A question regarding calcium ion analysis in saline solution
Thread Content
Dear experts, I have several questions regarding the testing procedures for analyzing calcium ions in saltwater, and I would appreciate your guidance in answering them. Thank you! Analysis steps: Take 50 mL of the sample and place it in a 250 mL conical flask; add 50 mL of water. If the solution is alkaline, add a few drops of 1+3 hydrochloric acid to make it acidic, then heat it to boiling. After cooling, add 2 mL of 2% hydroxylamine hydrochloride solution and 5 mL of 30% triethanolamine solution, and mix well. Add 5 mL of 2 mol/L sodium hydroxide solution, mix well, then add 0.1 g of calcium indicator. Titrate with 0.005 mol/L EDTA standard solution until the solution changes from wine red to pure blue (the volume used is V1). Question 1: What is the purpose of boiling the sample? Doubt 2: What is the role of adding hydroxylamine hydrochloride? Doubt 3: What is the role of adding triethanolamine?
It’s not necessarily correct. 1. Boil with hydrochloric acid to remove carbonate or bicarbonate ions. 2. Add triethanolamine and hydroxylamine hydrochloride to create a buffer solution, thereby preventing the formation of calcium hydroxide precipitate when sodium hydroxide is added
This post was last edited by qugd on 2020-4-6 at 20:01. Seawater generally contains certain alkaline substances; hydrochloric acid is added to make it acidic, thereby causing the carbonates to decompose and releasing insoluble calcium and magnesium. The addition of hydroxylamine hydrochloride is used to reduce any ferric ions and oxidizing ions that may be present in the sample to lower oxidation states, while triethanolamine helps to chelate and mask these lower oxidation state iron ions as well as heavier metal ions, thereby creating a buffer system. Many high-valent metal ions have a masking effect on indicators. The small amount of strong base added last makes the EDTA-calcium/magnesium formed in the titration system more stable.