Titration setup: the titrant drops from the burette into the analyte solution in the flask. An indicator present then changes color permanently at the endpoint.

Titration is a common laboratory method of quantitative/chemical analysis that can be used to determine the 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, of known concentration (a standard solution) and volume is used to react with a solution of the analyte, whose concentration is not known in advance. 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). Titrations can be classified by the type of reaction or type of indicator. ... For the chemical substances known as medicines, see medication. ... Tetration (also exponential map, hyperpower, power tower, super-exponentiation, and hyper4) is iterated exponentiation, the first hyper operator after exponentiation. ... diagram of modern burette A burette (also buret) is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. ... An Analyte is the substance or chemical constituent that is undergoing analysis. ... Erlenmeyer flasks from the Argonne National Laboratory glassblowing shop. ... Equivalence point or stoichiometric point occurs during a chemical titration when the amount of titrant added is equivalent, or equal, to the amount of analyte present in the sample. ... This article does not cite any references or sources. ... For other uses, see Concentration (disambiguation). ... A reactant or reagent is any substance initially present in a chemical reaction. ... A reactant or reagent is a substance consumed during a chemical reaction. ... Standard solution is a chemical term which describes a solution of known concentration. ... For other uses, see Volume (disambiguation). ... An Analyte is the substance or chemical constituent that is undergoing analysis. ... diagram of modern burette A burette (also buret) is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... A polyprotic acid is an acid that can dissociate to release more than one proton (hydrogen ion, H+). The first proton is the easiest to dissociate from the polyprotic acid, and each subsequent proton is less likely to dissociate. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit A...

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. Vision can refer to: Visual perception is one of the senses. ... Titration setup. ... Phenolphthalein is a sensitive chemical with the formula C20H14O4 (often written as HIn in shorthand notation). ... Methyl Orange is a pH indicator frequently used in titrations. ...

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. Redox titration (also called oxidation-reduction titration or potentiometric titration) is a type of titration based on a redox reaction between the analyte and titrant. ... Potassium permanganate is the chemical compound KMnO4. ...

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.

History and etymology

The word "titration" comes from the Latin word titalus, meaning inscription or title. The French word titre, also from this origin, means rank. Titration, by definition, is the determination of rank or concentration of a solution with respect to water with a pH of 7 (which is the pH of pure water).

The origins of volumetric analysis are in late-18th-century French chemistry. Francois Antoine Henri Descroizilles developed the first burette (which looked more like a graduated cylinder) in 1791. Joseph Louis Gay-Lussac developed an improved version of the burette that included a side arm, and coined the terms "pipette" and "burette" in an 1824 paper on the standardization of indigo solutions. A major breakthrough in the methodology and popularization of volumetric analysis was due to Karl Friedrich Mohr, who redesigned the burette by placing a clamp and a tip at the bottom, and wrote the first textbook on the topic, Lehrbuch der chemisch-analytischen Titrirmethode (Textbook of analytical-chemical titration methods), published in 1855.^[1] Joseph Louis Gay-Lussac. ... This article is about the laboratory instrument. ... Karl Friedrich Mohr (November 4, 1806 - September 28, 1879) was a German pharmacist famous for his early statement of the principle of conservation of energy. ...

Preparing a sample for titration

In a titration, both titrant and analyte are required to be aqueous, or in a solution form. If the sample is not a liquid or solution, the samples must be dissolved. If the analyte is very concentrated in the sample, it might be useful to dilute the sample. Drinking water This article focuses on water as we experience it every day. ...

Although the vast majority of titrations are carried out in aqueous solution, other solvents such as glacial acetic acid or ethanol (in petrochemistry) are used for special purposes. R-phrases , S-phrases , , , Flash point 43 °C Related Compounds Related carboxylic; acids Formic acid; Propionic acid; Butyric acid Related compounds acetamide; ethyl acetate; acetyl chloride; acetic anhydride; acetonitrile; acetaldehyde; ethanol; thioacetic acid; acetylcholine; acetylcholinesterase Supplementary data page Structure and properties n, εr, etc. ... Grain alcohol redirects here. ... Petrochemistry is the branch of chemistry that studies the transformation of crude oil (petroleum) and natural gas into usefull products and raw materials. ...

