Sodium sulfite (Na2SO3) is a white, water-soluble, crystalline solid with a sulphurous, salty taste. It decomposes when heated. It is generally available in powder, crystalline, and tablet forms.

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Sodium sulfite is yet another dechlorinating agent widely used by utilities. Sodium sulphite is slightly alkaline in nature. Sodium sulfite is a reducing agent và is reported lớn scavenge more oxygen than sodium thiosulfate.

The food industry used sodium sulfite khổng lồ assist in the preservation of the new appearance of food products. In many drugs, it is also an element that helps to preserve their potency & stability. Sodium sulfite has been approved by the FDA as a fresh low regulatory priority animal drug.

Table of Content

What is Sodium Sulfite?

Sodium sulfite is an inorganic salt with the chemical formula Na2SO3. It is an ionic compound containing two sodium cations (Na+) & one sulfite anion (SO32-). A saturated solution of sodium sulfite in water is mildly basic with an approximate p
H value of 9.
Such a solution can undergo crystallisation lớn yield heptahydrate crystals of Na2SO3.


Sodium Sulfite Powder

In its anhydrous size (image provided above), sodium sulfite is a white solid. The primary difference between anhydrous Na2SO3 and its heptahydrate is the relative stability of the anhydrous size towards oxidation. Na2SO3.7H2O is slowly oxidised by atmospheric oxygen, giving rise to the corresponding sulphate.

Structure of Sodium Sulfite- Na2SO3

In a sodium sulfite molecule, there exist two ionic bonds between the sodium cations and the sulfite anion. The structure of a Na2SO3 molecule is illustrated below.


Sodium Sulfite Structure

Each sodium ion holds a charge of +1. On the other hand, the -2 charge on the sulfite ion is delocalized due to lớn resonance, resulting in a partial charge of -⅔ on each oxygen atom. The overall charge on a Na2SO3 molecule is zero.

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Chemical data on Sodium Sulfite

Chemical FormulaNa2SO3
Molar Mass/ Molecular Weight126.043 grams per mole
Density2.633 grams per cubic centimeter (Anhydrous)
Melting Point773K (500o
C) (Anhydrous)
Boiling PointDecomposes

Preparation of Sodium Sulfite

1. In laboratories, sodium sulfite is generally prepared from the reaction between gaseous sulphur dioxide (SO2) & sodium hydroxide (Na
OH). The chemical equation for this reaction is given by

SO2 + 2Na
OH → Na2SO3 + H2O

The depletion of the Na
OH reactant can be detected via the addition of a few drops of concentrated H2SO4, resulting in the liberation of SO2 gas.

2. Industrially, Na2SO3 is produced from the reaction between sulphur dioxide and sodium carbonate solution. Initially, sodium bisulfite (Na
HSO3) is formed. This compound now reacts with sodium carbonate or sodium hydroxide to lớn yield the sodium sulfite product. The reaction can be generalised to:

Na2CO3 + SO2 → Na2SO3 + CO2

Some important physical và chemical properties of sodium sulfite are listed in this subsection.

Physical Properties of Sodium Sulfite

The molar mass of this compound is 126.043 grams per mole.Anhydrous sodium sulfite exists as a white, odourless solid which has a mật độ trùng lặp từ khóa of 2.633 grams per cubic centimetre.The heptahydrate form has a relatively lower density of 1.561 g/cm3.When heated khổng lồ 306.5K (33.4o
C), the heptahydrate undergoes dehydration. The anhydrous khung melts at a temperature of 500 o
C.Sodium sulfite does not have a specific boiling point since it tends khổng lồ decompose at high temperatures.It is moderately soluble in water, its solubility corresponds lớn 27g/100m
L.The crystal structure of anhydrous Na2SO3 is hexagonal whereas the heptahydrate crystals have a monoclinic structure.

Chemical Properties of Sodium Sulfite

Upon liên hệ with strong or weak acids, Na2SO3 undergoes decomposition, liberating gaseous sulphur dioxide.Sodium sulfite reacts with aldehydes khổng lồ yield a bisulfite adduct. However, sulfonic acids are produced from their reaction with ketones.Solutions of sodium sulfite are oxidised by atmospheric oxygen, yielding sodium sulphate.

Uses of Sodium Sulfite

Although its primary applications lie in the pulp & paper industry, Na2SO3 has numerous other applications. A few such applications are listed below.

