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Caustic Soda Preparation Properties and Uses - Check Here

Caustic Soda Preparation Properties and Uses - Check Here

Team Careers360Updated on 02 Jul 2025, 04:27 PM IST

Sodium hydroxide, also called as caustic soda or lye, is an inorganic chemical having the caustic soda formula NaOH. It's a white solid ionic compound made up of sodium cations Na+ and hydroxide anions OH-. NaOH chemical name is caustic soda and sodium hydroxide chemical formula is NaOH. It is highly soluble in water and easily absorbs carbon dioxide and moisture from the air. It produces a series of NaOH.nH2O hydrates. Caustic soda chemical name is Sodium Hydroxide.

Caustic Soda Preparation

This Story also Contains

  1. Castner - Kellner Process
  2. Nelson Diaphragm Cell
  3. Loewig's Process
  4. Caustic Soda Uses:
  5. Caustic Soda Applications
Caustic Soda Preparation Properties and Uses - Check Here
Caustic soda preparation, preparation and Uses

The following three processes can be used to make sodium hydroxide or Caustic soda:

  1. Castner-Kellner process

  2. Nelson Diaphragm cell

  3. Loewig's process

Castner - Kellner Process

Principle: Electrolysis of brine solution is used in the Castner-Kellner procedure to obtain sodium hydroxide.

Castner-Kellner cell

It's a rectangular steel tank with ebonite lining on the interior. The titanium serves as an anode, while a mercury layer at the tank's bottom serves as a cathode.

The reaction that causes the ionization of the brine solution is as follows:

2NaCl → 2Na+ + 2Cl-

Ionization occurs when the brine solution comes into touch with an electric current. Both positive and negative ions travel toward the electrodes as a result. By generating a sodium amalgam, the sodium ions are deposited at the mercury cathode. Chlorine ions, on the other hand, travel towards the anode and exit the cell from the top.

At the anode, the reaction is as follows:

2Cl- → Cl2 + 2e-

At the cathode, the reaction is as follows:

2Na+ + 2e- → 2Na

Commonly Asked Questions

Q: What is the difference between anhydrous caustic soda and its hydrates?
A:
Anhydrous caustic soda (NaOH) contains no water molecules, while hydrates like sodium hydroxide monohydrate (NaOH·H2O) have water molecules incorporated into their crystal structure. Hydrates have different physical properties, such as melting points, compared to the anhydrous form.
Q: What is the heat of solution of caustic soda, and why is it important?
A:
The heat of solution of caustic soda is highly exothermic, meaning it releases a significant amount of heat when dissolved in water. This is important because it can lead to dangerous situations if not handled properly. When adding caustic soda to water, the solution can quickly become hot enough to boil, potentially causing splashing of the corrosive solution.

Nelson Diaphragm Cell

Principle: An aqueous NaCl solution is used as the electrolyte in this process (also called Brine).

Procedure:

The metal oxide or asbestos porous diaphragm with the polymer divides the cathode and anode chambers. The diaphragm keeps hydroxide ions out of the anode compartment while keeping chloride ions out of the cathode compartment. The saturated brine reaches the anode compartment, resulting in the production of chlorine gas.

Also read :

NCERT Exemplar Class 11th Chemistry Solutions

NCERT notes Class 11 Chemistry Chapter 10 The S-Block Elements
NCERT Exemplar Class 12th Chemistry SolutionsNCERT solutions for Class 11 Chemistry Chapter 10 The S-Block Elements
NCERT Exemplar Solutions for All SubjectsNCERT Exemplar Class 12 Chemistry solutions Chapter 10 The S-Block Elements


Positive electrode

Ru-Ti oxide is used to coat carbon (also known as graphite) or titanium.

Cathode /Negative electrode- Steel Mesh

Reaction at Anode / Oxidation

2Cl- (aq) → Cl2 (g) + 2e-

Cathode Reaction / Reduction

2H2O (l) + 2e- → H2 (g) + 2OH- (aq)

Mixing with OH- creates NaOH, and Na+ migrates through the diaphragm to the cathode compartment.

Overall Cell Reaction (Showing Na+ Ions)

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

The NaOH(s), which contain sodium hydroxide and sodium chloride, can be crystallized out of this product.

Related Topics

Loewig's Process

The Loewig technique is used for making caustic soda and is based on the creation of sodium ferrate (Na2FeO4), which is then decomposed with water. The soda liquors are then combined with ferric oxide, and the mixture is evaporated to dryness before being calcined at a bright red temperature, usually in a revolving furnace. Calcination causes a reaction between iron oxide and Sodium Carbonate, resulting in the release of carbon dioxide and the retention of sodium ferrate in the furnace.

