Titration

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Titration , also known as titrimetry , is a general laboratory method of quantitative chemical analysis used to determine the concentrations of the analyte identified. Since volume measurements play a key role in the titration, it is also known as volumetric analysis . A reagent, called titran or titrator is prepared as a standard solution. The concentration and volume of the titrant are known to react with a solution of analte or titrand to determine the concentration. The volume of titrant reacting is called the volume of titration .

Video Titration

History and etymology

The word "titration" descends from the French word tiltre (1543), which means "the proportion of gold or silver in a coin or in gold or silver work"; ie, the size of refinement or purity. Tiltre becomes titre , which then means "golden alloyness", and then "concentration of the substance in the given sample". In 1828, French chemist Gay-Lussac first used titre as a verb ( titrer ), meaning "to determine the concentration of the substance in a given sample".

Volumetric analysis originated in the late 18th century in France. FranÃÆ'§ois-Antoine-Henri Descroizilles (fr) developed the first burette (similar to a storied cylinder) in 1791. Joseph Louis Gay-Lussac developed a version of a burette repair that included a side arm, and coined the term "pipette" and "burette" in a paper year 1824 on the standardization of indigo solutions. The first original burette was discovered in 1845 by the French chemist ÃÆ' â € ° tienne Ossian Henry (1798-1873). A major breakthrough in the methodology and popularization of volumetric analysis is that Karl Friedrich Mohr, who redesigned the burette into a simple and comfortable form, and who wrote the first book on the topic, Textbook of analytical chemical titration method ), published in 1855.

Maps Titration

Procedures

Typical titration begins with a glass or Erlenmeyer flask containing a very precise analytical volume and a small number of indicators (such as phenolphthalein) are placed under a calibrated burette or a tincture-containing needle pipette. A small volume of titrant is then added to the analyte and indicator until the indicator changes color as a reaction to the titration saturation angle, reflecting the arrival at the end point of the titration. Depending on the desired endpoint, one drop or less of one drop of titrant can make the difference between permanent and temporary changes in the indicator. When the end point of the reaction is reached, the volume of reactants consumed is measured and used to calculate the concentration of the analyte by

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{                      C                            Â                           =                                  Â                                  C        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                                  t        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â    Â                                  V        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                                  t        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â                              M        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                      Â                              V        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                                  a        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,          Â                                {\ displaystyle \ mathbf {C} _ {a} = {\ frac {\ mathbf {C} _ {t} \ mathbf {V} _ {t } \ mathbf {M}} {\ mathbf {V} _ {a}}}}  Â}

where C _a is the concentration of the analyte, usually in molarity; C _t is the concentration of titer, usually in molarity; V _t is the volume of titrant used, usually in liters; M is the ratio of analytical and reactant mol of balanced chemical equations; and V _a is the volume of the analyte used, usually in liters.

Preparatory Techniques

Typical titration requires titrant and analyte to be in liquid form (solution). Although solids are usually dissolved into an aqueous solution, other solvents such as glacial acetic acid or ethanol are used for special purposes (as in petrochemicals). Concentrate analyzers are often diluted to improve accuracy.

Many non-acid-base titrations require constant pH during reaction. Therefore, the buffer solution may be added to the titration chamber to maintain the pH.

In the example where two reactants in the sample can react with the titrant and only one desired analytes, a separate masking solution may be added to the reaction chamber that covers the unwanted ions.

Some redox reactions may require heating solution solutions and titrations while the solution is still hot to increase the reaction rate. For example, oxidation of some oxalic solutions requires heating to 60 ° C (140 ° F) to maintain a reasonable reaction rate.

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Titration curve

The titration curve is the curve in the plane that is x -the coordinate is the volume of titrant added since the beginning of the titration, and the y -the coordinate is the concentration of the analyte at the appropriate stage of the titration (in acid-base titration, y -the coordinates are usually the pH of the solution).

In acid-base titration, the titration curve reflects the corresponding acid and base strength. For strong acids and strong bases, the curve will be relatively smooth and very steep near the equivalence point. Therefore, small changes in the titrant volume near the equivalence point result in large pH changes and many indicators will be appropriate (eg litmus, phenolphthalein or bromothymol blue).

