Eight precipitation jingles in junior middle school chemistry

Potassium, sodium, ammonia and nitrate in the eight precipitation jingles of junior middle school chemistry must be completely dissolved, but silver in chloride is not. Nitrate removes barium and lead, while carbon and phosphorus only dissolve potassium, sodium and ammonia.

Potassium salt, sodium salt, nitrate salt and ammonium salt are all soluble in water, sodium hydroxide, potassium hydroxide, barium hydroxide and ammonia monohydrate are soluble in water, calcium hydroxide is slightly soluble in other alkali, calcium sulfate is slightly soluble in water, silver carbonate and magnesium carbonate are slightly soluble in carbonate, but insoluble in water except potassium, sodium and ammonia, and barium sulfate and silver chloride are neither soluble in acid nor water.

Chemical precipitation method is a kind of water treatment method, which is to add chemicals to the water to convert the dissolved substances that need to be removed from the water into insoluble substances and precipitate them. Used for water treatment to remove calcium, magnesium, iron and manganese. Organic phosphorus in wastewater is transformed into phosphate after biological treatment, and water with high calcium and magnesium content is called hard water. Reducing the concentration of calcium and magnesium is called softening. Softening of hard water can be achieved by chemical precipitation.

Precipitation purpose:

Iron and manganese salts in water can be oxidized by air or other oxidants into insoluble hydroxides or oxides, and then precipitated from water. Hydroxides of metal ions (such as mercury, cadmium, chromium, lead, copper and zinc) harmful to health in wastewater are insoluble or slightly soluble substances. By raising the pH value of wastewater with lime, they can be separated from water.

Chromate ion (CroΥ υ) in wastewater is usually reduced to trivalent chromium ion first, and then precipitated with lime; Barium salt can also be added to make it become barium chromate precipitate with extremely low solubility. After biological treatment, the organic phosphorus in wastewater will be transformed into phosphate, which will make the water body receiving wastewater eutrophic. It can be converted into insoluble aluminum phosphate or iron phosphate by aluminum salt or iron salt and precipitated from water.