Volumetric analysis: complete expression for stoichiometric calculations.

Abstract

The aim of a volumetric titration is to find the analyte concentration from the consumed volume of titrant and its molarity. For calculations, the use of stoichiometric factors is compulsory if the concentration is expressed in moles/liter. When analyte and titrant react with each other during the titration, the stoichiometric factor is just the stoichiometric coefficients ratio for both in the chemical equation. It happens so in the titration of HCl with sodium carbonate. Sometimes, analyte and titrant take part in a chain of reactions in which the former is chemically converted to a titrable species. This is the case of Cu(II) titration with thiosulfate: Cu(II) ions react first with excess iodide to yield I2 which is titrated with a thiosulfate solution of known molarity. In these instances, a relationship between the moles of analyte and moles of titrant should be established as the stoichiometric factor. In this exercise, the data from a volumetric titration are converted finally to mass percent of analyte in the sample. It is solved by dragging and dropping pieces (expressing concepts) on a complete stoichiometric equation which returns amount of mass every time a chemical meaning product is set up.