If one reagent is a weak or basic acid and the other is a strong acid or base, the titration curve is irregular and the pH shifts less with the addition of a bit of titrant near the equivalence point. For example, the titration curve for titration between oxalic acid (weak acid) and sodium hydroxide (strong base) is illustrated. The equivalent point occurs between pH 8-10, indicating the solution is the basis at the equivalence point and an indicator such as phenolphthalein will be appropriate. Titration curves associated with weak bases and strong acids behave similarly, with acidic solutions at equivalence points and indicators such as methyl orange and bromothymol blue to be most appropriate.

Titration between weak acid and weak base has a very irregular titration curve. Therefore, no exact indicator is appropriate and pH measurements are often used to monitor reactions.

The type of function that can be used to describe a curve is called a sigmoid function.

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Titration type

There are many types of titration with different procedures and purposes. The most common types of tititative titration are acid-base titration and redox titration.

Acid base titration

Acid-base titrations depend on neutralization between acids and bases when mixed in solution. In addition to the sample, an appropriate pH indicator is added to the titration chamber, which reflects the pH range of the equivalence point. The acid-base indicator shows the endpoint of the titration by changing the color. The end point and the equivalence point are not exactly the same because the equivalence point is determined by the reaction stoichiometry while the end point is only the color change of the indicator. Thus, careful selection of indicators will reduce indicator error. For example, if the equivalence point is at pH 8.4, the Fenolphthalein indicator will be used instead of Yellow Alizarin because phenolphthalein will reduce the indicator error. Common indicators, their colors, and the pH range in which they change the colors are given in the above table. When more precise results are required, or when the reagent is a weak acid and a weak base, pH meters or conductance meters are used.

For very strong bases, such as organolitium reagents, metal amides, and hydrides, water is generally not a suitable solvent and the indicator that pKa is in the range of aqueous pH changes is not widely used. Instead, the titrant and indicator used are much weaker acids, and anhydrous solvents such as THF are used.

Dalam persamaan, ${\ displaystyle n _ {{ce {A}}}} Â$ dan ${\ displaystyle n _ {{ce {B}}}}$ adalah mol asam ( HA ) dan garam ( XA di Xa adalah kation hand), masing -masing, digunakan dalam buffer, give volume larutan adalah V . Hukum aksi massa diterapkan pada ionisasi air dan disosiasi asam untuk menurunkan persamaan pertama dan kedua. Neraca massa digunakan dalam persamaan ketiga, di mana jumlah ${\ displaystyle V [{\ ce {HA}}]} Â$ dan ${\ displaystyle V [{\ ce {A -}}]} Â Â$ harus sama dengan jumlah mol asam dan basa terlarut, masing-masing. Keseimbangan muatan digunakan dalam persamaan keempat, di mana sisi kiri mewakili muatan total kation dan sisi kanan mewakili total muatan anion: ${\ displaystyle {\ frac {n _ {{\ ce {B}}}} {V}}} Â$ adalah molaritas kation (misalnya natrium, jika garam natrium dari asam atau natrium hidroksida digunakan dalam pembuatan buffer).

Titrasi redoks

Redox titration is based on the oxidation-reduction reaction between the oxidizing agent and the reducing agent. A potentiometer or redox indicator is usually used to determine the endpoint of the titration, such as when one of the constituents is the oxidizing agent of potassium dichromate. The color change from orange to green solution is uncertain, therefore indicators such as diphenylamine sodium are used. Analysis of wine for sulfur dioxide requires iodine as an oxidizing agent. In this case, starch is used as an indicator; complex blue-iodine starch formed in the presence of excess iodine, signaling the end point.

Some redox titration does not require an indicator, because of the strong color of the constituents. For example, in a slight pink coloration indicates the end point of the titration due to the excessive oxidation agent of potassium permanganate. In iodometry, at considerable concentrations, the loss of the dark-brown triiodide ion itself can be used as an endpoint, although at lower concentration sensitivity enhanced by adding starch indicator, which forms a very blue complex with triiodide.

Gas phase titration

Gas phase titration is the titration carried out in the gas phase, particularly as a method for determining reactive species by reaction with the excess of several other gases, acting as a titrant. In a common gas phase titration, the ozone gas is titrated with nitrogen oxide according to the reaction

O ₃ NO -> O ₂ NO ₂ .

