SäureWert

Säurewert, in chemistry and related fields often referred to as acid value or acid number, is a quantitative measure of acidity in a substance. It expresses how much base, typically potassium hydroxide (KOH), is required to neutralize the acids present in one gram of sample. The result is usually given in milligrams of KOH per gram of sample (mg KOH/g).

The determination is performed by acid-base titration. A sample is dissolved in an appropriate solvent or solvent mixture, and a standardized solution of base (commonly KOH) is added until a defined endpoint is reached, often indicated by a pH indicator such as phenolphthalein. The volume of base used at the endpoint is recorded and used to calculate the Säurewert.

The calculation is typically expressed by the formula:

Säurewert = (V_KOH × N_KOH × 56.1) / m_sample

where V_KOH is the volume of titrant in milliliters, N_KOH the normality of the KOH solution, 56.1 is the molar mass of KOH in g/mol, and m_sample is the mass of the test material in grams. The result is the amount of KOH (in mg) needed per gram of sample.

Applications and interpretation vary by context. In fats and oils, the Säurewert indicates the content of free fatty acids and is used as a quality and spoilage indicator; in fuels, cosmetics, and other chemicals it serves as a general measure of acidic impurities. The method is standardized by organizations such as AOAC and ISO and depends on the sample type, solvent system, and endpoint. Limitations include solvent choice, potential interference from non-volatile acids, and the need for careful endpoint detection.