Chlorous Acid | Preparation, Properties, Uses, Hazards |

Chlorous Acid.

Chlorous Acid | Preparation, Properties, Uses, Hazards |

It is an inorganic compound having molecular formula HClO2 .It has one proton Hattached to chlorite anion ClO2 .It is oxyacid of chlorine where the oxidation state of Cl is 3+. It is also known as hydrochlorous acid.

Chlorous Acid.

Lewis Structure of Chlorous Acid.

Electronic Configuration.
Hydrogen 1s1.
Oxygen [He] 2s2p4.

Chlorine [Ne] 3s2 3p5.

Lewis Structure of Chlorous Acid.

Molecular Geometry.

Central the metal atom is Cl containing 7 valance electron. The one 3s and three 3p orbital of chlorine intermix and redistribute energy to form new four equivalent hybrid orbital so according to VSEPR theory hybridization of Chlorous Acid is sp3.
Molecular Geometry.

ClO2– ion has an angular shape with a bond angle of about 111°.

ClO2 - ion has angular shape with a bond angle of about 111°.


It is a weak acid. Its pKa value is 1.96. The pure substance of chlorous acid is unstable so the conjugate base of such acid is chlorite ion which is stable. It’s acid dissociation constant K a is 1.2 × 10-2.

Preparation of Chlorous Acid.

It is obtained by treating a suspension of barium chlorite with dil. Sulfuric acid and filtering of the precipitates of BaSO4 .

Physical Properties of Chlorous Acid.

  1. It is a colorless liquid when isolated without a characteristic smell.

  2. Its molecular weight is 68.456 g/mol.

  3. It has no net charge.

Chemical Properties of Chlorous Acid.

  1. The freshly the prepared solution of acid is colorless but soon decomposes to ClO2yellow solution. It gives a violet color with FeSO4.

  2. It is powerful oxidizing agent.

  3. It liberates iodine from an iodide.

  4. The acid undergoes auto-oxidation/reduction at ordinary temperature and changes into HClO and HClO3.

  5. HClO2 disproportionation to hypochlorous acid(Cl1+ ) and chloric acid (Cl5+ ). Reduction of Cl3+ to Cl1+  and oxidation of Cl3+  to Cl5+.

Chlorous Acid Uses.

  1. Chlorous acid is reported as an effective bleaching agent because of its use for the removal of lignin and noncarbohydrate components from wood pulp without action on carbohydrates.

  2. Sodium salt of chlorite ion is used in some industrial processes as the production of chlorine dioxide. It can be prepared by the reaction of ClO2 with aqueous NaOH.

  3. Calcium chlorite is a strong oxidizing agent. It can be prepared by the reaction of chlorous acid with calcium carbonate.

    It is white granular solid crystallizes as the hexahydrate. It is noncombustible and accelerates the burning of combustible materials. It is decomposed by water to form calcium hydroxide and chlorine dioxide an explosive oxidizing gas.

Chlorous Acid Hazards.

Chlorous acid is an unstable compound and strong oxidizing agent so it is harmful if swallowed or inhaled, cause severe damages and irritation in case of contact with skin and eyes as it contains chlorine. If acid comes in to contact with skin it should be washed with cold water using a non-abrasive soap.
Sodium chlorite is corrosive for equipment. So it is necessary to use ceramic, plastic or special steel equipment for the bleaching process.

Author, Kaiser Saleem

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