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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:
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 net reaction between an aldehyde (or an alpha-hydroxy-ketone) and the copper(II) ions in Benedict's solution may be written as: RCHO + 2 Cu 2+ + 5 OH − → RCOO − + Cu 2 O + 3 H 2 O. The hydroxide ions in the equation forms when sodium carbonate dissolves in water. With the citrate included, the reaction becomes:
Softened water (measured as residual sodium carbonate index) in which calcium and magnesium have been partly replaced by sodium is not suitable for irrigation use, as it tends to cause the development of alkali soils. [28] Non-chemical devices are often used in place of traditional water softening for this application.
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 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.
A spectator ion is an ion that exists both as a reactant and a product in a chemical equation of an aqueous solution. [1] For example, in the reaction of aqueous solutions of sodium carbonate and copper(II) sulfate: 2 Na + + CO 2− 3 (aq) + Cu 2+ (aq) + SO 2− 4 (aq) → 2 Na + (aq) + SO 2− 4 (aq) + CuCO 3
Similarly to its use in baking, sodium bicarbonate is used together with a mild acid such as tartaric acid as the excipient in effervescent tablets: when such a tablet is dropped in a glass of water, the carbonate leaves the reaction medium as carbon dioxide gas (HCO 3 − + H + → H 2 O + CO 2 ↑ or, more precisely, HCO 3 − + H 3 O + → 2 ...