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Hard water usually contains calcium or magnesium ions. Sodium carbonate is used for removing these ions and replacing them with sodium ions. [16] Sodium carbonate is a water-soluble source of carbonate. The calcium and magnesium ions form insoluble solid precipitates upon treatment with carbonate ions:
Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate [9]), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO 3. It is a salt composed of a sodium cation (Na +) and a bicarbonate anion (HCO 3 −). Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder.
The ammonia from reaction (III) is recycled back to the initial brine solution of reaction (I). The sodium bicarbonate (NaHCO 3) precipitate from reaction (I) is then converted to the final product, sodium carbonate (washing soda: Na 2 CO 3), by calcination (160–230 °C), producing water and carbon dioxide as byproducts:
The very pure and finely divided precipitate of calcium carbonate that is generated is a valuable by-product used in the manufacture of toothpaste. The salting-out process used in the manufacture of soaps benefits from the common-ion effect. Soaps are sodium salts of fatty acids. Addition of sodium chloride reduces the solubility of the soap salts.
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
The chloride from the hydrochloric acid in sodium chloride does not hydrolyze, though, so sodium chloride is not basic. The difference between a basic salt and an alkali is that an alkali is the soluble hydroxide compound of an alkali metal or an alkaline earth metal. A basic salt is any salt that hydrolyzes to form a basic solution.
Molten-salt reactors are a type of nuclear reactor that uses molten salt(s) as a coolant or as a solvent in which the fissile material is dissolved. Experimental salts using lithium can be formed that have a melting point of 116 °C while still having a heat capacity of 1.54 J/(g·K).
In the technical terms of physical chemistry, the minimum freezing point of a water-salt mixture is −21.12 °C (−6.02 °F) for 23.31 wt% of salt. Freezing near this concentration is however so slow that the eutectic point of −22.4 °C (−8.3 °F) can be reached with about 25 wt% of salt.