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VOLUMETRIC ANALYSIS

 

Volumetric analysis, often known as titration, is a popular chemical analysis method that is quantitative and is used in laboratories to calculate specified analyte concentrations. The titrator or titrant is a reagent that is produced as a standard solution with a specified volume and concentration. To measure the analyte’s concentration, the titrant interacts with a solution of the analyte.

HISTORY OF VOLUMETRIC ANALYSIS

In the 1700s, the concept of volumetric analysis was developed to determine hydrogen sulfate, potash, and hypochlorite, all the solutions which were being used in the textile industry. Rather than determining precise concentrations, the initial methods devised were for practical objectives, such as controlling the quality of solutions. Étienne Henry, a French chemist, created the first genuine burette in 1845. Karl Mohr, who rebuilt an easy shape of the burette and created the first book on the subject in 1855, was responsible for a significant advance in the approach of titration (volumetric analysis).

PROCEDURE

A common titration starts with a flask or beaker containing a small amount of indicator (like thymol blue or phenolphthalein) placed below a calibrated burette. After that, a small amount of titrant is introduced to the indicator and the analyte until a change in the indicator's color is seen, indicating that the titration has reached its endpoint, which means that the quantity of titrant present equals the quantity of analyte present based on the interaction between them. Single drops of the titrant can create the difference between a temporary and permanent change in the color of the indicator, depending on the desired endpoint.

TITRATION CURVE

Titration curves are graphs that show the data collected by a titration. The information is shown on a two-dimensional axis, usually chemical volume on the horizontal and pH of the solution on the vertical axis. The curve of the graph shows the change in pH of the solution as the volume of the chemical changes due to the addition of the titrant. The chemical volume is an independent variable on the plot, while the pH is a dependent variable. The strength of the base and acid is represented by the titration curve of any acid-base titration. Near the equivalence point, the curve for a strong base and a strong acid will be quite steep. As a result, a little change in volume of the titrant at the equivalence point generates a high pH shift, and several suitable indicators can be utilized (like phenolphthalein, litmus, or bromothymol blue). The titration curve is uneven when out of base and acid. One of them is weak, and the other is strong, and the value of pH changes less with modest amounts of titrant at the equivalence point. Titrations between a weak base and a weak acid exhibit an extremely uneven titration curve. As a result, there may not be any suitable indicator, and, therefore, to analyze the reaction, a pH meter is used.

TYPES OF TITRATION

There are 4 types of titrations based on the nature of solvent and type of chemical reaction:

(1). Acid-Base Titration
It is a scientific method that estimates an acidic or basic solution's concentration precisely. It is based on the usage of a neutralization reaction as well as the fact that the pH of neutral (or nearly neutral) solutions varies quite quickly. The result is acquired in the form of neutralized pH value of 7.

(2). Redox Titration
This type of titration is based on the concept of a redox reaction, where one compound acts as an oxidizer and the other as a reducer. When the titration contains an oxidizer like potassium dichromate, then to calculate the endpoint of the titration, a redox indicator or potentiometer is generally used. An indicator like sodium diphenylamine is taken into use because initially, the color was orange, and then it changes to green, and this change of color is not certain. Iodine is utilized as an oxidizer in wine analysis to detect sulfur dioxide. In this example, starch is utilized as an indication; in the presence of sufficient iodine, a blue complex of starch and iodine forms, indicating the endpoint. Due to the constituents' deep color, there is no need for an indicator in certain redox titrations. For example, because of the color of the excess oxidizing agent KMnO4, a small persistent pink hue marks the endpoint of the titration.

(3). Precipitation Titration
The ability of these titrations to generate an insoluble precipitate throughout the reaction has made them notable. The precipitate may be seen easily at the flask's bottom. The evaluation of K2CO3 and K2SO4 in potash was one of the first precipitation titrations developed towards the end of the 18th century. The titrant was calcium nitrate(Ca(NO3)2) which formed a precipitate of CaCO3 and CaCO4.

(4). Complexometric Titration
Complex formation between the titrant and the analyte is required for complexometric titrations. They often require the use of specific complexometric indicators. With the analyte, these indicators create weak complexes. For example, by Improving iodometric titration sensitivity using starch as an indicator, the deep blue complex of starch with iodine and iodide is more visible than iodine alone.

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