Acid value


Acid value

In chemistry, acid value (or "neutralization number" or "acid number" or "acidity") is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance. The acid number is a measure of the amount of carboxylic acid groups in a chemical compound, such as a fatty acid, or in a mixture of compounds. In a typical procedure, a known amount of sample dissolved in organic solvent (often isopropanol), is titrated with a solution of potassium hydroxide with known concentration and with phenolphthalein as a color indicator.

The acid number is used to quantify the amount of acid present, for example in a sample of biodiesel. It is the quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize the acidic constituents in 1 g of sample.

AN=(V_{eq}-b_{eq})N\frac{56.1}{W_{oil}}

Veq is the amount of titrant (ml) consumed by the crude oil sample and 1ml spiking solution at the equivalent point, beq is the amount of titrant (ml) consumed by 1 ml spiking solution at the equivalent point, and 56.1 is the molecular weight of KOH. WOil is the weight of the sample in grams.

The molarity concentration of titrant (N) is calculated as such:

N=\frac{1000W_{KHP}}{204.23V_{eq}}

In which WKHP is the amount (g) of KHP in 50 ml of KHP standard solution, Veq is the amount of titrant (ml) consumed by 50 ml KHP standard solution at the equivalent point, and 204.23 is the molecular weight of KHP.

There are standard methods for determining the acid number, such as ASTM D 974 and DIN 51558 (for mineral oils, biodiesel), or specifically for Biodiesel using the European Standard EN 14104 and ASTM D664 are both widely utilised worldwide. Acid number (mg KOH/g oil) for biodiesel should to be lower than 0.50 mg KOH/g in both EN 14214 and ASTM D6751 standard fuels. This is since the FFA produced may corrode automotive parts and these limits protect vehicle engines and fuel tanks.

As oil-fats rancidify, triglycerides are converted into fatty acids and glycerol, causing an increase in acid number. A similar observation is observed with Biodiesel aging through analogous oxidation processes and when subjected to prolonged high temperatures (ester thermolysis) or through exposure to acids or bases (acid/base ester hydrolysis).

See also


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Look at other dictionaries:

  • acid value — noun (chemistry) the amount of free acid present in fat as measured by the milligrams of potassium hydroxide needed to neutralize it as the glycerides in fat slowly decompose the acid value increases • Topics: ↑chemistry, ↑chemical science •… …   Useful english dictionary

  • acid value — rūgščių skaičius statusas T sritis Standartizacija ir metrologija apibrėžtis KOH kiekis (mg), kurio reikia laisvosioms rūgštims, esančioms 1 g medžiagos, neutralizuoti. atitikmenys: angl. acid number; acid value vok. Neutralisationszahl, f;… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • acid value — rūgščių skaičius statusas T sritis Standartizacija ir metrologija apibrėžtis Šarmo (bazės) kiekis, išreikštas skaičiumi, lygiaverčiu KOH miligramams gramui, reikalingas visų rūgščiųjų sudedamųjų dalių, esančių 1 g bandinio, titravimui, kuris… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • acid value — rūgščių skaičius statusas T sritis chemija apibrėžtis KOH kiekis (mg), kurio reikia laisvosioms rūgštims, esančioms 1 g medžiagos, neutralizuoti. atitikmenys: angl. acid number; acid value rus. кислотное число …   Chemijos terminų aiškinamasis žodynas

  • acid value — Chem. See acid number. * * * …   Universalium

  • acid value — (Chemistry) amount of free acid that exists in fat that is measured by the milligrams of potassium hydroxide which is required to neutralize it …   English contemporary dictionary

  • acid value — /ˈæsəd ˌvælju/ (say asuhd .valyooh) noun the number of milligrams of potassium hydroxide neutralised by the free acids present in one gram of a fat, oil, or resin. Also, acid number …   Australian English dictionary

  • Acid value — Кислотное число; коэффициент кислотности; Кислотное число; Коэффициент кислотности …   Краткий толковый словарь по полиграфии

  • acid value — see under number …   Medical dictionary

  • acid number — n. a number indicating the amount of free acid present in a substance, equal to the number of milligrams of potassium hydroxide needed to neutralize the free fatty acids present in one gram of fat or oil: also called acid value …   English World dictionary


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