An endpoint titration is any scientific method that uses a titrant, titrand and sometimes an indicator solution to quantify the amount of reactant in a liquid substance. The endpoint is when enough titrant has been added to the titrand to facilitate a color change, or endpoint. The reactant can be quantified because the concentration of the titrant is known and the volumes of all solutions are recorded. An endpoint titration uses a calculation to determine the concentration of reactant in the solution. Every method requires a unique calculation to find its result.
What Is a Titrant?
A titrant is simply a liquid with a known value that is dropped into a sample, or titrand, until the titrand reaches its endpoint. For example, in a method testing for ammonia, a chemist can use 0.02 normal solution of sulfuric acid from a calibrated burette to neutralize a basic, as in not acidic, ammonia sample. When the acid drops turn the solution's color, the endpoint is reached. The titrant's volume is then recorded.
The titrand is the liquid, or sample, to be analyzed for a certain component like nitrogen or chloride. It is also what the titrant is dropped into to try and create the endpoint of the titration. Often the titrant has to go through a distillation or a digestion procedure before it is titrated for the component in question. In other words, sometimes the endpoint titration is only part of the scientific analysis.
Indicator solutions are not a necessary part of every endpoint titration. Sometimes the titrand is colored on its own and doesn't need an indicating solution. The purpose of an indicating solution is to show the endpoint of the titration. This is all dependent on the pH of the titrand. Once it reaches the pH where the indicator changes to another color, the test is finished.
Types of Endpoint Titrations
There are several types of titrations. The common acid-base example has an endpoint when the titrand is neutral or at a pH conducive for the indicator to change color. Oxidation and reduction titrations also have an obviously colorful endpoint. In addition, there are complexometric titrations that rely on the formation of compounds by the addition of the titrant to the solution in question.
Types of Instrumentation
For most titrations, a calibrated burette is all that is needed to measure the titrant. In other instances a spectrometer is required. A spectrometer can measure the wave length of a specific color at, and before, the endpoint. Sometimes the measurement is determined by a thermometer. In these cases the endpoint is actually a temperature rather than an amount of titrant.