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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
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:
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.
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 ...
An example of a secondary standard is sodium hydroxide, a hydroscopic compound that is highly reactive with its surroundings. The concentration of a standard solution made with sodium hydroxide may fluctuate overtime due to the instability of the compound, requiring for calibration using a primary standard before use.
A typical titration curve of a diprotic acid, oxalic acid, titrated with a strong base, sodium hydroxide.Both equivalence points are visible. Titrations are often recorded on graphs called titration curves, which generally contain the volume of the titrant as the independent variable and the pH of the solution as the dependent variable (because it changes depending on the composition of the ...
Gravimetric analysis describes a set of methods used in analytical chemistry for the quantitative determination of an analyte (the ion being analyzed) based on its mass. The principle of this type of analysis is that once an ion's mass has been determined as a unique compound, that known measurement can then be used to determine the same analyte's mass in a mixture, as long as the relative ...
Advantages of Coulometric Titration Coulometric titration has the advantage that constant current sources for the generation of titrants are relatively easy to make. The electrochemical generation of a titrant is much more sensitive and can be much more accurately controlled than the mechanical addition of titrant using a burette drive.