Caustic Soda - Preparation and Uses

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What is Caustic Soda?

Sodium hydroxide, also known as caustic soda, and lye, is an inorganic compound with NaOH as caustic soda formula. It is a white-colored solid ionic compound consisting of hydroxide anions OH and sodium cations Na+.

It's a highly caustic base and the alkali that decomposes proteins at ordinary ambient temperatures and can severely burn chemical burns. It readily absorbs carbon dioxide and moisture from the air and is highly soluble in water. It creates a series of hydrates NaOH·nH2O. 


Note: The monohydrate NaOH·H2O crystallizes from the water solutions between the temperatures of 12.3 and 61.8 °C. "Sodium hydroxide," which is commercially available, is often this monohydrate, and published data can refer to it instead of anhydrous compound. It is frequently utilized as one of the simplest hydroxides alongside acidic hydrochloric acid and neutral water to demonstrate the chemistry students' pH scale.


Preparation of Caustic Soda

Sodium hydroxide or Caustic Soda can be prepared by three successive methods as given below:

  • Castner-Kellner process

  • Nelson Diaphragm cell

  • Loewig's process

Let us now discuss the Castner-Kellner process in brief.

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Castner-Kellner Process


Principle

In the process of Castner-Kellner, electrolysis of brine solution is performed to obtain the sodium hydroxide.


Castner-Kellner cell

It is a rectangular steel tank, where the ebonite is lined inside the tank. The titanium acts as an anode, and a mercury layer, residing at the bottom of the tank, acts as the cathode.


Ionization of Brine Solution takes Place according to the Following Reaction:

2NaCl → 2Na+ + 2Cl-


When the brine solution gets in contact with an electric current, ionization takes place. As a result, both the positive and negative ions move towards the electrodes. And, the sodium ions get deposited at the mercury cathode by forming a sodium amalgam. In contrast, chlorine ions move towards the anode position and exit the cell from the top.

Reaction at the Anode:

2Cl- → Cl2 + 2e-

Reaction at the Cathode:

2Na+ + 2e- → 2Na

Nelson Diaphragm Cell

Principle

Electrolyte used in this process is an aqueous NaCl solution (also called Brine).


Procedure

The porous diaphragm of metal oxide or asbestos with the polymer separates cathode and anode compartments. Diaphragm prevents the hydroxide ions, entering the anode compartment, and prevents the chloride ions, entering the cathode compartment. The saturated brine enters into the anode compartment, and resultantly, chlorine gas is produced.


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Anode (otherwise called a Positive Electrode): Carbon (otherwise called graphite) or titanium is coated with the Ru-Ti oxide.


Cathode (or called a negative electrode): Steel Mesh

Reaction at Anode (or Oxidation)

2Cl- (aq) àCl2(g) + 2e

Cathode Reaction (or Reduction)

2H2O (l) + 2e à H2(g) + 2OH- (aq)


Na+ migrates across the diaphragm to the cathode compartment by combining with OH- to form NaOH.


Overall Cell Reaction (Showing the Na+ Spectator Ions)

2H2O (l) + 2Cl- (aq) + 2Na+ (aq) → 2Na+ (aq) + 2OH- (aq) + H2(g) + Cl2(g)


This product contains sodium hydroxide and sodium chloride, and the NaOH(s) can be crystallized out.


Loewig's Process

The process of Loewig for the preparation of caustic soda depends on the formation of sodium ferrate (Na2FeO4) and then decomposed with water. Thereafter, the soda liquors mix with ferric oxide and mass evaporated to dryness and calcined at a bright red heat, usually in a revolving furnace. By the process of calcination, a reaction between the iron oxide and sodium carbonate is brought about, escaping the carbon dioxide and remaining sodium ferrate in the furnace.

The mass is washed with the cold water until the total soluble matter is removed; then, water at 900 °C is run over the sodium ferrate. It is decomposed, forms caustic soda, and the iron oxide is regenerated. The last is returned to the process of calcining. Ferric oxide, which is used, is natural iron ore, free and very clean from silica or other impurities; made by calcining a precipitated ferric hydroxide is not adapted well to the process, because it forms a product, which is difficult to lixiviate.


Caustic Soda Uses and Benefits

Sodium hydroxide or caustic soda is used to manufacture various everyday products, including aluminum, paper, commercial drain, oven cleaners, and detergents & soaps.

Let us look at it in brief.


Sodium Hydroxide in Cleaning and Disinfectant Products

Sodium hydroxide or caustic soda is used to manufacture soaps and various detergents we use in homes and commercial applications. The chlorine bleach is formed by combining sodium hydroxide and chlorine. Drain cleaners containing caustic soda convert the fats, grease that may clog pipes into soap, dissolves in water.


Application of Caustic Soda

Caustic soda is used in various industries: in the manufacturing of paper and pulp, drinking water, textiles, detergents & soaps, and also as a drain cleaner. The worldwide production of caustic soda as per 2004 was approximately 60 million tonnes, while the demand was about 51 million tonnes. The caustic soda chemical name is Sodium Hydroxide and the chemical formula of caustic soda is NaOH.

FAQ (Frequently Asked Questions)

1. Explain the Properties of Caustic Soda and mention its Usage in Energy?

Ans: Properties of Caustic Soda

  • It is a stable compound.

  • It is a white-colored solid with a melting point of 591K.

  • It is soluble in water highly and soluble in alcohol moderately.

  • NaOH is bitter, and it has a soapy feel to it.

  • Caustic Soda is also strongly alkaline in nature.


Let us look at the uses of caustic soda in daily life.


Caustic Soda in Energy

In the energy industry, caustic soda is used in fuel cell production. These fuel cells work like batteries to produce electricity cleanly and efficiently for various applications, such as transportation, handling materials, portable, stationary, and emergency backup power applications. Also, the epoxy resins are manufactured with caustic soda, are used in wind turbines.

2. Why do we call Sodium Hydroxide as Caustic Soda?

Ans: Sodium hydroxide is also called soda or lye, or even caustic soda. Here, caustic means' burning', and the caustic soda takes its name the way it can burn the skin, and it has a chemical formula of NaOH.


At room temperature, the Sodium hydroxide or Caustic Soda is a white-colored crystalline odorless solid that absorbs moisture from the air, and it is a synthetically manufactured substance. We can say it is a versatile alkali. It is mainly used in the manufacturing of paper, soap & detergents, alumina, petroleum & chemical products. A few other applications include textiles, water treatment food, mining glass making, metal processing.

3. List the Practical uses of Caustic Soda?

Ans: Caustic Soda has various uses such as anti-pesticide, cleaning, inorganic uses of chemistry such as creating electricity, which is used in the Castner-kellner cells.

4. What happens if Caustic Soda is mixed with Bleach?

Ans: Bleach can be made by mixing caustic soda with chlorine gas, and is shipped with a less amount of caustic soda still remaining. Adding more bleach will just raise the solution pH level, from 10.5+ up to 14.