BS 15491:2021 pdf download – Ethanol as a blending component for petrol — Determination of total acidity — Colour indicator titration method
This document specifies a method for determining the total acidity, calculated as acetic acid, of ethanol to be used in petrol blends. It is applicable to ethanol having total acid contents of between 0,003 % (m/m) and 0,015 % (m/m).
NOTE For the purposes of this document, the terms “% (m/m)” and “% (V/V)” are used to represent the mass fraction and the volume fraction, respectively. WARNING — Use of this document can involve hazardous materials, operations and equipment. This document does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this document to take appropriate measures to ensure the safety and health of personnel prior to the application of the document, and to fulfil statutory and regulatory restrictions for this purpose.
2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN ISO 3170, Petroleum liquids – Manual sampling (ISO 3170)
EN ISO 3696, Water for analytical laboratory use – Specification and test methods (ISO 3696)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at
— IEC Electropedia: available at
total acidity
acidity, calculated as acetic acid, determined by titration and colour indicator as given in this document 4 Principle
A test portion of the ethanol is mixed with an equal volume of neutralized, carbon dioxide free water.
The acid content is titrated with potassium hydroxide solution, to the neutral end point of phenolphthalein. The total acidity is then calculated as acetic acid.
5 Reagents and materials Use only reagents of recognized analytical grade and water complying with the requirements of grade 3 of EN ISO 3696. 5.1 Potassium hydrogen phthalate 5.2 Potassium hydroxide solution 0,01 mol/l, a solution prepared in accordance with
5.2.1 or a commercially available standardized potassium hydroxide solution of equivalent concentration and purity. The reagent shall be protected against carbon dioxide absorption and restandardized frequently enough to detect concentration changes of 0,000 5 mol/l. 5.2.1 Dissolve approximately 0,6 g potassium hydroxide in 1 l of water and standardize using potassium hydrogen phthalate in accordance with 5.2.2.
5.2.2 Dry a quantity of potassium hydrogen phthalate (5.1) in an oven at approximately 120 °C for approximately 2 h. Place in a desiccator and allow to cool. Weigh approximately 0,1 g to the nearest 0,1 mg into a 250 ml flask and record this mass. Add approximately 50 ml of carbon dioxide free water (5.5) and swirl to dissolve. Add 2 drops of phenolphthalein indicator solution (5.3) and using a 50 ml burette (6.5), titrate to neutral end point with the potassium hydroxide solution. Carry out a blank determination using the same volume of carbon dioxide free water (5.5). Calculate the concentration C, in moles per litre, of the potassium hydroxide solution from the formula:
m is the mass, in grams, of potassium hydrogen phthalate;
V 1 is the volume, in millilitres, of potassium hydroxide solution for the titration;
V 0 is the volume, in millilitres, of potassium hydroxide used for the blank.
5.3 Phenolphthalein indicator solution, approximately 10g/l
Weigh approximately 1 g of phenolphthalein into the 100 ml volumetric flask (6.1). Add approximately 20 ml of ethanol (5.4) and swirl until dissolved. Make up to 100 ml with ethanol.
5.4 Ethanol, approximately 95 % (V/V).
5.5 Carbon dioxide free water
NOTE A suitable way of preparing carbon dioxide free water is to place approximately 100 ml of water in a 250 ml conical flask (6.3), fitted with a standard ground glass joint, heated to boiling on either a hot plate or gas burner and boiled for 2 min to 3 min. The flask and its contents are removed from the heat, a soda-lime (5.6) filled guard tube (6.7) is inserted, and cooled to ambient temperature before use.
5.6 Soda lime, for the guard tube (optional).
5.7 Nitrogen, carbon dioxide free.BS 15491 pdf download.