Caustic soda is the common name for sodium hydroxide. It is one of the strongest known alkali (water-soluble base). The chemical formula of caustic soda is NaOH. It is a white solid comprising sodium cations (Na+) and hydroxide anions (OH–).
Caustic soda is highly alkaline and it can deform protein structures and burn chemicals. The enthalpy of its hydrolysis reaction is exothermic because of which, it has hygroscopic properties. It is usually used to absorb moisture and carbon dioxide during the combustion analysis of organic compounds.
Caustic soda has a variety of uses due to its corrosive nature. It has a wide range of common uses and industrial applications to produce several chemical compounds.
Common uses of caustic soda
Caustic soda is commonly used for:
Acid-base titration (Standardization of acids)
NaOH is a stable compound once in aqueous conditions and can be used as a primary standard for standardization procedures. Schools, colleges, and other educational laboratories use caustic soda for acid-base titrations. Generally, strong acids are standardized with caustic soda (sodium hydroxide).
Salt spray testing
Caustic soda is used in salt spray testing to balance the pH by mixing with acid. Salt spray testing is the corrosion test method used to check the corrosion resistance of the material surface coating.
It is used for cleaning purposes due to its corrosion properties. It can remove grease and oil deposits. It is also used for cleaning the sinks and draining pipes. Surfactants can be added to a solution of sodium hydroxide to stabilize the dissolved chemicals, which helps prevent their depositions. Their soaked solution is used as a degreaser on the surface of stainless steel.
Caustic soda is used for the production of detergents. These detergents can be used for several cleaning purposes. For example, it is used in parts washer machines to remove stains from the surface of materials. Caustic soda-based detergents are potent and aggressive cleaning chemicals.
Caustic soda is used as a drain opener for which it is widely consumed on the domestic level. It is found in liquid gel or dry crystal pallets. During a reaction with grease, it produces water-soluble substances and releases heat, dissolving the blocking substances in the drain pipes.
Relaxers are used for straightening the hair. Due to the high burning intensity, caustic soda is used in these relaxers.
Caustic soda can remove paint from the surface of materials, such as wood, door, gates, and houses. It is not regularly used as paint remover because of its corrosive nature.
pH control of the solution
Due to the fundamental alkaline behavior of caustic soda, it is used to control the solution’s pH, in food and pharmaceutical laboratories.
Esterification and transesterification reagent
Caustic soda is used as a catalyst in base-catalyzed esterification reagent in the saponification process (soap-making process). The hardness of soap depends on the amount of caustic soda used.
Caustic soda is used in the production of biodiesel. It acts as a catalyst for the transesterification of triglycerides and methanol during the reaction. This is only accomplished by using anhydrous caustic soda. The solution of caustic soda in water turns the fat into soap.
Sodium hydroxide is used as a catalyst in many chemical processes. For example, when in any reaction, a base is required as a catalyst to proceed. For such activities, the most common use of NaOH in laboratories is, as a catalyst.
Drinking water treatment
During the process of water purification, caustic soda is added to increase the water’s pH, decreasing the water’s corrosiveness and toxic metals that are dissolved in the water.
Tissue and protein digestion
Caustic soda can digest tissue and protein. Laboratories use caustic soda to digest animal dead bodies which are kept in a chamber, and an aqueous solution of caustic soda is added. This digests the animal’s flesh and tissues and converts them into a soap-like mixture (reaction with lipid content of flesh).
It can be used in research, experiments, and chemical compound detections. For example, the sodium hydroxide test detects flavonoids, which are chemical compounds found in plants.
EMPA researchers found that caustic soda (concentrated sodium hydroxide) can be used for domestic heating storage. When water is added to concentrated sodium hydroxide, it releases a large amount of heat energy due to an exothermic reaction. This heat energy can be stored as latent chemical energy.
Chemical compounds are used for neutron moderators in nuclear plants, and an experiment revealed that caustic soda can also be used for this purpose. As a neutron moderator in modern reactors, Seaborg technologies are still working with caustic soda.
Uses of caustic soda in food preparation
Caustic soda is used in the production and preparation of food.
- Caustic soda is used for the chemical peeling of fruits and green vegetables.
- It is also used to process chocolate, soft drink, and for the thickening of ice cream.
- Softening of olives can be achieved by soaking them in the solution of caustic soda.
- German pretzels and bagels can be crispy by using caustic soda.
- Lye water is also used in baked Chinese moon cakes and Chinese noodles.
- It is used in the production of century eggs for gelling appearance.
