Caustic Soda (NaOH)

Last Updated : 21 Dec, 2023

Caustic Soda is a solid chemical compound that contains sodium (Na), oxygen(O), and hydrogen(H) ions. The chemical name of Caustic Soda is Sodium Hydroxide. The chemical formula of caustic soda is NaOH. Caustic Soda is basically a base as it releases OH^– ions when dissolved in water.

Caustic Soda is an important compound in chemistry as well as in daily life. In this article, we will learn What is Caustic Soda, what is its chemical formula, and its chemical name. We will also learn about the physical and chemical properties of Caustic Soda and the preparation of Caustic Soda along with its properties and uses.

Caustic-Soda

Table of Content

What is Caustic Soda(NaOH)?
Properties of Caustic Soda
Methods to Prepare NaOH
Caustic Soda Uses

What is Caustic Soda(NaOH)?

Caustic Soda is a strong basic compound formed with a combination of Sodium, Hydrogen, and Oxygen ions. Caustic Soda is a white-colored chemical compound with the chemical formula NaOH. Caustic Soda releases sodium (Na⁺) ions and hydroxide ions (OH^–) when you dissolve it in water. It is a strong alkali compound.

Chemical Name of Caustic Soda

Chemical name of Caustic Soda is ” Sodium Hydroxide”.

Chemical Formula of Caustic Soda

Chemical Formula of Caustic Soda is “NaOH”

Molecular Weight of Caustic Soda

Molecular Weight of Caustic Soda is 40g

Caustic Soda i.e. NaOH consists 3 elements which are Sodium (Na), Oxygen (O) and Hydrogen (H). We know that:

Atomic mass of Sodium = 23 g/mol

Atomic mass of Oxygen = 16 g/mol

Atomic mass of Hydrogen = 1 g/mol

Now,

Molecular weight of NaOH = atomic mass of Na + atomic mass of O + atomic mass of H

Molecular weight of NaOH = 23 + 16 + 1

Molecular weight of NaOH = 40 g/mol

Hence, the molecular weight of NaOH is 40 g/mol.

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Properties of Caustic Soda

Now, you have completely understand the definition of caustic soda and its reaction with water. It is high time, you move to its properties. There are 2 main kinds of properties of Caustic Soda (NaOH):

Physical properties
Chemical properties

Physical Properties of NaOH

State: NaOH is generally found in solid states such as flakes, beads etc. It is white in color in solid form.
Solubility: NaOH has high solubility in water which means it gets instantly dissolved when mixed with water.
Transformation: When NaOH gets mixed in H₂O, it changes from solid state to liquid state instantly.
Heat Generation: NaOH generates a significant amount of heat while performing reaction with water as this reaction is exothermic. This is an important property for concentrated solutions of NaOH.
Density: The density of NaOH is directly proportional to the concentration of NaOH in the solution. NaOH solutions have higher density than water.

Chemical Properties of NaOH

Alkalinity: NaOH shows strong alkaline properties. It is a strong base. When you dissolve it in water, it releases OH^–ions and forms an alkaline solution.
Reactivity with Acids: NaOH can react with acids strongly in neutralization reaction. The general equation is:

NaOH (aq) + HCl (aq) → NaCl (salt) + H2O (l)

Hydrolysis reaction: In this reaction, NaOH is specifically involved with esters to produce alcohols and other compounds. Let’s take a basic reaction to understand the hydrolysis reaction:

CH₃COOC₂H^– (ethyl acetate) + NaOH ) → CH₃COONa (sodium acetate) + C₂H^–OH (ethanol)

Corrosive Nature: NaOH is highly corrosive in nature. Direct contact with skin or eyes can cause you severe burns.
Saponification Process: During soap-making process, NaOH plays an essential role. It reacts with fats and oils to produce soap and glycerine.

Caustic Soda Reaction with Water

Caustic Soda has three elements Na, O and H. Let’s see a basic chemical reaction of NaOH interacting with water below:

NaOH (s/l) + H₂O (water) → Na⁺ (aq) + OH^– (aq) + H₂O (l)

The above reaction is showing that when NaOH reacts with water, it releases sodium ions (Na+) and hydroxide ions (OH-). This is an highly exothermic reaction, means that this reaction releases some amount of heat.

