Titration setup: the titrant drops from the burette into the analyte solution in the flask. 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 An analyte is a substance or Chemical constituent that is determined in an analytical procedure such as a Titration. Laboratory flasks are vessels (containers which fall into the category of Laboratory equipment known as glassware. An indicator present then changes color permanently at the endpoint. Equivalence point or stoichiometric point occurs during a chemical Titration when the amount of Titrant added is equivalent or equal to the amount of

Titration is a common laboratory method of quantitative/chemical analysis that can be used to determine the concentration of a known reactant. Analytical chemistry is the study of the Chemical composition of natural and artificial Materials. In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance A reagent or reactant is a substance or compound consumed during a Chemical reaction. 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. A reagent or reactant is a substance or compound consumed during a Chemical reaction. Standard solution is a chemical term which describes a Solution of known Concentration. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically An analyte is a substance or Chemical constituent that is determined in an analytical procedure such as a Titration. 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. 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 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). The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are 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. A pH indicator is a halochromic chemical compound that is added in small amounts to a Solution so that the PH ( Acidity or 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). The visual system is the part of the Nervous system which allows organisms to see. In simple acid-base titrations a pH indicator may be used, such as phenolphthalein, which becomes pink when a certain pH (about 8. An acid-base Titration is a method in Chemistry that allows quantitative analysis of the concentration of an unknown Acid or base Phenolphthalein is a Chemical compound with the formula C 20 H 14 O 4 (often written as " HIn 2) is reached or exceeded. Another example is methyl orange, which is red in acids and yellow in alkali solutions. 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. Redox titration (also called oxidation-reduction titration) is a type of Titration based on a Redox reaction between the Analyte and Titrant Potassium permanganate is the Chemical compound K[[manganese Mn]] O 4 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.

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. Joseph Louis Gay-Lussac (also Louis Joseph Gay-Lussac, December 6, 1778 – May 9, 1850) was a French chemist A pipette (also called a pipet pipettor or chemical dropper is a laboratory instrument used to transport a measured volume of liquid 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. Karl Friedrich Mohr ( November 4, 1806 – September 28, 1879) was a German Pharmacist famous for his early statement of ^[1]

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.

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. Acetic acid, also known as ethanoic acid, is an organic chemical compound, giving Vinegar its sour taste Petrochemistry is the branch of Chemistry that studies the transformation of Crude oil ( Petroleum) and Natural gas into useful products and raw

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. In Mathematics, a coefficient is a Constant multiplicative factor of a certain object

Many titrations require buffering to maintain a certain pH for the reaction. pH is the measure of the acidity or alkalinity of a Solution. Therefore, buffer solutions are added to the reactant solution in the flask. For an individual weak acid or weak base component see Buffering agent.

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). Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state The reaction rate or rate of reaction for a Reactant or product in a particular reaction is intuitively defined as how fast a reaction takes

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. A beaker is a simple container for stirring mixing and heating liquids commonly used in many laboratories An Erlenmeyer flask, commonly known as a conical flask or E-flask, is a widely used type of Laboratory flask which features a conical base and a cylindrical 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 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.

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

A typical titration curve of a diprotic acid, oxalic acid, titrated with a strong base, sodium hydroxide. Oxalic acid is the Chemical compound with the formula H2C2O4 This Dicarboxylic acid is better described with the Sodium hydroxide ( Na[[hydroxide OH]]) also known as Lye, caustic soda and (incorrectly according to IUPAC nomenclature 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). Dependent variables and independent variables refer to values that change in relationship to each other Titration is a common laboratory method of Quantitative chemical analysis that is used to determine the unknown Concentration of a known Reactant Dependent variables and independent variables refer to values that change in relationship to each other 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). Equivalence point or stoichiometric point occurs during a chemical Titration when the amount of Titrant added is equivalent or equal to the amount of 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. In Calculus, a branch of mathematics the derivative is a measurement of how a function changes when the values of its inputs change In Differential calculus, an inflection point, or point of inflection (or inflexion) is a point on a Curve at which the Curvature In Mathematics, a concave function is the negative of a Convex function. The litre or liter (see spelling differences) is a unit of Volume. Sodium hydroxide ( Na[[hydroxide OH]]) also known as Lye, caustic soda and (incorrectly according to IUPAC nomenclature Oxalic acid is the Chemical compound with the formula H2C2O4 This Dicarboxylic acid is better described with the ) 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). Disodium oxalate is a sodium salt of Oxalic acid with the molecular formula Na2C2O4 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.

