Titration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the titrant or titrator[1], of known concentration (a standard solution) and volume is used to react with a solution of the analyte or titrand[2], whose concentration is not known. Using a calibrated burette to add the titrant, it is possible to determine the exact amount that has been consumed when the endpoint is reached. The endpoint is the point at which the titration is complete, as determined by an indicator (see below). This is ideally the same volume as the equivalence point - the volume of added titrant at which the number of moles of titrant is equal to the number of moles of analyte, or some multiple thereof (as in polyprotic acids). In the classic strong acid-strong base titration, the endpoint of a titration is the point at which the pH of the reactant is just about equal to 7, and often when the solution permanently changes color due to an indicator. There are however many different types of titrations (see below).
Many methods can be used to indicate the endpoint of a reaction; titrations often use visual indicators (the reactant mixture changes colour). In simple acid-base titrations a pH indicator may be used, such as phenolphthalein, which becomes pink when a certain pH (about 8.2) is reached or exceeded. Another example is methyl orange, which is red in acids and yellow in alkali solutions.
Not every titration requires an indicator. In some cases, either the reactants or the products are strongly coloured and can serve as the "indicator". For example, an oxidation-reduction titration using potassium permanganate (pink/purple) as the titrant does not require an indicator. When the titrant is reduced, it turns colourless. After the equivalence point, there is excess titrant present. The equivalence point is identified from the first faint pink color that persists in the solution being titrated.
Due to the logarithmic nature of the pH curve, the transitions are, in general, extremely sharp; and, thus, a single drop of titrant just before the endpoint can change the pH significantly — leading to an immediate colour change in the indicator. There is a slight difference between the change in indicator color and the actual equivalence point of the titration. This error is referred to as an indicator error, and it is indeterminate.
滴定是定量化学分析中常见的实验室方法，用于测定已知反应物的未知浓度。因为体积计量在滴定中发挥关键作用，所以又称为容量分析。一种叫作滴定液的浓度和体积已知的试剂（标准溶液）与未知浓度的被测物或被滴定物反应。用经过校正的滴定管加入滴定液，就有可能测定到达终点时滴定液的确切消耗量。终点是滴定完成时所处的点，由指示剂（见页底）来测定。理想中，这与等当点的体积相同。等当点是滴定液的摩尔数等于或几倍于（比如，多元酸）被测物摩尔数时所加入的滴定液的体积。在古典强酸－强碱滴定中，滴定终点为反应物PH值约等于7时的点，也就是由于指示剂作用，溶液颜色变化稳定之时的点。然而，滴定有多种不同型式。
多种方法都能用于指示反应终点：滴定常常使用视觉指示剂（反应混合物颜色发生变化）。在简单酸－碱滴定中，可使用PH指示剂，如酚酞。当达到或超过某一PH（约为8.2）时，它变成红色。另一个例子是甲基橙，它在酸性溶液中为红色而在碱性溶液中为黄色。
并非每一种滴定都需要指示剂。有些情况下，反应物或生成物都有很强烈的颜色，可用作“指示剂”。例如，一种以高锰酸钾（粉红或紫色）为滴定液的氧化－还原滴定就不需要指示剂。当滴定液被还原时，它就变成无色。等当点之后，有多余的滴定液出现。可从第一次出现在正在被滴定的溶液中的稳定的微红色来鉴别等当点。
由于PH曲线的对数性质，一般而言转变是非常明显的，因此，等当点之前的一滴滴定液能使PH发生显著变化，引进指示剂颜色突变。指示剂颜色的改变与真实等当点之间存在着微小差异。这个误差被称为指示剂误差，而这个误差是不确定的。
