Salt is a colorless and transparent cubic crystal with a melting point of 80 1℃, a boiling point of 14 13℃ and a relative density of 2. 165. It has salty taste and is easy to deliquesce with impurities; Soluble in water or glycerol, slightly soluble in ethanol, insoluble in concentrated hydrochloric acid, the aqueous solution is neutral.
form
Salt refers to sea salt, well salt, mineral salt, lake salt and earth salt from different sources. Their main component is sodium chloride, and the state stipulates that the sodium chloride content of well salt and mineral salt shall not be less than 95%. Salt contains barium salt, chloride, magnesium, lead, arsenic, zinc, sulfate and other impurities. We stipulate that the content of barium should not exceed 20 mg/kg. Too much magnesium and calcium in salt will make the salt bitter, and too high fluorine content will also cause poisoning.
Edible salt is iodized salt made by adding a certain amount of iodine agent into refined salt, broken washing salt and sun-dried salt. Iodine in salt can only exert its biological activity in human body after it is converted into iodine ion. Iodide is very unstable in nature, and it is easy to decompose and volatilize and fail. Ordinary edible salt in the market has no shelf life, but the shelf life of edible salt added with trace elements such as iodine, zinc, selenium, calcium and riboflavin is one year.
In industry, salt is dried with seawater, or boiled with well water or salt lake water to precipitate salt crystals. The salt made in this way has many impurities and is called raw salt. Crude salt can be dissolved, precipitated, filtered and evaporated to produce refined salt. In order to eliminate the harm of iodine deficiency and protect citizens' health, the state adopts comprehensive prevention and control measures based on long-term supply of iodized salt.
smell
Strong acid or alkali salt (strong salt) is nonvolatile and odorless. However, weak acid or weak base salt (weak salt) will produce different smells according to the acid-base pair of * * * (for example, acetate will have the taste of acetic acid, and hydrogen cyanide will have the taste of bitter almond, etc. ). In addition, weak acid or weak base salt will volatilize and decompose, and because the hydrolysis reaction and weak salt synthesis reaction are reversible, the decomposition of weak salt will be accelerated in the presence of water.