The bulk is rinsed in cold water until all soluble stuff has been removed, and then 900°C water is poured over the sodium ferrate. It decomposes, producing caustic soda and regenerating iron oxide. The last is returned to the calcining process. The ferric oxide utilized is natural iron ore that is free of silica and other impurities; ferric hydroxide that has been precipitated is not well suited to the process since it produces a product that is difficult to lixiviate.

Properties of Caustic Soda

  • It's a white solid with a melting point of 591K.
  • It's a long-lasting substance.
  • NaOH is bitter and soapy to the touch.
  • It has a high water solubility and a moderate solubility in alcohol.
  • Sodium hydroxide is an alkaline substance.
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Commonly Asked Questions

Q: How is caustic soda prepared industrially?
A:
Caustic soda is primarily produced through the chloralkali process. This involves the electrolysis of a sodium chloride (table salt) solution, which produces chlorine gas, hydrogen gas, and sodium hydroxide solution. The overall reaction is 2NaCl + 2H2O → Cl2 + H2 + 2NaOH.
Q: What is the environmental impact of caustic soda production and use?
A:
The production of caustic soda through the chloralkali process consumes significant energy and can lead to chlorine emissions if not properly controlled. Its use can lead to high pH in wastewater, potentially harming aquatic ecosystems if not properly treated. However, it's also used in environmental applications like flue gas desulfurization.
Q: What is the difference between liquid caustic soda and solid caustic soda?
A:
Liquid caustic soda is a solution of sodium hydroxide in water, typically 50% by weight. Solid caustic soda is anhydrous sodium hydroxide in the form of pellets, flakes, or beads. Liquid caustic soda is easier to handle and dilute but has a lower concentration, while solid caustic soda is more concentrated but requires more careful handling.

Caustic Soda Uses:

  • Aluminum, paper, industrial drain and oven cleaners, and detergents and soaps are all made with sodium hydroxide formula NaOH (also known as caustic soda).
  • Cleaning and disinfectant products containing sodium hydroxide
  • Soaps and other detergents that we use in our homes and businesses are made from sodium hydroxide, sometimes known as caustic soda. Sodium hydroxide and chlorine are combined to make chlorine bleach. Drain cleaners using caustic soda break down the fats and grease that can clog pipes into soap.

Commonly Asked Questions

Q: Why is caustic soda used in drain cleaners?
A:
Caustic soda is a common ingredient in drain cleaners due to its ability to break down organic matter like hair, grease, and food particles that often cause clogs. It also reacts with fats to form soap, which can help in further cleaning. However, its corrosive nature means it must be used cautiously to avoid damaging pipes.
Q: How does caustic soda affect the pH of water?
A:
Caustic soda significantly increases the pH of water due to the release of hydroxide (OH-) ions. Even small amounts can raise the pH to 13 or 14, making the solution extremely alkaline. This property is why it's often used in pH adjustment applications.
Q: What is the role of caustic soda in the Bayer process for aluminum production?
A:
In the Bayer process, caustic soda is used to dissolve aluminum oxide (Al2O3) from bauxite ore. It forms sodium aluminate, which can then be separated from impurities. The aluminum is later recovered through precipitation and calcination.
Q: How does caustic soda contribute to the production of paper?
A:
In paper production, caustic soda is used in the kraft process to break down wood chips into wood pulp. It helps separate lignin from cellulose fibers, which is crucial for producing high-quality paper. The process involves cooking wood chips in a solution of caustic soda and sodium sulfide.
Q: How does caustic soda affect proteins?
A:
Caustic soda denatures proteins by breaking hydrogen bonds and disrupting the protein's secondary and tertiary structures. This process can change the protein's physical properties and biological function, which is why caustic soda is effective at breaking down organic matter.

Caustic Soda Applications

Caustic soda is utilized in a variety of industries, including paper and pulp production, drinking water, textiles, detergents and soaps, and drain cleaning. As of 2004, the global production of caustic soda was around 60 million tonnes, whereas the consumption was around 51 million tonnes. Sodium Hydroxide is the chemical term for caustic soda, and its chemical formula is NaOH. Sodium hydroxide common name is caustic soda and the chemical formula of caustic soda is NaOH.

