Analysis of acetic acid

This post was last edited by qugd on 2009-11-4 08:56. Chromatography can be used, as can titration; however, when titration is not used, the accuracy of the sample volume taken directly affects the accuracy of the measurement results. If titration is used, it is recommended to prepare the sample into a solution of a precise and consistent concentration before conducting the measurement. This is a typical titration process of a strong base with a weak acid; the endpoint of the titration is at a weakly basic level. Phenolphthalein can be used as an indicator to determine this endpoint, and standard base can be employed for the titration, which is completely sufficient.

Theoretically, titration can be used, but since the purity of acetic acid is over 99.8%, the allowable error in titration can result in values greater than 100; the final reading from titration has a significant impact on the results when using about 2 grams of acetic acid. Moreover, the consistency of the results obtained through titration is not good, even when the repetitions are accurate. However, the results obtained after titration after a one-day interval vary significantly, being either too high or too low

For constant analysis, the absolute error of titration tests is generally between 0.2-0.5%, so titration is clearly not suitable for determining the main content in highly pure chemicals. Generally, for highly pure substances, it is not necessary to test the main component content; instead, the impurity reduction method is used, that is, the purity percentage = 100 – (total percentage of various impurities). Trace organic components can be analyzed using photometry, liquid and gas chromatography, etc.; inorganic components can be analyzed using emission spectroscopy, atomic absorption, and so on. As far as I know, there are **standards** for high-purity glacial acetic acid; it’s worth taking some time to look into them.

This post was last edited by fengxuemei on 2009-11-5 at 11:24. For GBT 1628-2008 Industrial Glacial Acetic Acid, http://bbs.hcbbs.com/viewthread.php?tid=418259&highlight=GBT%2B1628-2008%2B%B9%A4%D2%B5%D3%C3%B1%F9%D2%D2%CB%E1, the method used is acid-base titration; however, the content of formic acid must be deducted when calculating the results. For specific LZ details, you can refer to GB.

The acid content should still be determined by titration, using CO2-free water, and the sample must not be volatile

We use the titration method, and the analytical error is not too large. The possible reasons for this issue in the original poster’s case are: 1) there are problems with the preparation of the alkaline solution; 2) the content of formic acid has an impact. The current standard method is indeed the titration method

The acetic acid content is determined by titration: approximately 2.5 g of acetic acid is accurately weighed using a weighing flask with a stopper, and placed in an Erlenmeyer flask containing 50 ml of carbon dioxide-free distilled water. Sodium hydroxide with a concentration of 1.0 mol/L is then used for titration, with phenolphthalein as the indicator； The error mainly comes from 1, the accuracy of weighing ； 2. Volatilization of acetic acid ； 3. Calibration accuracy of the burette ； 4. Temperature calibration ； 5. Operator skills. The calculation result is then subtracted by the formic acid conversion value.

The simplest method for determining acetic acid content: the freezing point method (16.4–16.6°C), very accurate!

The error in titration methods is mainly due to the requirement that the content accuracy must be at 99.? ? The actual number of significant figures is 5 (since the first digit is greater than 8, one additional significant figure is added). The reference material used for calibrating sodium hydroxide has a purity level between 99.95% and 100.05%, so its precision is not that high. Therefore, the titration result can only be accurate to four digits. And there is an absolute error of 0.1%. A premium grade is defined as having a value of ≥99.8; an error of 0.1% marks the threshold between the premium grade and the qualified grade. Therefore, we use an indirect calibration method for our sodium hydroxide – by purchasing standard acids with a precision of 0.00001 to determine the concentration of sodium hydroxide. To date, no quality issues have arisen as a result of this approach!

The freezing point method is accurate, but freezing point detectors are expensive; therefore, the titration method is still used by most people