... , then aqua. crimson or brown), use 0.1N sodium thiosulfate to titrate to yellowish, add several drops of ... add 20 ml 10% sodium hydroxide solution, place a solution, starch solution 1 %. Reagents: Sodium hydroxide 10 %, H2O2 30 %, hydrochloric acid ... conc., potassium iodide, 0.1 N sodium thiosulfate Analysis by Titration ...