Also read -

NCERT Solutions for Class 11 ChemistryNCERT notes Class 11 Chemistry
NCERT Solutions for Class 12 ChemistryNCERT notes Class 12 Chemistry
NCERT Solutions for All SubjectsNCERT Notes For All Subjects


Commonly Asked Questions

Q: What is caustic soda, and why is it called "caustic"?
A:
Caustic soda is the common name for sodium hydroxide (NaOH). It's called "caustic" because it's highly corrosive and can cause severe chemical burns on contact with skin or other tissues. The term "caustic" refers to its ability to break down or dissolve organic matter.
Q: What is the difference between caustic soda and lye?
A:
There is no difference. "Lye" is another common name for sodium hydroxide (NaOH). Both terms refer to the same chemical compound, with "caustic soda" being more commonly used in industrial settings and "lye" in household or artisanal contexts.
Q: How does caustic soda react with acids?
A:
Caustic soda reacts with acids in a neutralization reaction, forming water and a salt. For example, when it reacts with hydrochloric acid (HCl), it forms sodium chloride (table salt) and water: NaOH + HCl → NaCl + H2O. This reaction is highly exothermic, releasing heat.
Q: Why is caustic soda stored in plastic containers instead of glass?
A:
Caustic soda is stored in plastic containers because it can react with silica in glass, potentially weakening or etching the glass over time. Certain plastics, like polyethylene or polypropylene, are resistant to caustic soda's corrosive effects.
Q: How does caustic soda contribute to the manufacture of soap?
A:
Caustic soda is a key ingredient in soap making through a process called saponification. It reacts with fats or oils to produce soap and glycerin. The strong base breaks down the triglycerides in fats, forming fatty acid salts (soap) and glycerol.

Frequently Asked Questions (FAQs)

Q: What is the role of caustic soda in the production of certain types of paint?
A:
In paint production, caustic soda can be used to neutralize acidic components, adjust pH, and saponify oils in certain formulations. It's particularly important in the production of water-based paints, where it can help emulsify oils and improve the stability of the paint. It can also be used to produce certain pigments used in paints.
Q: How does caustic soda contribute to the process of oil refining?
A:
In oil refining, caustic soda is used in several stages. It's used to remove naphthenic acids and other acidic contaminants from crude oil in a process called caustic washing. It also helps in the removal of sulfur compounds, reducing the overall sulfur content of the refined products. Additionally, it's used in the treatment of various petroleum fractions to improve their quality.
Q: Why is caustic soda used in the production of some types of ceramics?
A:
In ceramics production, caustic soda can be used as a flux, lowering the melting point of other materials and promoting vitrification. It can also be used to adjust the pH of ceramic slips and glazes, affecting their rheological properties. In some cases, it's used to create specific surface effects on ceramic pieces.
Q: How does caustic soda affect the solubility of heavy metals in water?
A:
Caustic soda can affect the solubility of heavy metals in water by changing the pH. At high pH levels caused by caustic soda, many heavy metals form insoluble hydroxides and precipitate out of solution. This property is used in water treatment to remove heavy metal contaminants. However, some metals, like chromium, can form soluble hydroxide complexes at very high pH.
Q: What is the role of caustic soda in the production of cellulose ethers?
A:
Caustic soda is crucial in the production of cellulose ethers like carboxymethyl cellulose (CMC). It's used to activate the cellulose by breaking hydrogen bonds and making the hydroxyl groups more reactive. This allows for the subsequent etherification reaction. The concentration of caustic soda used can affect the properties of the final product.
Q: How does caustic soda contribute to the process of leather tanning?
A:
In leather tanning, caustic soda is used in the liming process. It helps to remove hair from the hides and to open up the fiber structure of the collagen in the skin. This prepares the hide for the tanning process by making it more receptive to the tanning agents. Caustic soda also helps to remove fats and proteins from the skin.
Q: Why is caustic soda used in the production of some types of batteries?
A:
Caustic soda is used as the electrolyte in alkaline batteries. It provides the hydroxide ions necessary for the electrochemical reactions that generate electricity. The high conductivity of caustic soda solutions makes them effective electrolytes. It's also used in the production of some rechargeable batteries, like nickel-cadmium batteries.
Q: How does caustic soda affect the properties of glass?
A:
Caustic soda can etch and weaken glass over time by reacting with the silica in the glass. This reaction forms sodium silicate, which can cause the glass to become cloudy or even structurally compromised. This is why caustic soda solutions are not typically stored in glass containers for extended periods.
Q: What is the role of caustic soda in the production of synthetic fibers?
A:
Caustic soda is used in the production of various synthetic fibers. In viscose rayon production, it's used to treat cellulose, creating alkali cellulose. In the production of lyocell fibers, it's used in the recovery of the solvent. It's also used in the production of some polyester fibers to control pH during polymerization.
Q: How does caustic soda contribute to the extraction of gold from ore?
A:
In gold extraction, caustic soda is used in conjunction with cyanide in a process called cyanidation. The caustic soda helps maintain a high pH (around 10-11), which is necessary for the cyanide to effectively dissolve gold. It also helps in the precipitation of impurities and in the regeneration of cyanide.
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