A measured amount of the sample can be given in the flask and then be dissolved or diluted. The mathematical result of the titration can be calculated directly with the measured amount. Sometimes the sample is dissolved or diluted beforehand, and a measured amount of the solution is used for titration. In this case the dissolving or diluting must be done accurately with a known coefficient because the mathematical result of the titration must be multiplied with this factor. For other senses of this word, see coefficient (disambiguation). ...

Many titrations require buffering to maintain a certain pH for the reaction. Therefore, buffer solutions are added to the reactant solution in the flask. For other uses, see PH (disambiguation). ... Acids and bases: Acid-base extraction Acid-base reaction Acid-base physiology Acid-base homeostasis Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non...

Some titrations require "masking" of a certain ion. This can be necessary when two reactants in the sample would react with the titrant and only one of them must be analysed, or when the reaction would be disturbed or inhibited by this ion. In this case another solution is added to the sample, which "masks" the unwanted ion (for instance by a weak binding with it or even forming a solid insoluble substance with it).

Some redox reactions may require heating the solution with the sample and titration while the solution is still hot (to increase the reaction rate). ed|other uses|reduction}} Illustration of a redox reaction Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... Iron rusting - a chemical reaction with a slow reaction rate. ...

Procedure

A typical titration begins with a beaker or Erlenmeyer flask containing a precise volume of the reactant and a small amount of indicator, placed underneath a burette containing the reagent. By controlling the amount of reagent added to the reactant, it is possible to detect the point at which the indicator changes colour. As long as the indicator has been chosen correctly, this should also be the point where the reactant and reagent neutralise each other, and, by reading the scale on the burette, the volume of reagent can be measured. A beaker is a simple container for liquids, very commonly used in laboratories. ... Conical flask For the episode of The X-Files, see The Erlenmeyer Flask. ... diagram of modern burette A burette (also buret) is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. ...

As the concentration of the reagent is known, the number of moles of reagent can be calculated (since concentration = moles / volume). Then, from the chemical equation involving the two substances, the number of moles present in the reactant can be found. Finally, by dividing the number of moles of reactant by its volume, the concentration is calculated.

Titration curves

It has been suggested that some content from this article be split into a separate article entitled Titration curve. (Discuss)

A typical titration curve of a diprotic acid, oxalic acid, titrated with a strong base, sodium hydroxide. Each of the two equivalence points are visible

