Editing Titration (section)

==Measuring the endpoint of a titration==
{{main|Equivalence point}}
Different methods to determine the endpoint include:<ref>
{{Cite encyclopedia
  | title = Titration
  | encyclopedia = Science & Technology Encyclopedia
  | publisher = McGraw-Hill
  | url = http://www.answers.com/topic/titration
  | access-date = 30 September 2011
}}</ref>
*Indicator: A substance that changes color in response to a chemical change. An [[pH indicator|acid–base indicator]] (e.g., [[phenolphthalein]]) changes color depending on the pH. [[Redox indicator]]s are also used. A drop of indicator solution is added to the titration at the beginning; the endpoint has been reached when the color changes.
*[[Potentiometer (measuring instrument)|Potentiometer]]: An instrument that measures the [[electrode potential]] of the solution.  These are used for redox titrations; the potential of the working electrode will suddenly change as the endpoint is reached.
[[File:PHmeter basic.JPG|thumb|An elementary [[pH meter]] that can be used to monitor titration reactions.]]
*[[pH meter]]: A potentiometer with an electrode whose potential depends on the amount of H<sup>+</sup> ion present in the solution. (This is an example of an [[ion-selective electrode]].) The pH of the solution is measured throughout the titration, more accurately than with an indicator; at the endpoint there will be a sudden change in the measured pH.
*[[electrical conductivity|Conductivity]]: A measurement of ions in a solution.  Ion concentration can change significantly in a titration, which changes the conductivity. (For instance, during an acid–base titration, the H<sup>+</sup> and OH<sup>−</sup> ions react to form neutral H<sub>2</sub>O.) As total conductance depends on all ions present in the solution and not all ions contribute equally (due to [[electrophoretic mobility|mobility]] and [[ionic strength]]), predicting the change in conductivity is more difficult than measuring it.
*Color change: In some reactions, the solution changes color without any added indicator. This is often seen in redox titrations when the different oxidation states of the product and reactant produce different colors.
*[[Precipitation (chemistry)|Precipitation]]: If a reaction produces a solid, a precipitate will form during the titration. A classic example is the reaction between Ag<sup>+</sup> and Cl<sup>−</sup> to form the insoluble salt AgCl. Cloudy precipitates usually make it difficult to determine the endpoint precisely. To compensate, precipitation titrations often have to be done as "back" titrations (see below).
*[[Calorimeter#Isothermal titration calorimeter|Isothermal titration calorimeter]]: An instrument that measures the heat produced or consumed by the reaction to determine the endpoint.  Used in [[biochemistry|biochemical]] titrations, such as the determination of how [[substrate (biochemistry)|substrate]]s bind to [[enzyme]]s.
*[[Thermometric Titration|Thermometric titrimetry]]: Differentiated from calorimetric titrimetry because the heat of the reaction (as indicated by temperature rise or fall) is not used to determine the amount of analyte in the sample solution. Instead, the endpoint is determined by ''the rate of temperature change''.
*[[Spectroscopy]]: Used to measure the absorption of light by the solution during titration if the [[spectrum]] of the reactant, titrant or product is known.  The concentration of the material can be determined by [[Beer's Law]].
*[[amperometric titration|Amperometry]]: Measures the current produced by the titration reaction as a result of the oxidation or reduction of the analyte. The endpoint is detected as a change in the current. This method is most useful when the excess titrant can be reduced, as in the titration of [[halide]]s with Ag<sup>+</sup>.

===Endpoint and equivalence point===
Though the terms equivalence point and endpoint are often used interchangeably, they are different terms.  ''Equivalence point'' is the theoretical completion of the reaction: the volume of added titrant at which the number of [[Mole (unit)|moles]] of titrant is equal to the number of moles of analyte, or some multiple thereof (as in [[polyprotic]] acids).  ''Endpoint'' is what is actually measured, a physical change in the solution as determined by an [[pH indicator|indicator]] or an instrument mentioned above.<ref>
{{Cite book
  | last = Harris
  | first = D.C.
  | title = Quantitative Chemical Analysis
  | publisher = Macmillan
  | edition = 6
  | year = 2003
  | pages = 129
  | isbn = 0-7167-4464-3
}}</ref>

There is a slight difference between the endpoint and the equivalence point of the titration. This error is referred to as an indicator error, and it is indeterminate.<ref>
{{Cite book
  | last = Hannan
  | first = H.J.
  | title = Technician's Formulation Handbook for Industrial and Household Cleaning Products
  | publisher = Lulu.com
  | year = 2007
  | pages = 103
  | isbn = 978-0-615-15601-9
}}{{self-published source|date=February 2020}}</ref>{{self-published inline|date=February 2020}}

===Back titration===
Back titration is a titration done in reverse; instead of titrating the original sample, a known excess of standard reagent is added to the solution, and the excess is titrated. A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration, as with [[Precipitation (chemistry)|precipitation]] reactions. Back titrations are also useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in a non-[[Solubility|soluble]] solid.<ref>
{{Cite book
  | last = Kenkel
  | first = J.
  | title = Analytical Chemistry for Technicians
  | publisher = CRC Press
  | volume = 1
  | edition = 3
  | year = 2003
  | pages = 108–109
}}</ref>