Definition and Uses :
Pure sodium hydroxide is a colorless, crystalline solid that melts at 318 ° C without decomposition. It is highly soluble in water, with lower solubility in ethanol and methanol, but is insoluble in ether and other nonpolar solvents.
Similar to the hydration of sulfuric acid, dissolving solid sodium hydroxide in water is an extremely exothermic reaction in which a large amount of heat is released, posing a safety hazard due to the possibility of splashing. The resulting solution is usually colorless and odorless. As with other alkaline solutions, it becomes slippery on contact with the skin.
Sodium hydroxide reacts with protic acids to produce water and related salts. For example, when sodium hydroxide reacts with hydrochloric acid, sodium chloride is formed:
NaOH (aq) + HCl (aq) → NaCl (aq) + H 2 O ( l )
In general, such neutralization reactions are represented by a simple net ionic equation:
OH - (aq) + H + (aq) → H 2 O (I)
This type of reaction with a strong acid releases heat and is therefore exothermic. These acid-based 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 the air.
Caustic Soda is a white, hygroscopic substance. It dissolves readily in water and forms a soft, slippery, soapy solution. It is irritating to human tissue. It is used in the laboratory to capture acidic gases such as CO2. It is used in the production of many chemicals in industry, in the artificial silk, soap, paper, paint, detergent industry and in petroleum refining. When it reacts with water, its temperature rises to 50 degrees Celsius in about 5 minutes and remains hot for about 15 minutes.