Preparation of reagents for purified water testing

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1% Diphenylamine sulfuric acid solution: Weigh 0.1 g of diphenylamine and add it to 100 ml of concentrated sulfuric acid; dissolve it, then store the solution in a sealed container. Since concentrated sulfuric acid is hygroscopic, it absorbs water vapor from the air, causing the 1% diphenylamine sulfuric acid solution to turn blue. If you want to conduct a nitrate test, you must prepare this solution anew; otherwise, it will be difficult to observe the color change. Therefore, it is necessary to store the solution in a sealed container. Calcium hydroxide solution: Take 3 g of calcium hydroxide, place it in a glass bottle, add 1000 ml of water, seal the bottle tightly, shake it vigorously from time to time, and let it stand for 1 hour to obtain the solution. Pour off the clear liquid from the top after some time. ) C Potassium mercuric iodide base: Take 10 g of potassium iodide and dissolve it in 10 ml of water; then slowly add a saturated aqueous solution of mercuric dichloride, stirring continuously until a red precipitate forms that no longer dissolves. After adding 30 g of potassium hydroxide and dissolving it, the solution should immediately turn yellow. Silver nitrate: Take 1.75 g of silver nitrate and dilute it to 100 ml using distilled water that has been freshly boiled and then cooled to room temperature. Barium chloride: Weigh 5 g of barium chloride and add distilled water that has just been boiled and then cooled to a volume of 100 ml, thereby obtaining the solution. Ammonium oxalate: Weigh 3.5 g of ammonium oxalate, then add distilled water that has been freshly boiled and cooled to a volume of 100 ml to obtain the solution. 0.02 mol/L potassium permanganate solution: Weigh 0.32 g of potassium permanganate, add distilled water that has been freshly boiled and then cooled to a volume of 100 ml, bring the mixture to a boil for 15 minutes, seal it tightly, let it stand for more than 2 days, and then shake well to obtain the solution. 2 mol/L sulfuric acid solution: Measure 6 ml of concentrated sulfuric acid, slowly add an appropriate amount of distilled water, and dilute to 100 ml to obtain the solution. p-Aminobenzenesulfonamide: Take 1.0 g of p-aminobenzenesulfonamide, dissolve it in an appropriate amount of dilute hydrochloric acid, and dilute to 100 mL to obtain the solution. Naphthyl ethylenediamine hydrochloride: Take 0.1 g and dissolve it in an appropriate amount of pure water, then dilute to 100 mL to obtain the solution. Nitrite standard solution: Precisely weigh 0.750 g of sodium nitrite, dissolve it in water, and dilute to 100 ml. Shake well. Then, accurately measure 1 ml of this solution and dilute it with water to 100 ml again, shaking well. After that, accurately measure another 1 ml and dilute it with water to 50 ml, shaking well. This gives the desired solution (each 1 ml corresponds to 1 ug of NO2). Standard nitrate solution: Take 0.163 g of potassium nitrate, dissolve it in water and dilute to 100 ml; shake well. Then, accurately measure 1 ml of this solution, dilute it in water to 100 ml, and once again accurately measure 10 ml of that solution, diluting it in water to 100 ml after shaking. This gives the desired solution (each 1 ml corresponds to 1 μg of NO3). 3. Water free of nitrates, nitrites, and ammonia: Take 1000 ml of purified water, add 1 ml of dilute sulfuric acid and 1 ml of potassium permanganate solution (0.02 mol/L), then distill to obtain the desired water.