The titration method determines the unknown concentration of a substance (called the analyte) in a mixture of known volume or weight, by adding a reactant of known concentration (called the titrant) to the mixture that reacts specifically with the analyte. By determining the exact amount of titrant it takes to react with all the analyte it is possible to calculate the concentration of the analyte in the mixture. Titration has some distinct advantages over other techniques for certain types of analyses, such as alkalinity and acidity. Titration is also less susceptible to errors due to colored or particulate samples than colorimetric methods.
A + T -> P
A titration measurement requires reacting two chemicals, usually in solution, to form a product. One of the reactants has a known concentration and is called the titrant (labeled T) The other reactant is the one we are trying to quantify in a mixture and is called the analyte (labeled A). The product of the reaction is labeled P. There are certain conditions that must be true for a titration to work:
The titrant, T, should have a preference for reacting with only the analyte, A, and not with other chemicals that may be in the mixture. Examples: hydrogen ions (H+) preferably react with hydroxide ions (OH-) in an acid base titration; silver ions (Ag+) preferably react with chloride ions (Cl-) in a salt titration in cheese; ethylene diamine tetraacetic acid (EDTA) preferably reacts with calcium ions (Ca2+)in a water hardness titration.The ratio between the number of molecules of titrant that react with each molecule of analyte must be known. This is known as the stoichiometry of the reaction. Examples: one molecule of Ag+ reacts with exactly one molecule of Cl- to form silver chloride (AgCl); two molecules of Ag+ react with exactly one molecule of sulfide ion (S2-)to form Ag2S.The concentration of the titrant (T) must be accurately known.The volume (or sometimes weight) of the sample mixture must be accurately known. Again, this will be needed in calculating the concentration of the unknown analyte in the sample.A sensor is needed to detect changes in concentration of either one of the reactants (T or A) or the product (P) to determine precisely when just the right amount of titrant (T) has been added to the mixture to react with all the analyte (A). This is called the end point (or equivalence point) of the titration, and will be described more thoroughly in the next section. The sensor can be as simple as your eyeball in detecting a sudden change in color, to as sophisticated as an electrochemical sensor.Finally, we need a device to accurately measure the amount of titrant (T) that is being added to the sample mixture. Once the end point has been detected by the sensor, you will then need to refer to this measuring device to determine how much titrant has been added. There are various types of instruments for measuring the volume of a titrant, from simple eyedroppers to automatic burettes