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. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are Therefore, the Henderson-Hasselbalch equation can be solved in this manner:

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)

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. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are 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). Phosphoric acid, also known as orthophosphoric acid or phosphoric(V acid, is a mineral (inorganic acid having the Chemical formula

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. An acid-base Titration is a method in Chemistry that allows quantitative analysis of the concentration of an unknown Acid or base 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. Redox titration (also called oxidation-reduction titration) is a type of Titration based on a Redox 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. Complexometric titration (sometimes chelatometry) is a form of Volumetric analysis in which the formation of a colored complex is used to indicate the end point The term complex in Chemistry is usually used to describe molecules or ensembles formed by the combination of Ligands and metal Ions. The chelating agent EDTA is very commonly used to titrate metal ions in solution. Chelation is the binding or complexation of a bi- or multidentate Ligand. EDTA is a widely used abbreviation for the Chemical compound ethylenediaminetetraacetic acid (and many other names see table These titrations generally require specialized indicators that form weaker complexes with the analyte. A complexometric indicator is an ionochromic Dye that undergoes a definite color change in presence of specific metal Ions It forms a weak complex A common example is Eriochrome Black T for the titration of calcium and magnesium ions. Eriochrome Black T is a Complexometric indicator that is part of the Complexometric titrations eg Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24
• A form of titration can also be used to determine the concentration of a virus or bacterium. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have 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. A titer (or titre) is a measure of concentration Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure In Toxicology, the median lethal dose, LD50 (abbreviation for “Lethal Dose 50%” or LCt50 (Lethal Concentration & Time of a A plaque-forming unit ( PFU) is a measure of the number of particles capable of forming plaques per unit volume such as Virus particles This procedure is more commonly known as an assay. An assay is a procedure where a property or concentration of an Analyte is measured

Measuring the endpoint of a titration

Main article: Endpoint (chemistry)

Different methods to determine the endpoint include:

• pH indicator: This is a substance that changes colour in response to a chemical change. Equivalence point or stoichiometric point occurs during a chemical Titration when the amount of Titrant added is equivalent or equal to the amount of A pH indicator is a halochromic chemical compound that is added in small amounts to a Solution so that the PH ( Acidity or An acid-base indicator (e. g. , phenolphthalein) changes colour depending on the pH. Phenolphthalein is a Chemical compound with the formula C 20 H 14 O 4 (often written as " HIn pH is the measure of the acidity or alkalinity of a Solution. Redox indicators are also frequently used. A redox indicator (also called an oxidation-reduction indicator) is an Indicator that undergoes a definite color change at a specific Electrode potential 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. A potentiometer is a three-terminal Resistor with a sliding contact that forms an adjustable Voltage divider. This is an instrument that measures the electrode potential of the solution. In Electrochemistry, the standard electrode potential, abbreviated Eo E0 or EO (with a superscript Plimsoll character pronounced 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. A pH meter is an electronic instrument used to measure the PH ( Acidity or alkalinity) of a liquid (though special probes are sometimes used to measure (This is an example of an ion-selective electrode. An Ion-selective electrode (ISE (also known as a specific ion electrode (SIEis a transducer ( Sensor) which converts the activity of a specific Ion dissolved 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. Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an Electric current. 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). Electrophoresis is the most well-known electrokinetic phenomenon. The ionic strength, I, of a solution is a function of the Concentration of all Ions present in a Solution. 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. Precipitation is the formation of a Solid in a Solution during a Chemical reaction. 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. A calorimeter is a device used for Calorimetry, the Science of measuring the heat of Chemical reactions or Physical changes as well as Heat This is important in biochemical titrations, such as the determination of how substrates bind to enzymes. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins
• Thermometric titrimetry is an extraordinarily versatile technique. Thermometric titration is one of a number of instrumental Titration techniques where endpoints can be located accurately and precisely without a subjective interpretation 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. Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. 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). Amperometric titration refers to a class of Titrations in which the Equivalence point is determined through measurement of the Electric current produced 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. )

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. 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 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.

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. Biodiesel refers to a non-petroleum-based Diesel fuel consisting of short chain Alkyl ( Methyl or ethyl) Esters made by In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and pH is the measure of the acidity or alkalinity of a Solution. 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. Petrochemicals are chemical products made from raw materials of Petroleum or other 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. 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. In Chemistry, acid value (or "neutralization number" or "acid number" or "acidity" is the mass of Potassium hydroxide (KOH in In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which See also: pH of fatty acids. In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which
  • Iodine number: a redox titration with colour indication, which indicates the amount of unsaturated fatty acids. The iodine value (or "iodine adsorption value" or "iodine number" or "iodine index" in Chemistry is the mass of Iodine in grams that In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which
  • 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. Saponification value (or "saponification number" also referred to as "sap" in short represents the number of milligrams of Potassium hydroxide or

References

External links

• 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