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An example of back titration, the Volhard method, named after Jacob Volhard, involves the addition of excess silver nitrate to the analyte; the silver chloride is filtered, and the remaining silver nitrate is titrated against ammonium thiocyanate, [1] with ferric ammonium sulfate as an indicator which forms blood-red [Fe(OH 2) 5 (SCN)] 2+ at the end point:
Back titration is a titration done in reverse; instead of titrating the original sample, a known excess of standard reagent is added to the solution, and the excess is titrated. A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration, as with precipitation reactions ...
Thus, one standard solution is needed (e.g. HCl) in the direct titration, while two are needed (e.g. HCl and NaOH) in the back-titration. One of the suitable indicators for these titration reactions is Tashiro's indicator. [3] In practice, this analysis is largely automated; specific catalysts accelerate the decomposition. Originally, the ...
The volumetric titration is based on the same principles as the coulometric titration, except that the anode solution above now is used as the titrant solution. The titrant consists of an alcohol (ROH), base (B), SO 2 and a known concentration of I 2. Pyridine has been used as the base in this case. One mole of I 2 is consumed for each mole of ...
Fig. 15. Titration plot of back-titration of excess EDTA with Cu(II) in NH 3 /NH 4 Cl buffered solution. Direct EDTA titrations with metal ions are possible when reaction kinetics are fast, for example zinc, copper, calcium and magnesium. However, with slower reaction kinetics such as those exhibited by cobalt and nickel, back-titrations are used.
The interplay of the intrinsic pK a values of a system with the electrostatic interaction energies between titratable groups can produce quite spectacular effects such as non-Henderson–Hasselbalch titration curves and even back-titration effects. [6] The image on the right shows a theoretical system consisting of three acidic residues.
Some examples of primary standards for titration of solutions, based on their high purity, are provided: [4] Arsenic trioxide for making sodium arsenite solution for standardisation of sodium periodate solution (until Ph. Eur. 3, Appendix 2001 also for iodine and cerium(IV) sulfate solutions, since Ph. Eur. 4, 2002 standardised by sodium ...
A drop of indicator solution is added to the titration at the start; when the color changes the endpoint has been reached, this is an approximation of the equivalence point. Conductance The conductivity of a solution depends on the ions that are present in it. During many titrations, the conductivity changes significantly.