After the reaction is complete, the titrant and the remaining product are quantified (for example, by FT-IR); this is used to determine the number of analyte in the original sample.

Gas phase titration has several advantages over simple spectrophotometry. First, the measurement does not depend on the length of the track, since the same length of track is used for the measurement of excess titrations and products. Second, the measurement is independent of linear changes in absorbance as a function of analytical concentration as defined by Beer-Lambert's law. Third, it is useful for samples containing species that disturb the wavelengths normally used for analytes.

Complexometric titration

The titration of complexes depends on the formation of complexes between the analyte and the titrant. In general, they require special complexity indicators that form weak complexes with the analyte. The most common example is the use of starch indicators to improve the sensitivity of iodometric titration, dark blue starch complexes with iodine and iodide become more visible than iodine alone. Other complexity indicators are Eriochrome Black T for the titration of calcium and magnesium ions, and EDTA chelating agents are used to titrate metal ions in solution.

Potential Titration Zeta

Zeta potential titration is a titration in which the solution is monitored by zeta potential, not by indicator, to characterize heterogeneous systems, such as colloids. One of its uses is to determine the iso-electric point when the surface charge becomes zero, achieved by changing pH or adding surfactant. Another use is to determine the optimal dose for flocculation or stabilization.

Assay

Test is a form of biological titration used to determine the concentration of virus or bacteria. Serial dilutions were performed on the sample in a fixed ratio (such as 1: 1, 1: 2, 1: 4, 1: 8, etc.) Until the last dilution did not give a positive test for the presence of the virus. Positive or negative values ​​can be determined by visually examining infected cells under a microscope or by immunoenzymetric methods such as enzyme-linked immunosorbent assay (ELISA). This value is known as the titre.

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Measure the titration endpoint

Different methods for determining end points include:

• Indicators: Substances that change color in response to chemical changes. The acid-base indicator (eg, phenolphthalein) changes color depending on the pH. Redox indicator is also used. A drop of indicator solution is added to the titration at the beginning; the end point has been reached when the color changes.
• Potentiometer: An instrument that measures the electrode potential of a solution. This is used for redox titration; the working electrode potential will suddenly change when the end point is reached.

• pH meter: Potentiometer with electrodes whose potential depends on the number of H ions present in the solution. (This is an example of ion selective electrode). The pH of the solution is measured throughout the titration, more accurately than with the indicator; at the end point there will be abrupt change in the measured pH.
• Conductivity: Measurement of ions in solution. The ion concentration can change significantly in the titration, which changes the conductivity. (For example, during acid-base titrations, H ions and OH ^- react to form H neutral ₂ O.) As the total conductance depends on all ions present in the solution and not all the ions contribute equally (due to mobility and ionic strength), predicting conductivity changes is more difficult than measuring them.
• Color change: In some reactions, the solution changes color without any additional indicators. This is often seen in redox titration when different oxidation states of the product and reactants produce different colors.
• Precipitation: If the reaction produces a solid, the precipitate will form during the titration. The classical example is the reaction between Ag and Cl ^- to form insoluble AgCl salts. Cloudy deposits usually make it difficult to pinpoint the exact ending point. To compensate, settling titration should often be performed as a "back" titration (see below).
• Isothermal titration calorimeters: Instruments that measure the heat generated or consumed by the reaction to determine the end point. Used in biochemical titration, such as determining how the substrate binds to the enzyme.
• Titrimetry Thermometry: Distinguished from calorimetric titrimetry because the heat of reaction (as indicated by temperature or falling rise) is not used to determine the amount of analytes in the sample solution. Conversely, the end point is determined by the rate of temperature change .
• Spectroscopy: Used to measure the absorption of light by the solution during the titration if the reactant, titrant or product spectrum is known. Material concentration can be determined by Beer's Law.
• Amperometry: Measures the current produced by the titration reaction as a result of oxidation or reduction of the analyte. End point detected as change in current. This method is particularly useful when excess titrations can be reduced, as in titration of halides with Ag .