- Caustic soda is used in Norwegian or lutefisk dishes.
- It is used for achieving the sweet flavor of zongzi.
- It is also used to remove the skin of vegetables (potatoes, tomatoes).
Industrial applications of caustic soda
Industries use caustic soda for several purposes, such as production, refining, and purification. Following are some of the industrial applications of caustic soda:
Synthesis of organic chemicals
Caustic soda is used in industrial organic syntheses, such as pH control, off-gas scrubbing, dehydrochlorination, and neutralization of acids. It also acts as a catalyst during the industrial synthesis of organic compounds. It is employed in producing emulsion polymer isocyanates (EPI) and dehydrochlorination of epoxy resins.
Caustic soda is utilized in the formation of chelating agents by maintaining the pH of the solution. It is used in the synthesis of cellulose ether by reacting with cellulose and sodium monochlorocetate. It is used in the production of cellulose derivates, such as ethylcellulose, methylcellulose, and carboxymethyl hydroxyethyl cellulose.
Production of inorganic chemicals
Caustic soda is used to produce sodium hypochlorite (bleaching chemical). It synthesizes sodium cyanide and zeolites. It is also used to manufacture filler compounds such as sodium silicates and sodium phosphates.
The process of soap production is called saponification. Sodium hydroxide is called lye in the soap industry. It is used to increase the hardness of the soap, making it a hard soap. There are alternatives to caustic soda, such as potassium hydroxide, which is used to produce soft soaps (liquid soaps). Caustic soda is very cheap compared to potassium hydroxide, which is why it is used at the industry level to increase the yield at a minimum price.
In the paper industry, caustic soda is used in wood pulping to produce paper. In the Kraft process, it is utilized with sodium sulfide to remove the lignin from cellulose. In the bleaching process of brown pulp, it is used to remove lignin (oxygen lignification) and oxidative extraction.
There is a wide range of uses of caustic soda in the textile industry. It is used as a base medium for dyes used in textile and is also used to produce artificial fiber, Rayon.
Vegetable oil refining
The first step is the neutralization of trans fatty acids in vegetable oil synthesis. For this purpose, editable oils are treated with 10% solution of caustic soda and then processed further for bleaching and deodourization.
Caustic soda is used in the petroleum industry as an additive for drilling purposes. This provides cooling and lubrication to the surrounding area and also decreases the corrosion of drilling materials produced by acidic components.
Caustic soda enhances the recovery of petroleum components by dissolving the mud at a high pH level. It also reduces the interfacial tension between oil and rocks.
Dissolving amphoteric metals and compounds
Caustic soda is a basic medium for dissolving amphoteric metals and compounds, such as aluminum, zinc, and lead. For example, when caustic soda reacts with aluminum and water, it gives hydrogen gas and sodium aluminate as final products.
Sodium aluminate is very useful for the further production of compounds at industrial level. Similarly, the reaction of caustic soda with zinc and lead gives sodium zincate and sodium plumbate, respectively.
Caustic soda is used in cement manufacture for various purposes. It helps decrease the separation of silica and cement. It also reduces the amount of water required by a mixture of cement. This increases the strength of cement products.
Refining of ores
NaOH is used in refining ores to obtain the pure form of metals. For example, bauxite is an ore containing alumina which is used for the production of aluminum metal. After the crushing phase of bauxite mining, it is passed through high temperature along with sodium hydroxide to extract aluminum in the form of sodium aluminate solution.
What is sodium hydroxide (NaOH)?
It is a strong base that is used for industrial processes. It is commonly known as caustic soda.
How might you be exposed to sodium hydroxide?
During lab work, direct contact with sodium hydroxide should be avoided with the skin because it may cause burns and blisters.
How do you mix caustic soda with water?
Caustic soda is highly soluble in water. The solvation process evolves a huge amount of heat. Therefore, it should be added slowly and gradually to the water.
Will caustic soda remove rust?
Yes, caustic soda can remove rust without reacting with iron or steel.
How to get rid of caustic soda?
Alkaline solutions are gotten rid of by washing with water.
Can caustic soda be diluted with water?
The concentration of the caustic soda solution can be diluted by adding water.
What happens when caustic soda reacts with vinegar?
When caustic soda (base) reacts with vinegar (5% acetic acid solution), they neutralize each other.
What piping material is best for caustic soda?
Nickel alloy is best used as piping material for the transfer of sodium hydroxide.
- Handbook of Chlor-Alkali Technology Volume 1 by Thomas F. O’Brien, Tilak V. Bommaraju, Fumio