3.7.1. BASIC PRINCIPLES
In titrimetric analysis we volumetrically measure the amount of reagent, often called a titrant, required to complete a chemical reaction with the analyte.
A generic chemical reaction for titrimetric analysis is
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Where: a moles of analyte A contained in the sample reacts with t moles of the titrant T in the titrant solution.
The reaction is generally carried out in a flask containing the liquid or dissolved sample.
Titrant solution is volumetrically delivered to the reaction flask using a burette.
Delivery of the titrant is called a titration.
The titration is complete when sufficient titrant has been added to react with all the analyte. This is called the equivalence point.
An indicator is often added to the reaction flask to signal when all of the analyte has reacted.
The titrant volume where the signal is generated is called the end point.
The equivalence and end points are rarely the same.
SUCCESSFUL TITRATIONS
A few rules of thumb for designing a successful titration are: 1. The titrant should either be a standard or should be standardized. 2. The reaction should proceed to a stable and well defined equivalence point. 3. The equivalence point must be able to be detected. 4. The titrant’s and sample’s volume or mass must be accurately known. 5. The reaction must proceed by a definite chemistry. There should be complicating side reactions. 6. The reaction should be nearly complete at the equivalence point. In other words, chemical equilibrium favors products. 7. The reaction rate should be fast enough to be practical.
TYPES OF TITRATIONS
1. ACID-BASE TITRATION
a. These titrations are based on the neutralization reaction that occurs between an acid and a base, when mixed in solution. b. The acid (resp. base) is added to a burette c. Burette which was rinsed with the same acid prior to this addition [prevent contamination or diluting of the acid being measured d. The base (resp. acid) is added to a volumetric flask e. Volumetric flask which had been rinsed with distilled water prior to the addition f. Solution in the volumetric flask is often a standard solution[concentration is exactly known] g. Indicator used often depends on the nature of the constituents h. When more precise results are required, or when the titration constituents are a weak acid and a weak base, a pH meter or a conductance meter are used.