Titrations are often recorded on titration curves, whose compositions are generally identical: the independent variable is the volume of the titrant, while the dependent variable is the pH of the solution (which changes depending on the composition of the two solutions). The equivalence point is a significant point on the graph (the point at which all of the starting solution, usually an acid, has been neutralized by the titrant, usually a base). It can be calculated precisely by finding the second derivative of the titration curve and computing the points of inflection (where the graph changes concavity); however, in most cases, simple visual inspection of the curve will suffice (in the curve given to the right, both equivalence points are visible, after roughly 15 and 30 mL of NaOH solution has been titrated into the oxalic acid solution.) To calculate the pKa values, one must find the volume at the half-equivalence point, that is where half the amount of titrant has been added to form the next compound (here, sodium hydrogen oxalate, then disodium oxalate). Halfway between each equivalence point, at 7.5 mL and 22.5 mL, the pH observed was about 1.5 and 4, giving the pKa values. Image File history File links No higher resolution available. ... In medicine, titration is the process of gradually adjusting the dose of a medication until the desired effect is achieved. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Oxalic acid (IUPAC name: ethanedioic acid, formula C2H2O4) is a dicarboxylic acid with structure (HOOC)-(COOH). ... Sodium hydroxide (NaOH), also known as lye, caustic soda and (incorrectly, according to IUPAC nomenclature)[1] sodium hydrate, is a caustic metallic base. ... In an experimental design, the independent variable (argument of a function, also called a predictor variable) is the variable that is manipulated or selected by the experimenter to determine its relationship to an observed phenomenon (the dependent variable). ... Titration setup. ... In experimental design, a dependent variable (also known as response variable, responding variable or regressand) is a factor whose values in different treatment conditions are compared. ... Equivalence point or stoichiometric point occurs during a chemical titration when the amount of titrant added is equivalent, or equal, to the amount of analyte present in the sample. ... In mathematics, the derivative is one of the two central concepts of calculus. ... In mathematics, particularly in calculus, a stationary point is a point on the graph of a function where the tangent to the graph is parallel to the x-axis or, equivalently, where the derivative of the function equals zero (known as a critical number). ... In calculus, a differentiable function f is convex on an interval if its derivative function f ′ is increasing on that interval: a convex function has an increasing slope. ... The millilitre (ml or mL, also spelt milliliter) is a metric unit of volume that is equal to one thousandth of a litre. ... Sodium hydroxide (NaOH), also known as lye, caustic soda and (incorrectly, according to IUPAC nomenclature)[1] sodium hydrate, is a caustic metallic base. ... Oxalic acid (IUPAC name: ethanedioic acid, formula C2H2O4) is a dicarboxylic acid with structure (HOOC)-(COOH). ... Disodium oxalate is a sodium salt of oxalic acid. ...

In monoprotic acids, the point halfway between the beginning of the curve (before any titrant has been added) and the equivalence point is significant: at that point, the concentrations of the two species (the acid and conjugate base) are equal. Therefore, the Henderson-Hasselbalch equation can be solved in this manner: An acid (often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... The Henderson-Hasselbalch (frequently misspelled Henderson-Hasselbach) equation in chemistry describes the derivation of pH as a measure of acidity (using pKa, the acid dissociation constant) in biological and chemical systems. ...

Therefore, one can easily find the acid dissociation constant of the monoprotic acid by finding the pH of the point halfway between the beginning of the curve and the equivalence point, and solving the simplified equation. In the case of the sample curve, the K_a would be approximately 1.78×10^-5 from visual inspection (the actual K_a2 is 1.7×10^-5) An acid dissociation constant, denoted by Ka, is an equilibrium constant for the dissociation of a weak acid. ...

For polyprotic acids, calculating the acid dissociation constants is only marginally more difficult: the first acid dissociation constant can be calculated the same way as it would be calculated in a monoprotic acid. The second acid dissociation constant, however, is the point halfway between the first equivalence point and the second equivalence point (and so on for acids that release more than two protons, such as phosphoric acid). A polyprotic acid is an acid that can dissociate to release more than one proton (hydrogen ion, H+). The first proton is the easiest to dissociate from the polyprotic acid, and each subsequent proton is less likely to dissociate. ... This article is about orthophosphoric acid. ...

Types of titrations

Titrations can be classified by the type of reaction. Different types of titration reaction include:

• Acid-base titrations are based on the neutralization reaction between the analyte and an acidic or basic titrant. These most commonly use a pH indicator, a pH meter, or a conductance meter to determine the endpoint.
• Redox titrations are based on an oxidation-reduction reaction between the analyte and titrant. These most commonly use a potentiometer or a redox indicator to determine the endpoint. Frequently either the reactants or the titrant have a colour intense enough that an additional indicator is not needed.
• Complexometric titrations are based on the formation of a complex between the analyte and the titrant. The chelating agent EDTA is very commonly used to titrate metal ions in solution. These titrations generally require specialized indicators that form weaker complexes with the analyte. A common example is Eriochrome Black T for the titration of calcium and magnesium ions.
• A form of titration can also be used to determine the concentration of a virus or bacterium. The original sample is diluted (in some 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. This value, the titre, may be based on TCID50, EID50, ELD50, LD₅₀ or pfu. This procedure is more commonly known as an assay.

