@article{Long_Bảo_Dung_2021, title={Using oxalic acid as a standard for chemical oxygen demand determination with closed reflux–colorimetric method}, volume={130}, url={https://jos.hueuni.edu.vn/index.php/hujos-ns/article/view/6358}, DOI={10.26459/hueunijns.v130i1C.6358}, abstractNote={<p>Potassium hydrogen phthalate (KHP) is used as a standard to determine the chemical oxygen demand (COD) with the closed reflux-colourimetric method (colourimetric method). Besides KHP, it is possible to utilize oxalic acid for this purpose. After boiling at 150 °C for more than 30 minutes in H<sub>2</sub>SO<sub>4</sub> containing Ag<sub>2</sub>SO<sub>4</sub>, K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> reacts completely with H<sub>2</sub>C<sub>2</sub>O<sub>4</sub> at a molar ratio of 1:3. The experimentally determined chemical oxygen demand of H<sub>2</sub>C<sub>2</sub>O<sub>4</sub> coincides with its theoretical value at 16.0 mg O<sub>2</sub>/mole H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>. The average COD values of two river water samples, determined with the colourimetric method by using KHP standard and oxalic acid, are not statistically different. Oxalic acid can be used as a standard to determine COD with the colourimetric method.</p>}, number={1C}, journal={Hue University Journal of Science: Natural Science}, author={Long, Hoàng Thái and Bảo, Nguyễn Sỹ and Dung, Tạ Thị Kim}, year={2021}, month={Jul.}, pages={23-30} }