Sodium Hydroxide

Sodium Hydroxide belongs to the category of inorganic compounds and is usually found in the form of a white solid at room temperature. This chemical compound consists of sodium cations and hydroxide anions. Sodium Hydroxide chemical formula is written as NaOH. Sodium Hydroxide is also popularly known as caustic soda or Iye.



Sodium Hydroxide / Sodium oxidanide
Chemical Formula NaOH
Molar Mass 39.997 g/mol
Density 2.13 g/cm³
Melting Point 318.4 oC
Boiling Point 1.388 °C
Hydrogen Bond Donor Count 1
Hydrogen Bond Acceptor Count 1
Rotatable Bond Count 0
Isotope Atom Count 0
Covalently-Bonded Unit Count 2

Properties of Sodium Hydroxide

Physical Properties of Sodium Hydroxide

  • Sodium Hydroxide in its pure form is a white crystalline solid.
  • It is odourless.
  • It is soluble in water, glycerol and ethanol. When solid sodium hydroxide is mixed with water it results in a highly exothermic reaction.
  • Has a higher viscosity than water about 78 mPas.
  • It can form several hydrates.
  • It can rapidly absorb carbon dioxide and water from the air. It can also exist in the form of a liquid.

Chemical Properties of Sodium Hydroxide

  • It has an ionic bond.
  • It can react with protic acids to form water and salts.
  • It has high acidity of 13.

Sodium Hydroxide Preparation

Sodium hydroxide (NaOH) is one of the strongest bases available. It is one of the most Important Alkali hydroxides used for laboratory and commercial purposes. Predominantly it is prepared by electrolysis of brine solution in diaphragm or Mercury cell. Historically there are few important processes through which NaOH is produced along with other products (Cl2, Na2CO3, etc.,)

(i) Leblanc Process:

In this, the Major product is chlorine gas but NaOH is produced as a side product. The overall equation of Leblanc process goes like this 4HCl+Mna22Cl2+Mn2++2H2O4HCl+Mn{{a}_{2}}\to 2C{{l}_{2}}+M{{n}^{2+}}+2{{H}_{2}}O.

Here MnO2 acts as an oxidising agent, oxidising HCl to Cl2. In olden days, preparation of HCl is difficult. It is prepared from NaCl by the action of a strong acid

NaCl + conc. H2SO4 → NaHSO4 + HCl

NaHSO4 + NaCl → Na2SO4 + HCl

Then, HCl produced is oxidised

HCl + MnO2 → Cl2 + Mne+

The side product Na2SO4 is used for making other chemicals such as glass, Na2CO3 or NaOH as follows.

Na2SO4 + C + CaCO3 → Na3CO3 + CaSO4

Na2CO3 + Ca(OH)2 → 2 NaOH + CaCO3

Here, the starting materials are H2SO4, NaCl, CaCO3 and C. NaOH and Cl2 are the main products. CaCO3 is converted to Ca(OH)2 as follows

CaCO3ΔCaOH2OCa(OH)2CaC{{O}_{3}} \overset{\Delta }{\rightarrow}CaO\overset{H_{2}O}{\rightarrow}Ca{{\left( OH \right)}_{2}}

(ii) Weldon’s Process:

It is similar to the Leblanc process and the only difference is Mn2+ (MnCl2) is recycled in Weldon but is wasted in Leblanc. Therefore Weldon’s process is a cheaper Method than Leblanc process

(iii) Deacon Process:

Similar to the above process, here also HCl is oxidised. But here the air is used to oxidise HCl in the presence of a catalyst (CaCl2)

Deacon Process Reaction



(iv) Electrolytic Process:

In this process, NaOH and Cl2 are produced by electrolysis of Brine (NaCl) solution. The electrolytic cell contains both cathode and anode to be graphite rods and the electrolyte being NaCl solution. The construction is as follows.Electrolytic Process

In the Brine solution Na+ and ClΘC{{l}^{\Theta }} ions are produced and due to the potential difference created, Na+ andClΘC{{l}^{\Theta }} move towards their oppositely charged electrodes i.e., Na+ moves towards cathode and ClΘC{{l}^{\Theta }} towards anode.

At anode: 2ClΘCl2+2e2C{{l}^{\Theta }}\to C{{l}_{2}}+2{{e}^{-}}

At cathode: Na+ + e → Na

2Na + H2O → NaOH + H2

Other than the above reactions some side reaction might also occur as follows.

NaOH+Cl2NaCl+NaOCl+H2ONaOH+C{{l}_{2}}\to NaCl+NaOCl+{{H}_{2}}O OHΘO2+2H2O+4eO{{H}^{\Theta }}\to {{O}_{2}}+2{{H}_{2}}O+4{{e}^{-}}

The separation indicated in the diagram can be either asbestos or some plastic materials. The significance of the separation is to separate cathode and anode compartments and to avoid side reactions from occurring. Few modifications to the electrolytic cells yield the product more efficiently.

For example: If instead carbon (graphite), if mercury is used as cathode efficiency is increased by upto 80 per cent, otherwise it will be arrow 20 per cent. Na+ moving towards cathode mercury gets deposited as Na metal and reacts with Hg to form an amalgam which can then be hydrolysed to form NaOH.

Na(amalgam) + H2O → NaOH + H2 + Hg.


With Acids

When sodium hydroxide is reacted with an acid it forms pure water and salts.

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

With Metals and Oxides

Sodium hydroxide can react with metals at high temperatures to form metal oxides.

4 Fe + 6 NaOH → 2 Fe2O3 + 6 Na + 3 H2

However, some transition metals tend to react vigorously with NaOH. For example Aluminium. can be used to precipitate transition metal hydroxides.

With Acidic Oxides

Sodium hydroxide can also react with acidic oxides. In such reactions, harmful acidic gases are purified. For example,

2NaOH + SO2 → Na2SO3 + H2O

Health Effect and Safety Hazards

  • Sodium hydroxide is a powerful and extremely corrosive alkali it decomposes living tissues.
  • Eye contact of NaOH can cause permanent blindness
  • Skin contact with NaOH is a reason for severe chemical burns
  • Sodium hydroxide solvation is highly exothermic can cause splashing to burn.

Sodium Hydroxide Uses

NaOH is a chemical compound that is used in many instances. Some of its common uses are listed below.

  • Production of soaps.
  • Pulp for paper.
  • Is an important laboratory chemical.
  • Used in production of various other chemicals.
  • Textile industry.
  • Water treatment (converting hard to soft water).
  • Making of glass.