Volumetric Analysis | An Introduction
Volumetric analysis is one of the major branches of chemical analysis. It involves calculations which are based on simple stoichiometric equations. Volumetric analysis also require accurate measurement of volume. The advantages of the this technique are numerous eg: [li]easy to carry out[/li] [li]versatile and reliable[/li] [li]many of the reagents are cheap[/li] [li]vast range of applications[/li] [b] Terminology[/b] [b]Analyte:[/b] solution of unknown concentration [b]Titrant or Standard Solution:[/b] reactant will be a solution or known concentration [b]Equivalence Point:[/b] is the moment when two solutions are reacted together until the reaction is precisely completed [b]End Point:[/b] Experimental estimates of the equivalence point and should be as close as possible to the end point [b]Indicator:[/b] substance that indicates the end point , usually by changing colour [b]Key Factors to Consider for Volumetric Analysis[/b] [li]The reaction must proceed according to a definite chemical equation with no side reactions[/li] [li]The reaction should proceed to virtual completion at the equivalence point - this means that the concentration of one of the reactants increases dramatically after the equivalence point[/li] [li]There must be some method of detecting the equivalence point - an indicator or electrical method[/li] [li]The reaction should be rapid so that the titration can be completed in a few minutes[/li] [b]Reactions Used in Titrations[/b] 1. Acid - Base Reactions eg H[sub]3[/sub]O[sup]+[/sup] + OH[sup]-[/sup] ---> 2H[sub]2[/sub]O Most systems are aqueous ie solutions in water, although some compounds require a different solvent for the analyisis eg. Morphine, caffeine 2. Redox Reactions (Oxidation - Reduction) These are electron transfer reactions eg Fe[sup]2+[/sup] + Ce[sup]4+[/sup] ------> Fe[sup]3+[/sup] + Ce[sup]3+[/sup] 3. Precipitation Reactions These are usually analysis of the halide ions (Cl[sup]-[/sup], Br[sup]-[/sup], I[sup]-[/sup]) using Ag[sup]+[/sup] ions Ag[sup]+[/sup] + X[sup]-[/sup] --------> AgX(s) 4. Complexometric Reactions - Formation of Metal Complexes Used in the determination of many metal ions. The most common reagent is EDTA (ethylenediaminetetraacetic acid) Reacts with metal ions in a 1:1 ratio M[sup]n+[/sup] + EDTA[sup]4- [/sup] --------> M(EDTA)[sup](n-4)+[/sup] Next---> Acid Base Reactions [a href="?id=1012-160-1&t=Acid-Base-Reactions"]next[/a] Contributed by Nuruddin Boateng- MBCS,MNZCS,MSc IT,BSc(Hons)Chemistry, Dip Ed.
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