidizing agent.
In iodometric titrations sodium thiosulfate is the titrant whereas the KI will reduce the analyte; eg: Cu2+ to Cu+. The I2 produced is then titrated by the sodium thiosulphate. Cu2+ + I- --> CuI + I3- I3- + 2 S2O32- ¾® 3 I- + S4O62- To answer your question: KI (reducing agent) is added to generate the iodine by the reduction of the analyte (Cu2+) The formed iodine is then back-titrated with thiosulfate (titrant) to determine the amount of analyte originally present. As you can see the KI and sodium thiosulfate serve two different purposes. KI improves solubility of Iodine
Adding sulfuric acid before KI in an iodometric titration helps to acidify the solution and prevent the premature oxidation of iodide ions to iodine. This ensures that the iodide ions react with the analyte (substance being tested) instead of being oxidized by any oxidizing agents present in the solution. Acidifying the solution also helps to stabilize the iodine formed during titration.
Some of the metal ion that is estimated (especially Cu2+) may get trapped within starch indicator. When KCNS is added, copper thiocyanate or Cu(CNS)2 complex is formed which then reacts with the KI added, giving correct results.
There is no interference with results when already a correct abundancy of both were added. (pH < 5, and more than triple (molar) amount Iodide over the Oxidant)See also: 'Related questions' however.
Potassium iodide (KI) is added in coulometry titration to help facilitate the generation of iodine (I2) following the reduction of iodate ions (IO3-) in the sample solution. The produced iodine can then be titrated with a standardized thiosulfate solution to determine the amount of substance being analyzed. Additionally, KI acts as a stabilizer for iodine, preventing its premature reaction or volatilization.
Acetic acid is added in the titration reaction to provide the acidic conditions necessary for the reaction between KI and N-bromosuccinimide to occur effectively. The acidic medium helps to convert KI to iodine, which can then react with N-bromosuccinimide. This reaction is commonly used to determine the vitamin C content in a solution.
KI
It might be because iodide and iodine is in an equilibrium: I2 + I- -> I3- That way formed iodine won't escape when an excess of iodide is used.
KI solution is commonly used in idiometric titrations because the presence of iodide ions allows for the detection of certain oxidizing agents through the formation of a characteristic color change with starch indicator. This method is particularly useful for determining the concentration of oxidizing agents such as chlorine or iodine in a sample solution.
ki is added to liberate iodine gas . this liberated iodine gas was then titrated with sodium thiosulphate to give a permanent white precipitate. this white precipitate indicates the endpoint of the titration..
On addition of the KI to your copper (II) solution, you formed Copper (I) iodine solid and produced the tri-iodide ion. It is the tri-iodide ion that you are titrating with the sodium thiosulfate. The tri-iodine ion is what itercalates into the starch molecules to form the dark blue color you are using as an end point in the titration. Some the the tri-iodide ion formed will adsorb to the surface of the solid copper (I) iodine formed. This must be desorbed for a complete titration. The addition of the potassium thiocyanate, displaces the adsorbed tri-iodine ion, and liberates it for titration.