Sodium Metabisulfite

Introduction

Sodium Metabisulfite has the chemical formula Na2S2O5  and its molecular mass is 190.107g/mol. It is a sulfur-containing ionic compound of sodium. Sodium has a positive charge while metabisulfite (S2O52-) has a negative charge. It is called Metabisulfite due to the presence of two S atoms. Meta term refers to the direct bond present between two S atoms. It is a well-known antioxidant being used in pharmaceuticals. It is white in color and solid powder form.

In this article, We will discuss the structure, chemical and physical properties, uses of Sodium metabisulfite.

Structure

We know that the chemical formula of Sodium Metabisulfite is Na2S2O5. It has two sodium atoms, two sulfur, and five oxygen atoms. Na+  is balancing the charge in the structure. Two sulfur atoms are directly attached to each other through a single bond. A sulfur atom which has 3 Oxygen atoms, has an oxidation state of +5.  Another sulfur atom has an oxidation number of +3. The structure of this compound is shown below:

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Preparation

There are a number of methods available to synthesize sodium metabisulphite. One of them is by using Sodium sulfite and sodium bisulfite solution. Sulfur Dioxide is added to this solution. It maintains the pH of the solution. NaOH is added to the above solution.

In the solution, There is an equilibrium between the ions as shown below:

2HSO32- ⇌ S2O2-5 + H2O

When NaOH is added to the above solution, free Na+  ions form with bisulfite ions and Sodium metabisulfite is achieved. It enhances the crystallization process per cycle and more yield of Sodium Metabisulfite is achieved.

Properties

Physical Properties

• It is white in color, solid, and in powder form.

• It has a similar odor to Sulfur dioxide.

• The molar mass of sodium metabisulfite is 190.107 g/mol.

• It has a melting point of 180⁰C,  but it decomposes around 150⁰C.

• On boiling, It decomposes readily.

Chemical Properties

• sodium metabisulfite pH is maintained at 4.6 while preparing the solution. So, it is acidic in nature.

• It is non-combustible in nature. When heated at high temperature, it releases toxic flames of oxides of sulfur

• When it is mixed in water, it releases sulfur dioxide. It is very harmful to the lungs. It has a pungent strong smell.

• When it is treated with strong acids, it releases SO2. The reaction is shown below:

2HCL + Na2S2O5 ⇌  2SO2 + 2NaCl + H2O

Sodium Metabisulfite Uses

• It is the most commonly used preservative for baked goods, wines, jams, cookies.

• It acts as a reducing agent in the dough, it helps in making batter softer, easier to knead.

• It is a well-known antioxidant used in pharmaceuticals.

• It is helpful in tests of sickle cell anemia.

• It is used in industries as a corrosion inhibitor because it is an oxygen scavenger.

• It is used in wastewater treatment as it is a good reducing agent.

• It is used as a sanitizing ingredient, to clean the tools of winemaking.

Did You Know?

It is extensively used in makeup and skincare products. It has antioxidant properties, so it is added to skin care products to increase their shelf life. It is safer to use on the skin. Because of its disinfectant properties, it is used in sanitizers. Sanitizers are in high demand nowadays because of the Corona pandemic. So, the usage of sodium metabisulfite is also increased.