These handmade soaps look beautiful, isn’t it? But what do you think exactly goes into making them? It needs a combination of two major ingredients! Oils and sodium hydroxide. Apart from these, there are always infinite scopes of customising soaps in terms of colour additives, fragrances and shaping them into various moulds.
Sodium hydroxide in particular has endless possibilities for usage in multi-dimensional industries. It is like a fatherly figure in chemistry, responsible for the formation of so many compounds of immense importance and through its varied properties, fulfilling various kinds of chemical needs!
TABLE OF CONTENTS
Sodium hydroxide, is an inorganic chemical compound that is normally found as a white translucent solid at ambient temperature. It is a strongly alkaline, ionic compound which is also hygroscopic in nature. It is formed by an ionic bond between and ions.
It is also commonly known as caustic soda or Lye and is widely used in the manufacturing of soap, detergents, pulp and paper, explosives, liquid drains, oven cleaners, etc.
The structure of the sodium hydroxide molecule is made from an ionic bond formed between and when the cation transfers one electron to the anion. Overall sodium hydroxide is neutral. and its monohydrate form orthorhombic crystals. Each sodium atom is surrounded by three hydroxyl anions and 3 water molecules.
The hydrogen atoms of the hydroxyl group form a strong bond with oxygen atoms within each oxygen layer. Nearby oxygen layers are held together by hydrogen bonds between water molecules.
One of the most powerful bases is sodium hydroxide (). It is also one of the most commonly utilised alkali hydroxides in laboratories and in industry. It is most commonly made by electrolysis of salt solution in a diaphragm or Mercury cell.
Preparation of Sodium Hydroxide by Chloralkali Process
The chloralkali process produces sodium hydroxide, including chlorine and hydrogen. This is done by electrolysis of a sodium chloride solution  .
At the cathode, where water is converted to hydrogen gas as well as hydroxide ions.
Hence in Chlor-alkali process, during electrolysis:
It is necessary to prevent the from reacting with the in order to produce . This is usually accomplished in one of three ways, with the membrane cell technique being the most cost-effective.
Three production methods are used as mentioned below:
A Nafion membrane is used to segregate the cathode and anode processes. This process is quite identical to the diaphragm cell method. The membrane allows just sodium ions and a small amount of water to pass through. It generates of greater purity. 
Preparation of Sodium Hydroxide from Brine solution: Castner-Kellner cell
Sodium hydroxide is commercially prepared by the electrolysis of aqueous sodium chloride solution (brine solution) in a Castner-Kellner cell which applies the same principle as chlor-alkali process.
A mercury cathode is used here. Brine solution is electrolysed using a mercury cathode and a carbon (graphite) anode. and will dissociate into its constituent ions.
In this cell, the mercury flows along the bottom of the cell and acts as a cathode. The brine solution flows in the same direction and the anode consists of several graphite blocks. Sodium metal discharged at the cathode combines with mercury to form sodium amalgam. gas is released at the anode. This sodium amalgam is taken to another container where it will react with water to form
The reactions happening on the electrodes in this process are given as follows:
At Graphite anode (positively charged electrode): Chlorine gas is evolved at anode.  value of oxygen is higher than chlorine gas due to the overpotential of . This is why hydroxide ions are not oxidised at anode and chloride ions get oxidised owing to its overall lower electrode potential.
At the Mercury cathode (negatively charged electrode): Sodium metal is discharged at the cathode and it combines with mercury to form sodium amalgam.  Since the cathode is itself mercury, it readily forms an amalgam with sodium. This layer at the cathode will therefore prevent the reduction of hydrogen ions and prevent the liberation of hydrogen gas at the cathode.
This sodium amalgam reacts with water and will give sodium hydroxide and hydrogen gas.
Mercury is then re-circulated in the cell. and are two major by-products obtained in this process.
Preparation of Sodium Hydroxide from Sodium Carbonate solution
Preparation of pure Sodium Hydroxide
Commercial is purified with the help of alcohol. dissolves in alcohol while the impurities will remain insoluble. The alcoholic filtrate is distilled and then the alcohol distils off white pure solid sodium hydroxide.
https://www.youtube.com/watch?v=Ja1Xa-AENIA  
Aluminium hydroxide forms a gelatinous precipitate which can also be identified easily.
Applications of Sodium Hydroxide
Health Hazards of Sodium Hydroxide
Q.1. Sodium hydroxide is soluble in:
Solution: is ionic and polar in nature consisting of two oppositely charged ions and . So it is soluble in polar solvents like water. So, option (C) is the correct answer.
Q.2. What is the of an aqueous solution of ? 
Hence, = 0.1 M
Sodium hydroxide is strongly basic and hence it has a very high value of 13.
Q.3. What is the observation when a sample of ferrous sulphate salt is treated with sodium hydroxide? 
Green coloured precipitates of ferrous hydroxide is observed, which is an insoluble hydroxide.
Q.4. What is meant by causticizing? Express in terms of a chemical equation.
Answer: The formation of sodium hydroxide by treating sodium carbonate with calcium hydroxide in a double displacement reaction is called causticizing. Where out of the products formed sodium hydroxide is soluble, while calcium carbonate is not.
Frequently Asked Question-FAQs
Q.1. What is sodium hydroxide used for?
Answer: Sodium hydroxide is used in making soaps, and detergents used in homes and business applications. By combining chlorine and sodium hydroxide, chlorine bleach is made. Also, it is used as cleansing agents, dishwashing agents etc.
Q.2. Is sodium hydroxide soluble in alcohol?
Answer: Since it is polar and ionic in nature, it has very low solubility in organic solvents like methanol and ethanol. It is highly soluble in water.
Q.3. What is the major point of difference between and ?
Answer: resembles in almost all reactions & its properties are also similar to . Only difference is that is more soluble in alcohol. Hence, we use alcoholic for specific organic reactions and not alcoholic.
Q.4. Is sodium hydroxide good for the skin?
Answer: Sodium hydroxide causes strong irritation and is corrosive to the skin, hair, breathing tract and digestive system. Soap instead which is prepared by the process of saponification of triglycerides (long-chain fatty acids) and sodium hydroxide is safer on the skin.