Sodium Sulfite

What is Sodium sulfite?

Sodium sulfite is an inorganic salt with chemical formula Na2SO3. It is also known as Disodium sulfite or Sodium sulfite anhydrous. It is a sodium salt of sulfurous acid. It is white in color and odorless. It has a slightly salty taste and is moderately toxic. It dissolves in water but is insoluble in ethyl alcohol. Its pH value is 9 -10.5

Sodium sulfite production process –

Laboratory process: Sodium hydroxide solution is reacted with sulfur dioxide gas to give the following:

\(2\,NaOH + SO_{2}\rightarrow Na_{2}SO_{3}+H_{2}O\)

Industrial process: Sulfur dioxide is reacted with a sodium carbonate solution which generates sodium bisulfite. It is converted to sulfite by reacting with sodium carbonate or sodium hydroxide. The overall reaction is as follows:

\(SO_{2} + Na_{2}CO_{3}\rightarrow Na_{2}SO_{3}+CO_{2}\)

Sodium sulfite hazards – This compound can be an irritant to the eyes and skin causing inflammation of eyes and skin. Also, it can be an irritant to the respiratory tract which causes irritation in the throat, nose, and breathing problems.

Properties of Sodium sulfite – Na2SO3

Na2SO3 Sodium sulfite
Molecular Weight/ Molar Mass 126.043 g/mol
Density 2.633 g/cm³
Boiling Point Decomposes
Melting Point 33.4°C

Sodium sulfite structure – Na2SO3

Structure of Sodium sulfite

Na2SO3 Uses (Sodium sulfite)

  • Sodium sulfite is used as an important chemical in the pulp and paper industry.
  • It is used in wastewater treatment plants as an oxygen scavenger agent.
  • It is used in ore flotation.
  • It is used in food preservatives.
  • It is used in the oil recovery process.
  • It is used as a pesticide controller.
  • It is used in manufacturing dyes.
  • It is used in the textile industry.
  • It is used in the production of detergents.
  • It is used in photography in the developing process.

Interesting facts about sodium sulfite:

Na2SO3 has been used as a food preservative for many years. But in the year 1986, the U.S. FDA banned the use of this compound for fixed types of food. This was implemented as one in a hundred people were sensitive to the inorganic salt sodium sulfite which lead to 13 deaths and more than 500 allergic reactions. Therefore the use of sodium sulfite as a preservative on raw vegetables and fruits is now prohibited by the Food and Drug Administration. Also, the processed food items must include a notice on the label if it contains sodium sulfite.

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[IIT-JEE, 2005]