rinciple: In the presence of excess potassium sodium tartrate, titrate the total alkali with hydrochloric acid, then add potassium fluoride, aluminum hydroxide and fluoride ions combine to release hydroxide ions, and then titrate these hydroxide ions with hydrochloric acid, can calculate aluminum The amount of ions.
Al (OH)4- +H++ 4(C4H4O6) 42- →[Al (OH) 3 (C4H4O6) 4]8- + H2O
[Al (OH) 3 (C4H4O6) 4]8- +6F- →AlF63-+3OH -+4 (C4H4O6) 42-
OH- +H+ →H2O
Step: Accurately absorb 5 mL of alkaline etchant in a 250 mL Erlenmeyer flask, add 30 mL of sodium potassium tartrate solution and 50 mL of distilled water, add 2 drops of phenolphthalein indicator, and titrate with hydrochloric acid standard solution (concentration is c(HCl)) When the red color disappears to the end point, record the titration reading as V1; then add 20 mL of potassium fluoride solution (the solution is red again), continue to titrate with hydrochloric acid standard solution until the red color disappears to the end point, and record the titration reading as V2.
Total base c (OH) , g / L = 40 c ( HCl ) V1/ 5.00
Aluminum c (Al) , g / L = 27 c ( HCl ) V2 / (3 × 5. 00)
Free base c (OH) , g / L = 40 c ( HCl) ( V1-V2) / 5.00