Copper content determination

For ammonium bifluoride, refer to the analysis methods for crude copper or copper concentrate… I found a method for analyzing brass; the procedure is more or less the same, with pure copper being used to calibrate sodium thiosulfate! Weigh 3.0000 g of the sample and place it in a 500 ml Erlenmeyer flask. Slowly add 50 ml of nitric acid, then cover the flask with a watch glass. Once the intense reaction has ceased, place the flask on an electric heating plate at a low temperature to heat it until the substance is completely dissolved. Remove the flask from the heat source, wash the Erlenmeyer flask and its walls with water, and allow everything to cool to room temperature. Transfer the solution to a 500 ml volumetric flask (Class A); if there are residues, filter them. Wash the beaker with water, and add the washings to the volumetric flask. Dilute to the mark with distilled water. Accurately transfer 50.0 ml of the aforementioned sample solution into a 500 ml Erlenmeyer flask, add 2 ml of bromine-saturated solution, and place it on an electric hot plate at a low temperature to evaporate the solution until its volume is approximately 1 ml. Remove it from the heat, allow it to cool slightly, then add 30 ml of water to rinse the walls of the flask. After cooling to room temperature, neutralize the solution with ammonia until copper hydroxide precipitates forms. Add 3 ml of glacial acetic acid and 1 ml of ammonium fluoride-saturated solution; rinse the walls of the flask with water, mix well, and add about 4 g of potassium iodide. Immediately titrate with a sodium thiosulfate standard solution with a concentration of C(Na2S2O3•5H2O) = 0.1 mol/L. When the solution turns pale yellow, add 5 ml of starch solution (0.5%) and continue titrating until the solution becomes pale blue. Then add 5 ml of potassium thiocyanate solution (200 g/L), shake the mixture, and wait for the adsorbed iodine to be released; continue titrating until the pale blue color disappears, indicating the end of the titration.

The key is to remove the effect of nitrite. Sulfuric acid can be added to produce smoke, then it is cooled, water and urea are added, and the mixture is boiled for 5 minutes.