Measurement of chloride ions in water
Measurement of chloride ions in water
Chloride ion measurement tests in water can be used to: test the quality of water, which, when high, can damage metal pipes and structures and prevent plant growth.
Operation method
silver nitrate titration
Principle
Silver nitrate titration (also known as Moore's method) is a commonly used method for determining the chlorine content of soluble chlorides. This method is in a neutral or weakly alkaline solution, potassium chromate (K2CrO4) as an indicator, silver nitrate standard solution titration of chloride, due to the solubility of the silver chloride precipitate than silver chromate (Ag2CrO4) precipitate solubility is small, the solution first precipitated white silver chloride precipitate, when the silver chloride precipitation, excess of a drop of AgNO3 solution that is generated with CrO42 - brick red Ag2CrO4 precipitate, indicating that the end point is reached. The main reaction is as follows: Ag++ Cl-= AgCl (white) Ksp = 1.8 x l0-102Ag++ CrO42-= Ag2CrO4(brick red) Ksp= 2.0 x 10-12
Materials and Instruments
Water samples Move I. Instrumentation Caveat 1. Titrations must be carried out in neutral or weakly alkaline solutions with an optimum pH range of 6.5-10. 5. 2. Titrations cannot be performed in acidic solutions. In an acidic medium CrO42-In acidic medium, CrO4 2- is carried out according to the following formula, so that the concentration is greatly reduced, affecting the equal point when the Ag2CrO4precipitation generation at the iso-equivalent point.2 CrO42-+2H+ 2H→ 2 HCrO4→Cr2O72-+2H2O3. This method also cannot be carried out in strongly alkaline solutions because Ag+ 2H 2 Owill form Ag2O precipitate. 4. The amount of indicator used has an effect on how early the end point of the titration is reached.2CrO4concentration is 5 × 10The general concentration of K 2 CrO 4 is 5 × 10-3mol/L is preferred. Common Problems Chloride ( Cl-) is a common inorganic anion in water and wastewater, and it is present in almost all natural water in a highly variable range of levels. In rivers, lakes, and swampy areas, chloride ion levels are generally low, while in seawater, salt lakes, and some groundwater, levels can be as high as tens of grams per liter. If the content of chloride ions in drinking water reaches 250 mg/L, the corresponding cation for sodium ions, you will feel the salty taste; high chloride in the water, it will damage metal pipes and structures, and prevent plant growth. Determination of chlorine methods, including ion chromatography is currently the most common method at home and abroad, simple and fast; silver nitrate titration, mercury nitrate titration using simple instrumentation is suitable for the determination of clean water, but mercury nitrate titration in the use of mercury salts have a high degree of toxicity, is generally not used; potentiometric titration and electrode flow method is suitable for the determination of the color or pollution of the water samples in the monitoring of sources of pollution are more often used. For more product details, please visit Aladdin Scientific website.
Sodium Chloride Reference Reagent
Measuring cylinder Triangular flask Acid burette
1. 100 mL measuring cylinder
2. 250 mL trivets
3. 50 mL acid buretteII. Pharmaceuticals
1. Baseline reagents for sodium chloride
2. Silver nitrate
3. Potassium chromate
4. Aluminum potassium sulphate
5. Ammonia concentrateIII. Reagents
1. Standard solution of sodium chloride (CNaCl=0.0141 mol/L): put the benchmark reagent sodium chloride in a crucible, heat it at 500~600℃ for 40~50 min, cool it down and weigh 8.2400 g by the method of reduction, dissolve it in distilled water, and then dilute it with water to 1,000 mL. 10.0 mL of it is sucked up, and then dilute it with water to 100 mL, and the solution contains 0.500 mg of chloride (Cl-) per milliliter. This solution contains 0.500 mg of chloride (Cl-) per milliliter.
2. Standard solution of silver nitrate ( CAgNO3≈0.014 mol/l L): weigh 2.395 g of silver nitrate, dissolve it in distilled water, and then dilute it with water to 1,000 mL, store it in a brown bottle, and then calibrate its concentration with standard solution of sodium chloride. Calibration of silver nitrate standard solution: suck 25.0 mL of sodium chloride standard solution in a conical flask, add 25 mL of water.Take another conical flask and add 50 mL of distilled water as blank. Add 1 mL of Potassium Chromate Indicator Solution to each flask and titrate with Silver Nitrate Standard Solution under constant shaking until a brick red precipitate just appears.
3. Potassium chromate indicator solution: Weigh 5 g of potassium chromate dissolved in a small amount of water, add drops of the above silver nitrate solution until a red precipitate is generated, shake well, let stand for 12 h, then filter and dilute the filtrate to 100 mL with water.
4. Aluminum hydroxide suspension: dissolve 125 g of potassium aluminum sulfate (KAl( SO4 ) 2-12H20 ) or aluminum ammonium sulfate dodecahydrate in 1,000 mL of water, heat to 60 ℃, under constant stirring, slowly add 55 mL of concentrated ammonia to produce aluminum hydroxide precipitation, stirring thoroughly and then leave for about 1 hour, discard the upper part of the clear night, and then wash the precipitate with water repeatedly, and then wash the precipitate.The precipitate was washed repeatedly with water, and finally until there was no Cl- in the washing solution. After clarification, pour out the supernatant as much as possible, leaving only thick suspension, and finally add 100 mL of water, should be shaken evenly before use.IV. Experimental steps
1. Pre-treatment of water samples
(1) If the water sample is colored, take 150 mL of the water sample, place it in a 250 mL triangular flask, add 2 mL of aluminum hydroxide suspension, shake it well, and then filter it, discarding the first 20 mL.
(2) If the water sample contains sulfites and sulfides, add sodium hydroxide solution to adjust the water sample to neutral or weakly alkaline, then add 1 mL of 30% hydrogen peroxide and mix well.
(3) If the oxygen consumption of the water sample exceeds 15 mg/L, add a few crystals of potassium permanganate, boil and then add a few drops of ethanol to remove the excess potassium permanganate and then filter.
2. Measurement of samples
(1) Take 50 mL of water sample or treated water sample and place it in a conical flask; take another conical flask and add 50 mL of water as blank.
(2) If the pH value of water samples in the range of 6.5 ~ 10.5, can be titrated directly, beyond this range of water samples should be phenolphthalein as an indicator, with 0.05 mol / l of sulfuric acid solution or 0.2% sodium hydroxide solution adjusted to 8.0 or so.
(3) Add 1 mL of potassium chromate solution and titrate with silver nitrate standard solution until a brick red precipitate just appears as the end point. Do the blank titration at the same time.V. Calculation of results
Chloride (Cl-, mg/L) = (V2-V1) x M x 35.45 x 1000/VEq:V1 - Volume of silver nitrate standard solution consumed by distilled water, mL;V2 - volume of silver nitrate standard solution consumed by water sample, mL;M - concentration of silver nitrate standard solution, mol/l;35.45 - molar mass of chloride ion, g/mol.