Is a quantitative analysis of concentration of an unknown acid or base solution. Titration, also known as titrimetry, is a common laboratory method of that is used to determine the unknown of an identified. Since measurements play a key role in titration, it is also known as volumetric analysis. A, called the titrant or titrator is prepared as a. A known concentration and volume of titrant reacts with a solution of analyte or titrand to determine concentration. The volume of titrant reacted is called titration volume. Contents • • • • • • • • • • • • • • • • • • • • • • History and etymology [ ] The word 'titration' descends from the French word tiltre (1543), meaning the 'proportion of gold or silver in coins or in works of gold or silver'; i.e., a measure of fineness or purity.

Tiltre became titre, which thus came to mean the 'fineness of alloyed gold', and then the 'concentration of a substance in a given sample'. In 1828, the French chemist Gay-Lussac first used titre as a verb ( titrer), meaning 'to determine the concentration of (a substance in a given sample)'. Volumetric analysis originated in late 18th-century France. () developed the first burette (which was similar to a graduated cylinder) in 1791. Developed an improved version of the burette that included a side arm, and coined the terms ' and ' in an 1824 paper on the standardization of indigo solutions.

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The first true burette was invented in 1845 by the French chemist (1798–1873). A major breakthrough in the methodology and popularization of volumetric analysis was due to, who redesigned the burette into a simple and convenient form, and who wrote the first textbook on the topic, Lehrbuch der chemisch-analytischen Titrirmethode ( Textbook of analytical chemistry titration methods), published in 1855. Procedure [ ]. A typical titration curve of a acid titrated with a strong base.

Shown here is titrated with. Both equivalence points are visible. A titration curve is a curve in the plane whose x-coordinates are the volume of added since the beginning of the titration, and whose y-coordinate is the concentration of the analyte at the corresponding stage of the titration (in an acid–base titration, the y-coordinate is usually the pH of the solution).

In an – titration, the titration curve reflects the strength of the corresponding acid and base. For a strong acid and a strong base, the curve will be relatively smooth and very steep near the equivalence point. Because of this, a small change in titrant volume near the equivalence point results in a large pH change and many indicators would be appropriate (for instance, or ). If one reagent is a weak acid or base and the other is a strong acid or base, the titration curve is irregular and the pH shifts less with small additions of titrant near the equivalence point.

For example, the titration curve for the titration between (a weak acid) and (a strong base) is pictured. The equivalence point occurs between pH 8-10, indicating the solution is basic at the equivalence point and an indicator such as would be appropriate. Titration curves corresponding to weak bases and strong acids are similarly behaved, with the solution being acidic at the equivalence point and indicators such as and being most appropriate. Titrations between a weak acid and a weak base have titration curves which are highly irregular. Because of this, no definite indicator may be appropriate and a is often used to monitor the reaction. The type of function that can be used to describe the curve is called a. Types of titrations [ ] There are many types of titrations with different procedures and goals.

The most common types of qualitative titration are and. Acid–base titration [ ].

Methyl orange Indicator Color on acidic side Range of color change Color on basic side Methyl violet Yellow 0.0–1.6 Violet Bromophenol blue Yellow 3.0–4.6 Blue Methyl orange Red 3.1–4.4 Yellow Methyl red Red 4.4–6.3 Yellow Litmus Red 5.0–8.0 Blue Bromothymol blue Yellow 6.0–7.6 Blue Phenolphthalein Colorless 8.3–10.0 Pink Alizarin yellow Yellow 10.1–12.0 Red Acid–base titrations depend on the between an acid and a base when mixed in solution. In addition to the sample, an appropriate is added to the titration chamber, reflecting the pH range of the equivalence point. The acid–base indicator indicates the endpoint of the titration by changing color. The endpoint and the equivalence point are not exactly the same because the equivalence point is determined by the stoichiometry of the reaction while the endpoint is just the color change from the indicator.

Thus, a careful selection of the indicator will reduce the indicator error. For example, if the equivalence point is at a pH of 8.4, then the Phenolphthalein indicator would be used instead of Alizarin Yellow because phenolphthalein would reduce the indicator error. Common indicators, their colors, and the pH range in which they change color are given in the table above. When more precise results are required, or when the reagents are a weak acid and a weak base, a or a conductance meter are used. For very strong bases, such as,, and, water is generally not a suitable solvent and indicators whose are in the range of aqueous pH changes are of little use. Instead, the titrant and indicator used are much weaker acids, and anhydrous solvents such as are used.

Main article: Redox titrations are based on a between an oxidizing agent and a reducing agent. A or a is usually used to determine the endpoint of the titration, as when one of the constituents is the oxidizing agent. The color change of the solution from orange to green is not definite, therefore an indicator such as sodium diphenylamine is used. Analysis of wines for requires iodine as an oxidizing agent. In this case, starch is used as an indicator; a blue starch-iodine complex is formed in the presence of excess iodine, signalling the endpoint. Some redox titrations do not require an indicator, due to the intense color of the constituents. For instance, in a slight persisting pink color signals the endpoint of the titration because of the color of the excess oxidizing agent.

In, at sufficiently large concentrations, the disappearance of the deep red-brown ion can itself be used as an endpoint, though at lower concentrations sensitivity is improved by adding, which forms an intensely blue complex with triiodide. Color of titration mixture before (left) and after (right) the end point Gas phase titration [ ] Gas phase titrations are titrations done in the, specifically as methods for determining reactive species by reaction with an excess of some other gas, acting as the titrant.

