Titration

The titration ( titrimetry, volumetric or dimensional analysis ) is a method of quantitative analysis in chemistry. A well-known substance whose concentration is unknown ( sample solution) is converted into a specific chemical reaction with a standard solution whose concentration is accurately known. The volume of the standard solution consumed is measured and calculated the unknown concentration of the sample solution on the basis of stoichiometry.

The method is also possible with little equipment and is therefore used early in basic training. Because the results with optimized titration methods are very accurate and the titration can be automated well, it is still widely used in chemical analysis.

In medicine and pharmacology, the dose of a drug by dropping or Abdosierung is under the process of titration dose adjustment understood gradually regulate, until optimal results are achieved ( dose titration, Eng. Dose titration ).

• 5.1 Direct titration
• 5.2 Indirect titration

General Procedure

Using a burette, a reagent of known concentration is added to a sample solution ( Titrand ) ( the standard solution, also titrator, titrant or titrans called ), was added dropwise until the equivalent amount of substance is reached ( also called endpoint or equivalence point ). The endpoint detection can be done with this versatile chemical and physical methods, and also distinguishes the different types of titration. Of the spent volume of the burette can be read. Before starting the titration of the content ( molar concentration c in [mol / l ]) of the standard solution is accurately determined and a correction factor, called the titer determined in order to increase the accuracy of the measurement.

Reaction types

Titrations can be distinguished according to the type of chemical reaction.

Acid -base titration

In the titration, it comes to the acid -base reaction. The endpoint detection can be accomplished by addition of pH - indicators and a color change. It is also possible to measure the pH with electrodes and to determine the end point of application of the pH and of spent acid solution.

Precipitation titration

It will be used to determine precipitation reactions. The reaction of silver ions Ag with chloride ions, Cl - ( Argentometric ) show the end point, sometimes by aggregation of the milky precipitate of (methods for Gay Lussac and Liebig ), sometimes aided by the addition of a dye such as eosin or fluorescein ( titration Fajans ) or by the formation a colored product as Eisenrhodanid ( by titration according to Volhard ) or silver chromate ( titration according to Mohr ). A special case is the hydrolytic precipitation titration, in which is titrated with an alkali salt of a weak acid. An example of this is the determination of total hardness with Kaliumpalmitatlösung in which the Palmitation reacts after crossing the equivalence point with water by hydrolysis to hydroxide ions.

Complexometric determination

The determination is based on complex formation reactions. In this case, dyes may be added, or the color change by forming a complex can be monitored photometrically and thus also determined instrumentally. Widely used is the titration with EDTA.

Redox titration

In some cases, one can take advantage of redox reactions for the determination. Known methods are the Manganometry, Iodatometrie, bromatometry or Cerimetry, each named after titrant used.

Phase transfer

The two - phase titration according to Epton used for the determination of ionic surfactants in aqueous solution. The endpoint is the color change of a dye mixture in the organic- chlorinated phase.

Polyelectrolyte

You used to determine the cationic demand of polyelectrolytes. As titrant is used in anionic suspensions polyDADMAC and cationic Kaliumpolyvinylsulfat.

Evaluation

To evaluate the titration needed to a formula that you usually have to be transformed;

Or

Endpoint detection

• Chemical indicators (visual) Color change of indicators
• Precipitation ( precipitation reactions )

• Potentiometric titration is based on the abrupt change of the electrochemical potential
• Biamperometry
• Conductometric end-point determinations based on measurements of the electrical conductivity
• Thermometric or enthalpic endpoint determinations.

Types of titration

Direct titration

In the direct titration of the sample solution and reagent are reacted with each other directly. The sample solution is introduced and titrated directly with the reagent. In the inverse titration contrast, a measured amount of reagent solution is titrated with the sample solution.

Indirect titration

In indirect titration to be examined substance before the titration in a chemical reaction is implemented. The substance to be measured is converted into a chemical reaction to a precisely defined another substance which is then determined by titration. It is also different in the back titration, in which the sample solution is fully implemented with a specific volume of reagent solution and then the unused portion of the reagent is determined by a titration method, and Substitutionstitration in the product at a given substance initially another substance ( eg replacement cation ) releases ( "substituted" ) which can be back-titrated.

Special titrations

• Amine number
• Bromine number
• Chemical oxygen demand (COD)
• Epton titration
• Ester value ( EZ; quantity of KOH in mg required for the hydrolysis of esters in 1 g fat)
• Halbtitration to determine the acid dissociation constant (pKa ) of an acid
• Iodine value
• Karl Fischer method for determination of water content
• Leitfähigkeitstitration
• Neutralization number (NZ; quantity of KOH in mg required for the neutralization of all the free acids in 1 g of fat)
• Oil demand
• Peroxide value (PV, the amount of bound as peroxide oxygen in meq O2 per kg, which is easily split off as an active oxygen)
• Acid number (AN; quantity of KOH in mg required for the neutralization of the free organic acids in 1 g of fat)
• Saponification
• Anhydrous titration

Automated titration

The different reaction types and types of titration can be implemented in an automated laboratory reactor system. A laboratory automation system recorded with the aid of a suitable probe ( pH glass electrode, conductivity probe, turbidity probe, probe color ... ) the state and controlled by a metering pump, the addition of the reagent solution. The amount is usually determined by automatic measurement of the weight loss of the reagent Vorlagbehälters.

Volumetry without titration

A particularly simple method of volumetry is used for determining the volume of a gas by this displaces a corresponding volume of liquid. Note that the liquid must be chosen to match the gas to be determined. Determination of nitrogen by about azotometer uses this by a potassium hydroxide solution is used as a liquid: this is absorbed in the determination also arising carbon dioxide and water and allows it to read the volume of nitrogen directly on a graduated scale of Azotometerbürette.