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Requirements For Titrimetric Analysis
For use in titrimetric analysis a reaction must fulfil the following conditions.
- There must be a simple reaction which can be expressed by a chemical equation; the substance to be determined should react completely with the reagent in stoichiometric or equivalent proportions.
- The reaction should be relatively fast. (Most ionic reactions satisfy this condition.) In some cases the addition of a catalyst may be necessary to increase the speed of a reaction.
- There must be an alteration in some physical or chemical property of the solution at the equivalence point.
An indicator should be available which, by a change in physical properties (colour or formation of a precipitate), should sharply define the end point of the reaction. If no visible indicator is available, the detection of the equivalence point can often be achieved by following the course of the titration by measuring
(a) The potential between an indicator electrode and a reference electrode (potentiornetric titration);
(b) The change in electrical conductivity of the solution (conductirnetric titration);
(c) The current which passes through the titration ce11 between an indicator electrode and a depolarised reference electrode at a suitable applied e.m.f. (arnperometric titration);
(d) the change in absorbance of the solution (spectrophotornetric titration).
- Titrimetric methods are normally capable of high precision (1 part in 1000) and wherever applicable possess obvious advantages over gravimetric methods. They need simpler apparatus, and are, generally, quickly performed; tedious and difficult separations can often be avoided.
Basic principles of volumetric analysis
- The solution to be analysed contains an unknown amount of chemicals.
- The reagent of unknown concentration reacts with a chemical of an unknown amount in the presence of an indicator (mostly phenolphthalein) to show the end-point. It’s the point indicating the completion of the reaction.
- The volumes are measured by titration which completes the reaction between the solution and reagent.
- The volume and concentration of reagent which are used in the titration show the amount of reagent and solution.
The amount of unknown chemical in the specific volume of solution is determined by the mole fraction of the equation.
When the endpoint of the reaction is reached, the volume of reactant consumed is measured and applied to carry volumetric analysis calculations of the analyte by the following formula,
- Ca= Ct Vt M / Va
- Where,
- Ca is the analyte concentration, typically in molarity.
- Ct is the titrant concentration, typically in molarity.
- V is the volume of the titrant which is used, typically in liters.
- M is the mole ratio of the analyte and reactant from the balanced equation.
- V is the volume of the analyte, typically in liters.
Many non-acid-base titrations are needed a constant pH throughout the reaction. Therefore, a buffer solution can be added to the titration chamber to maintain the pH value.