In one common gas phase titration, gaseous is titrated with nitrogen oxide according to the reaction O 3 + NO → O 2 + NO 2. After the reaction is complete, the remaining titrant and product are quantified (e.g., by ); this is used to determine the amount of analyte in the original sample. Gas phase titration has several advantages over simple. First, the measurement does not depend on path length, because the same path length is used for the measurement of both the excess titrant and the product. Second, the measurement does not depend on a linear change in absorbance as a function of analyte concentration as defined by the.

Third, it is useful for samples containing species which interfere at wavelengths typically used for the analyte. Complexometric titration [ ]. Main article: Complexometric titrations rely on the formation of a between the analyte and the titrant. In general, they require specialized that form weak complexes with the analyte. The most common example is the use of to increase the sensitivity of iodometric titration, the dark blue complex of starch with iodine and iodide being more visible than iodine alone. Other complexometric indicators are for the titration of and ions, and the used to titrate metal ions in solution. Zeta potential titration [ ].

Main articles: and An assay is a form of biological titration used to determine the concentration of a. Serial dilutions are performed on a sample in a fixed ratio (such as 1:1, 1:2, 1:4, 1:8, etc.) until the last dilution does not give a positive test for the presence of the virus. The positive or negative value may be determined by visually inspecting the infected cells under a or by an immunoenzymetric method such as (ELISA). This value is known as the. Measuring the endpoint of a titration [ ]. Main article: Different methods to determine the endpoint include: • Indicator: A substance that changes color in response to a chemical change. An (e.g., ) changes color depending on the pH.

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. •: An instrument that measures the of the solution. These are used for redox titrations; the potential of the working electrode will suddenly change as the endpoint is reached. An elementary that can be used to monitor titration reactions •: A potentiometer with an electrode whose potential depends on the amount of H + ion present in the solution.

(This is an example of an.) 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. •: 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 + and OH − ions react to form neutral H 2O.) As total conductance depends on all ions present in the solution and not all ions contribute equally (due to and ), 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.

•: If a reaction produces a solid, a precipitate will form during the titration. A classic example is the reaction between Ag + and Cl − 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). •: An instrument that measures the heat produced or consumed by the reaction to determine the endpoint. Used in titrations, such as the determination of how bind to. •: 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. •: Used to measure the absorption of light by the solution during titration if the of the reactant, titrant or product is known. The concentration of the material can be determined. •: 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 with Ag +. Endpoint and equivalence point [ ] Though equivalence point and endpoint are 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 of titrant is equal to the number of moles of analyte, or some multiple thereof (as in acids). Endpoint is what is actually measured, a physical change in the solution as determined by an or an instrument mentioned above.

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. 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 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- solid.

Graphical methods [ ] The titration process creates solutions with compositions ranging from pure acid to pure base. Identifying the pH associated with any stage in the titration process is relatively simple for monoprotic acids and bases. The presence of more than one acid or base group complicates these computations. Graphical methods, such as the equiligraph, have long been used to account for the interaction of coupled equilibria. These graphical solution methods are simple to implement, however they are infrequently used.

Particular uses [ ]. A titration is demonstrated to secondary school students.

Acid–base titrations [ ] • In: (WVO) must be neutralized before a batch may be processed. A portion of WVO is titrated with a base to determine acidity, so the rest of the batch may be properly neutralized. This removes from the WVO that would normally react to make soap instead of biodiesel. •: a measure of nitrogen content in a sample. Organic nitrogen is digested into with and. Finally, ammonia is back titrated with and then.

•: the mass in milligrams of (KOH) required to titrate fully an acid in one gram of sample. An example is the determination of content. •: the mass in milligrams of KOH required to saponify a in one gram of sample. Saponification is used to determine average chain length of fatty acids in fat.

• Ester value (or ester index): a calculated index. Ester value = Saponification value – Acid value. • Amine value: the mass in milligrams of KOH equal to the content in one gram of sample.

•: the mass in milligrams of KOH corresponding to groups in one gram of sample. The analyte is using then titrated with KOH. Redox titrations [ ] •: Used to determine oxygen concentration in water. Oxygen in water samples is reduced using, which reacts with to produce. The iodine is released in proportion to the oxygen in the sample, thus the oxygen concentration is determined with a redox titration of iodine with using a starch indicator.

•: Also known as ascorbic acid, vitamin C is a powerful reducing agent. Its concentration can easily be identified when titrated with the blue dye Dichlorophenolindophenol () which turns colorless when reduced by the vitamin. •: Excess in urine may indicate in the patient. Benedict's method is the conventional method to quantify glucose in urine using a prepared reagent. In this titration, glucose reduces ions to cuprous ions which react with to produce a white precipitate, indicating the endpoint. •: A measure of in an analyte, expressed in milligrams of bromine absorbed by 100 grams of sample.

•: A measure of unsaturation in an analyte, expressed in grams of iodine absorbed by 100 grams of sample. Miscellaneous [ ] •: A potentiometric method to analyze trace amounts of water in a substance.

A sample is dissolved in, and titrated with Karl Fischer reagent. The reagent contains iodine, which reacts proportionally with water. Thus, the water content can be determined by monitoring the of excess iodine. See also [ ] • References [ ].