ASTM D7795 Standard Test Method for Acidity in Ethanol and Ethanol Blends by Titration
TEST METHOD B - COLOR END POINT TITRATION
13. Apparatus
13.1 Buret, 10-mL, graduated in 0.05-mL subdivisions.
13.2 Erlenmeyer Flask, 250-mL capacity.
13.3 Sparging System, a gas delivery system suitable to deliver inert gas directly into the liquid sample, with an external pressure of 10 psi (69 kPa).
14. Reagents and Materials
14.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is pure enough to be used without lessening the accuracy of the determination.
14.1.1 Commercially available solutions may be used in place of laboratory preparations provided the solutions have been certified as being equivalent.
14.1.2 Alternate volumes of the solutions may be prepared, provided the final solution concentration is equivalent.
14.1.3 Purity of Water - Unless otherwise indicated, reference to water shall be understood to mean reagent water that meets the requirements of either Type II or III of Specification D1193.
14.1.3.1 Prepare CO2 free water by sparging 1 L of water (14.1.3) and with nitrogen (14.1.9) for no less than 3 min.
14.1.4 Potassium Acid Phthalate (KHC8H4O4), primary standard, dried - Place 4 to 5 g of primary standard potassium acid phthalate (KHC8H4O4) of 100-mesh fineness, in a weighing bottle at 120°C for 2 h. Stopper the container and cool it in a desiccator.
14.1.5 Potassium Hydrogen Phthalate (KHP) Solution - For a volumetric standard, weigh approximately 1.0 g of dried KHP and record the weight to the nearest +/- 0.0001 g and transfer it to a 500 mL Class A volumetric flask swept free of carbon dioxide. Add 200 mL of Type II DI water that is free of carbon dioxide, stopper and swirl gently until it is dissolved. Dilute to 500 mL and mix thoroughly. Express the concentration of KHP in solution as Molarity in moles of KHP per liter of solution. The use of a volumetric flask can be avoided by weighing 1.0 g of dried KHP to the nearest 0.0001 g into a beaker and adding 500 g of Type II carbon dioxide free DI water. Record the total mass of water and KHP to the nearest +/- 0.01 g and express the concentration of KHP in the solution as mg KHP per gram of solution. Mix thoroughly to dissolve the KHP and store it in a closed container.
14.1.6 Sodium Hydroxide, Standard Solution (0.01 N) - Prepare and standardize a 0.01 N sodium hydroxide (NaOH) solution (note 3) in accordance with the Preparation and Standardization of Solutions, Precision and Bias, Preparation of 50 % of NaOH Solutions and standardizations section of Practice E200.
NOTE 2 - Alternatively, KOH (0.01 N) in isopropyl alcohol solution may be used instead of (0.01 N) NaOH.
14.1.7 Alcohols, refined, ethyl or isopropyl.
NOTE 3 - Isopropyl alcohol (99 % grade) conforming to Specification D770, or 190 proof ethyl alcohol conforming to formula No. 3A of the U.S, Bureau of Alcohol, Tobacco, and Firearms as defined in Title 27, Code of Federal Regulations (or equivalent regulations in other jurisdictions) is suitable for use as the solvent. The use of methyl alcohol is not recommended.
14.1.8 Phenolphthalein Indicator Solution, (10 g/l) - Dissolve 1 g of phenolphthalein in ethyl or isopropyl alcohol and dilute to 100 mL with alcohol.
14.1.9 Nitrogen, 99.9 % pure.
15. Standardization
15.1 Standardization of the 0.01 mol/L (M) NaOH Titrant:
15.1.1 Weigh 2 g of the KHP solution and record the mass to the nearest 0.0001 g (or pipet 2 mL of KHP solution using a Class A pipet) into a beaker and add 50 6 5 mL of CO 2 free water. Place vessel on the magnetic stirrer and titrate the KHP standard with the 0.01 mol/L (M) NaOH. Record the volume of titrant used to neutralize the KHP using phenolphthalein as end point. This volume of KHP solution may use approximately 2 mL of the 0.01 M NaOH.
15.1.2 Prepare two additional KHP solutions and standardize the titrant as above in 15.1.1.
15.1.3 Use the three determinations to calculate the average concentration (molarity) of the NaOH. The average of the titrant molarity determinations shall agree within +/- 0.0005 mol/L (M). Use this average to calculate the acidity of the titrant (see 13.1).
16. Procedure - Color End Point Titration
16.1 Weigh 60 +/- 5 g to the nearest 0.001 g of Ethanol or Ethanol blend into a titration beaker and record the mass.
16.2 Add 1 mL of Phenolphthalein Indicator Solution.
16.3 Sparge the sample with nitrogen at a flow rate of 200 +/- 20 mL/min for 60 s prior to titration, and continue to sparge throughout the entire analysis.
16.4 Record the volume of titrant used to reach the first stable pink color, which lasts at least 15 s.