Endpoint and equivalent

Although the equivalent and end points are used interchangeably, they are different terms. Point Equality is a theoretical solution of the reaction: an additional titrant volume in which the number of moles of titrant is equal to the number of analytes, or several multiples (as in polyprotic acid). Endpoint is what is actually measured, the physical changes in the solution as determined by the indicator or instrument mentioned above.

There is little difference between the end point and the titration equivalent point. This error is referred to as an indicator error, and can not be determined.

Back titration

Back titration is an inverted titration; instead of titrating the original samples, the known excess of known standard reagents is added to the solution, and the advantages are titrated. Backtracking is useful if the backtracking endpoints are easier to identify than the endpoint of normal titrations, as in the precipitation reaction. Backtrackation is also useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in an insoluble solid.

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Graphical method

The titration process creates solutions with compositions ranging from pure acids to pure bases. Identifies the pH associated with any stage in a relatively simple titration process for monoprotic acids and bases. The presence of more than one acid or group of bases makes this calculation difficult. Graphical methods, such as equiligraph, have long been used to account for the interplay of combined equilibria. This graphical solution method is easy to implement, but rarely used.

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Custom usage

Acid-base titration

• In biodiesel: waste vegetable oil (WVO) must be neutralized before the batch can be processed. A portion of WVO is titrated on a basis to determine the acidity, so that the rest of the batch can be neutralized appropriately. This removes free fatty acids from WVO that usually react to make soap rather than biodiesel.
• Kjeldahl method: the size of the nitrogen content in the sample. Organic nitrogen is digested into ammonia with sulfuric acid and potassium sulphate. Finally, the ammonia is again titrated with boric acid and then sodium carbonate.
• Acid values: masses in milligrams of potassium hydroxide (KOH) are required to fully titrate the acid in one gram of sample. An example is the determination of free fatty acid levels.
• Saponification value: the mass in milligrams of KOH is required to sap the fatty acids in one gram of sample. Saponification is used to determine the average chain length of fatty acids in fat.
• Esther value (or ester index): calculated index. Esther Value = Saponification value - Acid value.
• The value of the amine: the mass in milligrams KOH is the same as the amine content in one gram of sample.
• The hydroxyl value: the mass in milligrams of KOH corresponding to the hydroxyl group in one gram of sample. The analyzes were assayed using acetic anhydride then titrated with KOH.

Redox titration

• Winkler test for dissolved oxygen: Used to determine the concentration of oxygen in water. The oxygen in the water sample is reduced using manganese (II) sulfate, which reacts with potassium iodide to produce iodine. Iodine is released proportionately with oxygen in the sample, so the oxygen concentration is determined by redox titration of iodine with thiosulfate using kanji indicator.
• Vitamin C: Also known as ascorbic acid, vitamin C is a powerful reducing agent. Its concentration can be easily identified when titrated with Dichlorophenolindophenol blue dye (DCPIP) which becomes colorless when reduced by vitamins.
• Benedictine Reagents: Excess glucose in the urine may indicate diabetes in patients. Benedict method is a conventional method to measure glucose in urine using prepared reagents. In this titration, glucose reduces the copper ions to copper ions which react with potassium thiocyanate to produce white precipitate, indicating the end point.
• The bromine number: The measure of unsaturation in the analyte, expressed in milligrams of bromine absorbed by 100 grams of sample.
• Iodine number: The measure of unsaturation in the analyte, expressed in grams of iodine absorbed by 100 grams of sample.

Miscellaneous

• Karl Fischer's titration: A potentiometric method for analyzing trace amounts of water in a substance. The sample was dissolved in methanol, and titrated with Karl Fischer reagent. The reagents contain iodine, which reacts in proportion to the water. Thus, the water content can be determined by monitoring the potential for iodine excess.

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See also

• The titrations are not watery
• The primary standard is a compound with consistent and reliable properties used to prepare standard solutions for titration.

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References

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External links

• Wikihow: Perform Titration
• An interactive guide for titration
• Science Aid: A simple explanation of titration includes a calculation example
• Freeware titration - simulating pH vs. curve volume, distribution diagram, and real data analysis
• Graphical methods for solving acid-base problems, including titration
• Image and numeric solvers for common acid-base issues - Software Programs for phones and tablets

Source of the article : Wikipedia