This compound is often used khổng lồ prevent the discolouration of dried fruits since it can act as a preservative.It is also used in swimming pools lớn decrease the chlorine levels in the water.In boiler systems, this compound acts as an oxygen scavenger khổng lồ protect the system from pitting corrosion. Therefore, the water fed lớn boilers is often treated with sodium sulfite.The textile industry makes extensive use of Na2SO3 for bleaching, dechlorinating and desulfurizing purposes.Sodium sulfite is also used in the process of purifying trinitrotoluene (TNT) in order khổng lồ make it fit for military use.This compound is also an important component in the preparation of sodium thiosulfate.

Sodium Sulfite Health Hazards

Sulfites are compounds containing the sulfite ion, most often in combination with sodium (sodium sulfite) or potassium (potassium sulfite). Sulfites release the irritant gas sulphur dioxide, which acts as a preservative và bleaching agent. As well as occurring naturally in some foods and in the human body, sulfites are added to certain foods to act as a preservative as they inhibit microbial growth, maintain food colour and increase shelf life.

Foods to lớn which sulfites are commonly added include wines, beer và dried fruit. They are also used lớn bleach food starches, such as potato starch và are used in the production of some food packaging materials such as cellophane.

Allergenicity of Sodium Sulfite

It is still unclear why sulfites elicit an allergic reaction in some people but not in others. Sulphur dioxide is an irritant gas & so reflex contraction of the airways has been proposed as one possible mechanism, as the majority of sulfite allergic individuals exhibit asthma-like symptoms.

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Author: Subject: SO2 from Na2SO3
HSO3 synthetises. Exactly I want to make a SO2 generator & I found that is possible from Na2SO3. It would be cheaper for meinstead of using Cu & H2SO4. Here is the link: main question is there anybody did this reaction before? Is it really a good source of SO2?
International Hazard
What could be more straightforward without actually burning sulfur to make it?
H2SO4 is stronger, so the sulphurous acid is liberated.The sulphurous acid levels increase until it exceeds its saturation point và SO2 bubbles out of the solution.It is freed of entrained water by bubbling through the wash bottle full of H2SO4.The mixing of sodium bisulfate & sodium sulfite to lớn make it sounds like an easy route too if you need high purity gas.It"s listed below the other synthesis in your reference.I"m actually kind of surprised they don"t just use sulfur & H2SO4 (heated) to lớn get SO2.I suppose it"s a reaction that might have serious clean-up issues.
Super Administrator
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SO2. Then evaporate to lớn dryness. No need to dry the gas before leading in the solution, so it simply is a matter of making a solution of Na2SO3 inwater và bubbling the produced gas through it. It helps a lot if you make fine bubbles. The SO2 then is absorbed more easily. You could use anaquarium air-stone lớn disperse the gas into small bubbles.The reaction between sulfur and concentrated H2SO4 does not work. I tried this myself và even on strong heating (near 300 C, the acid starts fumingheavily) no appreciable reaction rate could be obtained. The sulfur simply melts và turns red and viscous when it becomes hotter, but I did not get
SO2. On cooling down, the sulfur solidies & you get nice yellow spheres of sulfur. It does not dissolve in the H2SO4.When you want to dry the sodium bisulfite, keep in mind that the material is fairly easily oxidized by air khổng lồ bisulfate. It also fairly easily loses
SO2. The solid is not Na
The art of wondering makes life worth living...Want to wonder? Look at
Radically Dubious
SO2. The solid is not Na
HSO3, albeit does not employ Na2SO3, but sulfur andresults in a stable solution is as follows:First, place burning sulfur in a large vessel until it no longer burns. Remove the sulfur burner.Second, boil distilled water lớn remove any oxygen, then cool in a freezer absent air contact, & then showroom to the large vessel containing SO2.Note, one may consider reversing Steps 1 and 2, lớn limit oxygen contamination.Finally, shake the water/SO2 mix & periodically showroom dry Na
HCO3 (Baking Soda) khổng lồ the vessel. Expected reactions:S + O2 --> SO2SO2 + H2O = H+ + HSO3-H+ + HCO3- --> H2O + CO2 (g)Net:SO2 + H2O + HCO3- --> HSO3- + H2O + CO2 so you now have an aqueous Na
HSO3 as required. Note, it is advised lớn employ a small excess of SO2.I would leave the carbon dioxide in the vessel as a protective layer khổng lồ block out oxygen và also store absent strong light.Note, this process is limited by the kích cỡ of the vessel employed as you will need over 22 liters of SO2 for each mole of product. It does, lớn itsadvantage, by periodic dosing with Na
HCO3, perhaps obviate the SO2 solubility in water issue, as the alkaline Na
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