What Is Sodium Metabisulfite Definition Formula Reactions and Uses
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:
[Image will be Uploaded Soon]
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.
FAQs on Sodium Metabisulfite Structure Properties and Applications
1. What is sodium metabisulfite?
Sodium metabisulfite is an inorganic compound with the chemical formula Na2S2O5 that acts as a strong reducing agent and preservative. It is a white crystalline powder that releases sulfur dioxide (SO2) when dissolved in water or treated with acids. In aqueous solution, it forms bisulfite ions (HSO3-), which are responsible for its antioxidant and antimicrobial properties. It is widely used in food preservation, water treatment, and laboratory chemistry.
2. What is the chemical formula and molar mass of sodium metabisulfite?
The chemical formula of sodium metabisulfite is Na2S2O5 and its molar mass is approximately 190.10 g·mol-1. The molar mass is calculated as follows:
- Na: 2 × 22.99 = 45.98 g·mol-1
- S: 2 × 32.06 = 64.12 g·mol-1
- O: 5 × 16.00 = 80.00 g·mol-1
3. How is sodium metabisulfite prepared?
Sodium metabisulfite is prepared by passing sulfur dioxide gas through a concentrated solution of sodium carbonate. The balanced chemical reaction is:
2Na2CO3(aq) + 2SO2(g) → Na2S2O5(aq) + 2CO2(g).
- Sulfur dioxide reacts with sodium carbonate to form sodium sulfite first.
- Further reaction with SO2 leads to formation of sodium metabisulfite.
- The product is then crystallized and dried.
4. What happens when sodium metabisulfite reacts with water?
When sodium metabisulfite dissolves in water, it forms sodium bisulfite in equilibrium. The reaction is:
Na2S2O5(s) + H2O(l) → 2NaHSO3(aq).
- The solution becomes mildly acidic.
- Bisulfite ions (HSO3-) act as reducing agents.
- It can release SO2 in acidic conditions.
5. Is sodium metabisulfite an oxidizing or reducing agent?
Sodium metabisulfite is primarily a reducing agent because it donates electrons and gets oxidized to sulfate. For example, it reduces iodine to iodide:
Na2S2O5(aq) + I2(aq) + H2O(l) → Na2SO4(aq) + 2HI(aq) + SO2(aq).
- Sulfur in +4 oxidation state is oxidized to +6 in sulfate.
- This property is used in titrations and bleaching processes.
6. What are the common uses of sodium metabisulfite?
Sodium metabisulfite is widely used as a preservative, antioxidant, and disinfectant in various industries. Common uses include:
- Food industry: Prevents oxidation and browning in dried fruits and juices.
- Water treatment: Removes excess chlorine.
- Laboratory chemistry: Acts as a reducing agent in redox reactions.
- Pharmaceuticals: Prevents oxidation of drugs.
7. What is the oxidation state of sulfur in sodium metabisulfite?
The oxidation state of sulfur in sodium metabisulfite (Na2S2O5) is +4 on average. This can be calculated by assigning oxidation numbers:
- Na = +1 each (total +2)
- O = −2 each (5 × −2 = −10)
2(+1) + 2x − 10 = 0 → 2x − 8 = 0 → x = +4. This +4 state explains its tendency to oxidize to sulfate (+6).
8. What is the difference between sodium sulfite and sodium metabisulfite?
The main difference is that sodium sulfite has the formula Na2SO3, while sodium metabisulfite has the formula Na2S2O5. Key differences include:
- Composition: Metabisulfite contains two sulfur atoms; sulfite contains one.
- Hydrolysis: Na2S2O5 forms 2NaHSO3 in water.
- SO2 release: Metabisulfite releases sulfur dioxide more readily in acidic conditions.
9. How does sodium metabisulfite react with acids?
Sodium metabisulfite reacts with acids to release sulfur dioxide gas. A typical balanced reaction with hydrochloric acid is:
Na2S2O5(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + 2SO2(g).
- The reaction produces pungent SO2 gas.
- This confirms the presence of sulfite or metabisulfite ions.
10. Is sodium metabisulfite acidic or basic in solution?
Sodium metabisulfite forms a mildly acidic solution in water due to formation of bisulfite ions. The hydrolysis reaction is:
Na2S2O5(s) + H2O(l) → 2NaHSO3(aq).
- HSO3- partially ionizes to release H+.
- The pH of the solution is typically below 7.