Titration setup. ... Redox titration (also called oxidation-reduction titration or potentiometric titration) is a type of titration based on a redox reaction between the analyte and titrant. ... Complexometric titration is a type of titration based on complex formation between the analyte and titrant. ... Synthesis of copper(II)-tetraphenylporphine, a metal complex, from tetraphenylporphine and copper(II) acetate monohydrate. ... Chelation (from Greek, claw like) describes the reversible binding of an organic ligand, the chelator or chelating agent, to a metal ion, forming a metal complex, the chelate. ... EDTA is a widely-used acronym for the chemical compound ethylenediamine tetraacetic acid (and many other names, see table). ... A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. ... Eriochrome Black T Eriochrome Black T is a complexometric indicator that is part of the complexometric titrations, eg. ... For other uses, see Calcium (disambiguation). ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... This article is about biological infectious particles. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... A titer (or titre) is the unit in which the analytical detection of many substances is expressed. ... An LD50 test being administered In toxicology, the LD50 or colloquially semilethal dose of a particular substance is a measure of how much constitutes a lethal dose. ... A plaque forming unit (PFU) is a measure of the number of particles capable of forming plaques per unit volume, such as virus particles. ... An assay is a procedure where the concentration of a component part of a mixture is determined. ...

Measuring the endpoint of a titration

Main article: Endpoint (chemistry)

Different methods to determine the endpoint include: Equivalence point or stoichiometric point occurs during a chemical titration when the amount of titrant added is equivalent, or equal, to the amount of analyte present in the sample. ...

• pH indicator: This is a substance that changes colour in response to a chemical change. An acid-base indicator (e.g., phenolphthalein) changes colour depending on the pH. Redox indicators are also frequently used. A drop of indicator solution is added to the titration at the start; when the colour changes the endpoint has been reached.
• A potentiometer can also be used. This is an instrument that measures the electrode potential of the solution. These are used for titrations based on a redox reaction; the potential of the working electrode will suddenly change as the endpoint is reached.
• pH meter: This is a potentiometer that uses an electrode whose potential depends on the amount of H+ ion present in the solution. (This is an example of an ion-selective electrode. This allows the pH of the solution to be measured throughout the titration. At the endpoint, there will be a sudden change in the measured pH. It can be more accurate than the indicator method, and is very easily automated.
• Conductance: The conductivity of a solution depends on the ions that are present in it. During many titrations, the conductivity changes significantly. (For instance, during an acid-base titration, the H+ and OH- ions react to form neutral H₂O. This changes the conductivity of the solution.) The total conductance of the solution depends also on the other ions present in the solution (such as counter ions). Not all ions contribute equally to the conductivity; this also depends on the mobility of each ion and on the total concentration of ions (ionic strength). Thus, predicting the change in conductivity is harder than measuring it.
• Colour change: In some reactions, the solution changes colour without any added indicator. This is often seen in redox titrations, for instance, when the different oxidation states of the product and reactant produce different colours.
• Precipitation: If the reaction forms a solid, then a precipitate will form during the titration. A classic example is the reaction between Ag+ and Cl- to form the very insoluble salt AgCl. This usually makes it difficult to determine the endpoint precisely. As a result, precipitation titrations often have to be done as "back" titrations (see below).
• An isothermal titration calorimeter uses the heat produced or consumed by the reaction to determine the endpoint. This is important in biochemical titrations, such as the determination of how substrates bind to enzymes.
• Thermometric titrimetry is an extraordinarily versatile technique. This is differentiated from calorimetric titrimetry by the fact that 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 can be used to measure the absorption of light by the solution during the titration, if the spectrum of the reactant, titrant or product is known. The relative amounts of the product and reactant can be used to determine the endpoint.
• Amperometry can be used as a detection technique (amperometric titration). The current due to the oxidation or reduction of either the reactants or products at a working electrode will depend on the concentration of that species in solution. The endpoint can then be detected as a change in the current. This method is most useful when the excess titrant can be reduced, as in the titration of halides with Ag+. (This is handy also in that it ignores precipitates.)

Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit A... Phenolphthalein is a sensitive chemical with the formula C20H14O4 (often written as HIn in shorthand notation). ... For other uses, see PH (disambiguation). ... A redox indicator (also called an oxidation-reduction indicator or a potentiometric indicator) is an indicator that undergoes a definite colour change at a specific oxidation potential. ... It has been suggested that Determining emf of primary cells using potentiometer be merged into this article or section. ... This article may be too technical for most readers to understand. ... A pH meter is an electronic instrument used to measure the pH (acidity or basicity) of a liquid (though special probes are sometimes used to measure the pH of semi-solid substances, such as cheese). ... An ion selective electrode (ISE) is an electrode designed to respond to only one type of ion. ... Not to be confused with electrical conductance, a measure of an objects or circuits ability to conduct an electric current between two points, which is dependent on the electrical conductivity and the geometric dimensions of the conducting object. ... This article, image, template or category should belong in one or more categories. ... The ionic strength of a solution is a function of the concentration of all ions present in a solution. ... Precipitation is the condensation of a solid from a solution during a chemical reaction. ... A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity. ... Wöhler observes the synthesis of urea. ... For other uses, see Substrate. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Thermometric titration is one of a number of instrumental titration techniques where endpoints can be located accurately and precisely without a subjective interpretation on the part of the analyst as to their location. ... Animation of the dispersion of light as it travels through a triangular prism. ... This article deals with the general meaning of spectrum and the history of its use. ... Amperometric titration is method of titration used for measuring concentrations of certain substances in water using an electric current that flows during a chemical reaction. ...

Other terms

The term back titration is used when a titration is done "backwards": instead of titrating the original analyte, one adds a known excess of a standard reagent to the solution, then titrates the excess. A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration. They are also useful if the reaction between the analyte and the titrant is very slow. Back titration is an analytical chemistry technique which allows the user to find the concentration of a reactant of unknown concentration by reacting it with an excess volume of another reactant of known concentration. ...

Particular uses

• As applied to biodiesel, titration is the act of determining the acidity of a sample of WVO by the dropwise addition of a known base to the sample while testing with pH paper for the desired neutral pH=7 reading. By knowing how much base neutralizes an amount of WVO, we discern how much base to add to the entire batch.
• Titrations in the petrochemical or food industry to define oils, fats or biodiesel and similar substances. An example procedure for all three can be found here: [1].
  • Acid number: an acid-base titration with colour indicator is used to determine the free fatty acid content. See also: pH of fatty acids.
  • Iodine number: a redox titration with colour indication, which indicates the amount of unsaturated fatty acids.
  • Saponification value: an acid-base back titration with colour indicator or potentiometric to get a hint about the average chain length of fatty acids in a fat.

This article is about transesterified lipids. ... Acidity is a controversial novelette written for the popular South Asian website Chowk. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... For other uses, see PH (disambiguation). ... Petrochemicals are chemical products made from raw materials of petroleum (hydrocarbon) origin. ... The food industry is the complex, global collective of diverse businesses that together supply much of the food energy consumed by the world population. ... The acid number in chemistry is the mass of potassium hydroxide in milligrams that is required to neutralize one gram of chemical substance. ... Not to be confused with fats. ... Not to be confused with fats. ... The iodine number in chemistry is the mass of iodine in grams that is consumed by 100 grams of a chemical substance. ... Not to be confused with fats. ... Saponification value (or saponification number, also referred to as sap in short) represents the number of milligrams of potassium hydroxide or sodium hydroxide required to saponify 1g of fat under the conditions specified. ...

References

External links

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Titration

• Science aid: Titration An informative yet simple explanation of titration aimed at teens
• Titration - apparatus, technique and calculation
• Titration freeware - simulation of any pH vs. volume curve, distribution diagrams and real data analysis
• Free Metrohm Monograph: Practical Titration
• Free Metrohm Monograph: Practical Thermometric Titrimetry
• Basics of Titration: Free downloadable guide (pdf) from METTLER TOLEDO