sodium hydroxide

Topics: Sodium hydroxide, Sodium, Base Pages: 9 (2750 words) Published: October 30, 2013
Sodium hydroxide, also known as caustic soda,[2][3] or lye, is an inorganic compound with the chemical formula NaOH (also written as NaHO). It is a white solid, and is a highly caustic metallic base and alkali salt. It is available in pellets, flakes, granules, and as a 50% saturated solution.[citation needed] Sodium hydroxide is soluble in water, ethanol and methanol. This alkali is deliquescent and readily absorbs moisture and carbon dioxide in air. Sodium hydroxide is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 2004 was approximately 60 million tonnes, while demand was 51 million tonnes.[4Physical properties[edit] Pure sodium hydroxide is a whitish solid, sold in pellets, flakes, and granular form, as well as in solution. It is highly soluble in water, with a lower solubility in ethanol and methanol, but is insoluble in ether and other non-polar solvents. Similar to the hydration of sulfuric acid, dissolution of solid sodium hydroxide in water is a highly exothermic reaction in which a large amount of heat is liberated, posing a threat to safety through the possibility of splashing. The resulting solution is usually colourless and odorless with slippery feeling upon contact in common with other alkalis. Chemical properties[edit]

Reaction with acids[edit]
Sodium hydroxide reacts with protic acids to produce water and the corresponding salts. For example, when sodium hydroxide reacts with hydrochloric acid, sodium chloride is formed: NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

In general, such neutralization reactions are represented by one simple net ionic equation: OH−(aq) + H+(aq) → H2O(l)
This type of reaction with a strong acid releases heat, and hence is exothermic. Such acid-base reactions can also be used for titrations. However, sodium hydroxide is not used as a primary standard because it is hygroscopic and absorbs carbon dioxide from air. Reaction with acidic oxides[edit]

Sodium hydroxide also reacts with acidic oxides, such as sulfur dioxide. Such reactions are often used to "scrub" harmful acidic gases (like SO2 and H2S) produced in the burning of coal and thus prevent their release into the atmosphere. For example, 2 NaOH + CO2 → Na2CO3 + H2O

Reaction with amphoteric metals and oxides[edit]
Glass reacts slowly with aqueous sodium hydroxide solutions at ambient temperatures to form soluble silicates. Because of this, glass joints and stopcocks exposed to sodium hydroxide have a tendency to "freeze". Flasks and glass-lined chemical reactors are damaged by long exposure to hot sodium hydroxide, which also frosts the glass. Sodium hydroxide does not attack iron since iron does not have amphoteric properties (i.e., it only dissolves in acid, not base). A few transition metals, however, may react vigorously with sodium hydroxide. In 1986, an aluminium road tanker in the UK was mistakenly used to transport 25% sodium hydroxide solution,[5] causing pressurization of the contents and damage to the tanker. The pressurization was due to the hydrogen gas which is produced in the reaction between sodium hydroxide and aluminium: 2 Al + 2 NaOH + 6 H2O → 2 Na[Al(OH)4] + 3 H2

Precipitant[edit]
Unlike sodium hydroxide, the hydroxides of most transition metals are insoluble, and therefore sodium hydroxide can be used to precipitate transition metal hydroxides. The following colours are observed: Blue-copper, Green-Iron(II), Yellow/Brown-Iron(III). Zinc and Lead salts dissolve in excess sodium hydroxide to give a clear solution of Na2ZnO2 or Na2PbO2. Aluminium hydroxide is used as a gelatinous flocculant to filter out particulate matter in water treatment. Aluminium hydroxide is prepared at the treatment plant from aluminium sulfate by reacting it with sodium hydroxide. Al2(SO4)3 + 6 NaOH → 2 Al(OH)3 + 3 Na2SO4

Saponification[edit]
Sodium hydroxide can be used for the...
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