Methods to Prepare NaOH

Caustic Soda aka NaOH or Sodium Hydroxide can be prepared by various methods which are given below:

Nelson-Diaphragm Cell Method
Loewig’s Process
Castner-Kellner Process

These are a couple of industrial methods by which NaOH can be prepared. Let’s discuss Nelson-Diaphragm method among them:

Nelson-Diaphragm Cell Method

This is an industrial methods and essential for large-scale industries to produce caustic soda. This method offers a way to produce NaOH while we keep sodium hydroxide and chlorine separately in this method.

The chemical reaction of Nelson-Diaphragm Cell method is:

2NaCl (salt) + 2H₂O (water) + electricity → Cl₂ (chlorine) + H₂ (Hydrogen) + 2NaOH (Sodium Hydroxide)

Let’s understand this process in following steps:

Step 1: An electrolytic cell consists a container which has 2 compartments: 1) Anode Compartment, 2) Cathode Compartment. These 2 compartments are separated by a diaphragm. This diaphragm is made by asbestos. At anode compartment, Cl ions are present and in cathode compartment, OH ions are present.

Step 2: Now, you should have a brine solution which is typically formed by dissolving NaCl (Sodium Chloride) in H₂O (water). This brine solution acts as an electrolyte and important for an efficient process.

Step 3: Using electrodes, an electric current is being passed through this brine solution.

Step 4: At anode compartment (Positive electrode), Cl ions are oxidized to form chlorine gas (Cl2):

2Cl^– → Cl^– + 2e^–

Step 5: At cathode compartment (negative electrode), water is reduced to form hydroxide ions and hyrogen ions:

2H₂O + 2e^– → H₂ + 2OH^–

Step 6: These hydroxide ion (OH^–) travels through the diaphragm to the anode compartment and reacts with sodium ions (Na⁺) to form sodium hydroxide:

Na⁺ + OH^– → NaOH

Step 7: Now, chlorine gas is collected at the anode., hydrogen gas is collected at the cathode and sodium hydroxide is also collected from cathode compartment. Chlorine and sodium hydroxide can’t be mixed due to diaphragm.

Step 8: The collected products undergo a purification process to ensure the quality and purity of chlorine, hydrogen and sodium hydroxide.

Step 9: The overall reaction is as follows:

2NaCl (salt) + 2H₂O (water) + electricity → Cl₂ (chlorine) + H₂ (Hydrogen) + 2NaOH (Sodium Hydroxide)

Loewig’s Process

Loewig’s Process includes the electrolysis of sodium chloride (NaCl) solution. In this process, a brine solution (NaCl dissolved in water) serves as the electrolyte. The chemical reactions occurring at each electrode are:

At the time of electrolysis, chlorine gas is produced at the anode:

2Cl^– → Cl₂ + 2e^–

At the cathode, hydrogen gas and sodium hydroxide are formed:

2H₂O + 2e^– → 2OH^– + H₂

Now, the complete reaction will be:

2NaCl + 2H₂O → Cl₂ + H₂ + 2NaOH

Read More about Elctrochemical Cell.

Castner-Kellner Process

The Castner-Kellner Process also includes electrolysis process but has different setup. In this method, mercury cathode cells are used.

At the cathode, Sodium amalgam is formed:

2Na⁺ 2e^– → 2Na

It reacts with water to form sodium hydroxide and hydrogen gas:

2Na + 2H₂O → 2NaOH + H₂

Here, the chemical reaction has produced NaOH.

Caustic Soda Uses

Now, it’s time to know about the real life uses of NaOH:

Cleaning Agent: NaOH reacts with fats and oils to produce soaps and detergents. This process is called saponification process. In this way, NaOH contributes to the cleanliness and hygiene of households. It is the best cleaning agent due to its ability to break down grease and stains.
Textile Industry: NaOH is used in dyeing and finishing textiles. It helps in processes like mercerization which strengthen the luster of cotton fibres.
Water Treatment: Caustic Soda adjusts the pH levels of water. It removes the impurities of water.
Aluminium Production: NaOH helps to extract alumina by refining bauxite ore. This alumina is then used to produce aluminium metal.
Food Processing: NaOH is used to make some traditional foods. It is highly used in food processing tasks such as peeling fruits and vegetables.

Also, Check

Sodium Chloride

Acid, Base and Salts

Sodium Carbonate