Water is first divided into soft water and hard water according to its own hardness. The hardness of water refers to the content of salts dissolved in the water, that is, the content of calcium and magnesium salts. The unit of hardness is ppm. 1ppm represents the calcium carbonate content of 1 milligram per liter (mg/L) in the water. Water below 142 is called soft water, water above 285ppm is called hard water, and water between 142 and 285 is called moderately hard water.
2. The harm of water hardness:
1. Cause blockage of equipment pipeline
Studies have shown that the scale caused by hard water will cause more than 1/3 of the fuel waste. As the scale accumulates day by day, it will also cause blockage of equipment pipelines, reduced flow, and decreased heating efficiency.
2. Causes excessive metal weight and harms human health
In the scale formed during the use of water heaters and kettles, there are most of calcium carbonate and magnesium carbonate, as well as a variety of heavy metal elements. According to chemical analysis, each gram of scale contains 12 mg of lead, 21 mg of arsenic, 44 mg of mercury, 3.4 mg of cadmium and 24 mg of iron. If it is not frequently removed in time, the harmful elements will dissolve in the water again after repeated boiling and filling. Long-term drinking can cause excessive body weight metal, which is harmful to human health.
3. Detection method:
① EDTA complexometric titration is a commonly used chemical analysis method to determine the hardness of water. It uses chrome black T as an indicator and pH=10 NH3·H2O-NH4Cl (ammonia-ammonium chloride) as a buffer solution under certain conditions. EDTA forms a stable complex with calcium and magnesium ions to determine water The total amount of calcium and magnesium.
①Water hardness kit Test range: 10-200mg/l or 30-600mg/l Specification: 50 times/box
②Soft water hardness kit Test range: 0.4-20mg/l Specification: 50 times/box
② Electrode method: Ion selective electrode is an indicator electrode that is selective for a certain ion. This type of electrode has a special electrode membrane, which has a selective response to specific ions. The relationship between the position of the electrode membrane and the ion content to be measured conforms to the Nernst formula. This method has the characteristics of good selectivity, short balance, simple equipment and convenient operation.