[Chemistry Class Notes] Karl Fischer Titration Pdf for Exam

Karl Fischer titration is defined as a titration method that uses either volumetric or coulometric titration to determine the water quantity present in a given analyte. This method, which is used for quantitative chemical analysis, was developed in 1935 by the German chemist named “Karl Fischer.” Today, the specialized titrators (which are called Karl Fischer titrators) have been made available to carry out such titrations.

Principle of Karl Fischer Titration

Let us look at the Karl Fischer principle in detail.

The principle of Karl Fischer’s titration is completely based on the oxidation reaction between sulphur dioxide and iodine. Water reacts with sulphur dioxide and iodine to form hydrogen iodide and sulphur trioxide. When all the water is consumed, it reaches an endpoint. The chemical equation that takes place for the reaction between sulphur dioxide, iodine, and water (which is employed during the Karl Fischer titration) is given below.

I₂ + SO₂ + H₂O → 2HI + SO₃

Karl Fischer Titration Equipment

• Drying tube,

• Electrode analysis,

• Sample injection cap,

• Drain cook,

• A cathode chamber,

• Rotor,

• Detection electrode,

• KF reagent,

• Anode chamber.

Ingredients of KF Reagent

• Iodine,

• Solvent (methonal),

• Sulphur dioxide,

• Buffer (Imidazole).

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Karl Fischer Titration Procedure

The experiment of Karl Fischer’s titration can be performed in two different methods. They are listed below.

This particular technique is suitable in determining water content down to 1 percent of water. The respective sample is dissolved in KF methanol, and then iodine is added to KF Reagent. Here, the endpoint is detected potentiometrically.

Here, the endpoint is electrochemically detected in this experiment. Iodine needed for the KF reaction is obtained by anodic oxidation of iodide from the solution.

Applications of Karl Fischer Titration

• It can be used in technical products such as plastics, oils, gases,

• It is used in cosmetic products,

• It is used in pharmaceutical products,

• It is used in the industry.

Preparation of the KF Reagent

Prepare a solution by mixing 670 mL of methanol and 170 mL of pyridine. Now, add 125 g of iodine to the solution and cool it. Then, take a 250 mL graduated cylinder and add 100 mL of pyridine to it. Keep the solution in an ice bath. Pass in dry sulphur dioxide till its volume reaches 200 mL.

Advantages and Disadvantages of Karl Fischer Titration

The popularity of Karl Fischer titration (henceforth called KF) is due in large part to many practical advantages that it holds over other moisture determination methods, like speed, accuracy, and selectivity.

KF is selective for water since the titration reaction itself consumes water. In contrast, the mass loss measurement on drying will help to detect the loss of any volatile substance. However, the strong redox chemistry (SO2 or I2) means that the redox-active sample constituents can react with the reagents. Because of this reason, KF is not suitable for solutions containing dimethyl sulfoxide (for example).

KF has high precision and accuracy, typically within 1% of the available water. For example, 3.00% appears as 2.97 – 3.03%. Although this KF is a destructive analysis, the sample quantity is very small and typically limited by the weighing accuracy. For instance, to obtain 1% accuracy using a scale with a typical accuracy of 0.2 mg, the sample solution must contain 20 mg water, which is 200 mg (for example) for a sample with 10% water.

Whereas, for coulometers, the measuring range falls from 1–5 ppm to around 5%. Volumetric KF readily measures the sample solution up to 100%, but it requires impractically large amounts of sample for analytes which are less than 0.05% water. The response of KF is linear, and therefore, single-point calibration using a calibrated 1% water standard becomes sufficient, and there is no need for calibration curves.

KF is suitable to measure the liquids, and also with special equipment, gases. The major disadvantage with solids is: water has to be accessible and brought easily into the methanol solution. Several common substances, especially the foods like chocolate, release water slowly and with difficulty, claiming for additional efforts to bring the total water content reliably into contact with the KF reagents. For example, a high-shear mixer can be installed in the cell to break the sample. KF has problems with strong binding to water compounds, as in the water of hydration. For example, lithium chloride. So, KF is unsuitable for special solvents like LiCl or DMAc.

KF is also suitable for automation. In general, KF is conducted using a separate KF titrator, or for the volumetric titration, a KF titration cell will be installed into a general-purpose titrator.

It is also possible to use the volumetric titration with visual detection of a titration endpoint with the colored samples by UV or VIS spectrophotometric detection.

Karl Fischer Titration – Principle, Procedure, Applications, Preparation, Advantages, and Disadvantages

In 1935 a German researcher Karl Fischer distributed a technique for assurance of water content in examples. This was a titrimetric technique dependent on Bunsen response utilized for assurance of sulfur dioxide in watery arrangements:

SO₂ + I₂ + 2 H₂O → H₂SO₄ + 2 HI

Karl Fischer found that assuming sulfur dioxide is included in the abundance, a similar response can be utilized for water assurance by titration of the delivered acids. His base of the decision was pyridine which was supposedly “simply remain in the rack”. In his honor, the titration is named Karl Fischer titration (KF titration for short).

Before long both unique stoichiometry and reagents were reexamined.

Fischer introduced the response which gave inaccurate molar proportions accepting watery Bunsen response in which methanol works just as a dissolvable.

The mistake was rectified by Smith, Bryant, and Mitchell who found that pyridine acts just like a cradle substance, giving us the response which is utilized today:

H₂O+ I₂ + [RNH]+SO₃CH₃⁻+ 2 RN → [RNH]+SO₄CH₃⁻+ 2 [RNH]⁺I⁻

The titration was directed physically from the beginning. The endpoint was the announced determination of earthy colored tone from the additional overabundance of iodine. This was slow, yet in addition not reasonable for shaded examples.

These days KF titration is robotized and generally utilized for water assurance in different businesses.

Karl Fischer Titration Techniques

There are two unique procedures for water assurance by Karl Fischer: Volumetric KF titration and coulometric KF titration.

Volumetric assurance is appropriate for assurance of water content down to 1% of water. The example is broken down in KF Solvent (ordinarily methanol-based) and the iodine is added as a piece of a KF Reagent containing sulfur dioxide and iodine disintegrated in pyridine and methanol. They are not really set in stone potentiometrically.

Karl Fischer Titration Reagents and Applications

Reagents for Karl Fischer titration are accessible in an expansive reach, contingent upon the reason and natural familiarity with the client. Pyridine can be supplanted with a more grounded base (and less malodorous) imidazole, and ethanol can be utilized rather than methanol as a more “green” solution of dissolvable. Various helpers are accessible, for example, added substances for fats and oils, reagents for assurance of low water substance, solubilizers for inadequately solvent substances, and support answers for firmly antacid or emphatically acidic examples.

Karl Fischer titration is generally utilized for direct investigation of water content in different businesses, as a solid and hearty technique. In the food industry, it is utilized for water content assurance in natural product juices, honey, flour, noodles, chips, cocoa powder, in the oil industry for a wide range of various oils, fuel, lamp oil, and petrol, in surface-level industry for assurance of water in shampoos, creams, lipstick, tooth glue, in the pharmaceutical industry for unrefined components, dynamic substances, lyophilized substrates, tablets, treatments, oils. It is utilized for assurance of water in silk, fleece, wood, paper, and surprisingly in building materials like zeolite and concrete.

The rundown simply continues. This is only the verification that with the ideal decision of strategy and appropriate reagents Karl Fischer titration can be reasonable for water content assurance in practically all possible examples. It is nothing unexpected that this titration is a go-to procedure in any research facility, in any industry.