Ī hot water solution containing 73.1% (mass) of NaOH is a eutectic that solidifies at about 62.63 ☌ as an intimate mix of anhydrous and monohydrate crystals. Even the n = 3.5 hydrate is difficult to crystallize, because the solution supercools so much that other hydrates become more stable. it often decomposes into solid monohydrate and a liquid solution. When heated, the solid dihydrate might melt directly into a solution at 13.35 ☌ however, once the temperature exceeds 12.58 ☌. However, the solution can easily be supercooled down to −15 ☌, at which point it may quickly crystallize as the dihydrate. įor example, when a solution of NaOH and water with 1:2 mole ratio (52.6% NaOH by mass) is cooled, the monohydrate normally starts to crystallize (at about 22 ☌) before the dihydrate. However, solutions of NaOH can be easily supercooled by many degrees, which allows the formation of hydrates (including the metastable ones) from solutions with different concentrations. The other hydrates, except the metastable ones NaOH♳H 2O and NaOH♴H 2O (β) can be crystallized from solutions of the proper composition, as listed above. The only hydrates with stable melting points are NaOH Įarly reports refer to hydrates with n = 0.5 or n = 2/3, but later careful investigations failed to confirm their existence. Tetrahydrate, NaOH♴H 2O, β form: metastable.The known hydrates and the approximate ranges of temperature and concentration (mass percent of NaOH) of their saturated water solutions are: nH 2O, which result in a complex solubility diagram that was described in detail by Spencer Umfreville Pickering in 1893.Sodium hydroxide can form several hydrates NaOH The viscosity of sodium hydroxide solutions plays a direct role in its application as well as its storage. The viscosity of aqueous NaOH, as with any liquid chemical, is inversely related to its service temperature, i.e., its viscosity decreases as temperature increases, and vice versa. s, that is much greater than that of water (1.0 mPa.As with other alkaline solutions, it feels slippery with skin contact due to the process of saponification that occurs between NaOH and natural skin oils.Ĭoncentrated (50%) aqueous solutions of sodium hydroxide have a characteristic viscosity, 78 m Pa The resulting solution is usually colorless and odorless. Similar to the hydration of sulfuric acid, dissolution of solid sodium hydroxide in water is a highly exothermic reaction where a large amount of heat is liberated, posing a threat to safety through the possibility of splashing. Sodium hydroxide is insoluble in ether and other non-polar solvents. It is highly soluble in water, with a lower solubility in polar solvents such as ethanol and methanol. Pure sodium hydroxide is a colorless crystalline solid that melts at 318 ☌ (604 ☏) without decomposition and boils at 1,388 ☌ (2,530 ☏). Worldwide production in 2004 was approximately 60 million tons, while demand was 51 million tons. Sodium hydroxide is used in many industries: in the making of wood pulp and paper, textiles, drinking water, soaps and detergents, and as a drain cleaner. The commercially available "sodium hydroxide" is often this monohydrate, and published data may refer to it instead of the anhydrous compound.Īs one of the simplest hydroxides, sodium hydroxide is frequently used alongside neutral water and acidic hydrochloric acid to demonstrate the pH scale to chemistry students. H 2O crystallizes from water solutions between 12.3 and 61.8 ☌.It is highly soluble in water, and readily absorbs moisture and carbon dioxide from the air. Sodium hydroxide is a highly corrosive base and alkali that decomposes lipids and proteins at ambient temperatures and may cause severe chemical burns. It is a white solid ionic compound consisting of sodium cations Na + and hydroxide anions OH −. Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH.
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