Sulphurous acid is an inorganicdibasic, unstable acid of medium strength. A weak compound is known only in aqueous solutions at a concentration of not more than six percent. When trying to isolate pure sulfuric acid, it decomposes into sulfur oxide (SO2) and water (H2O). For example, under the influence of sulfuric acid (H2SO4) in concentrated form on sodium sulfite (Na2SO3) sulfur dioxide (SO2) is released instead of sulfuric acid. This is what this reaction looks like:
Na2SO3 (sodium sulphite) + H2SO4 (sulfuric acid) = Na2SO4 (sodium sulfate) + SO2 (sulfur dioxide) + H2O (water)
Sulphurous acid solution
When storing it, it is necessary to exclude air access. Otherwise, sulfuric acid, slowly absorbing oxygen (O2), will turn into sulfuric acid.
2H2SO3 (sulfuric acid) + O2 (oxygen) = 2H2SO4 (sulfuric acid)
Sulfuric acid solutions havea specific odor (reminiscent of the smell remaining after the match is lit), the presence of which can be explained by the presence of sulfur dioxide (SO2), chemically not bound by water.
Chemical properties of sulfuric acid
1. Sulfuric acid (formula H2SO3) can be used as a reducing agent or oxidizing agent.
H2SO3 is a good reducing agent. With its help, it is possible to obtain halogenated hydrogen halides out of free halogens. For example:
H2SO3 (sulfuric acid) + Cl2 (chlorine, gas) + H2O (water) = H2SO4 (sulfuric acid) + 2HCl (hydrochloric acid)
But when interacting with strong reducing agents, this acid will act as an oxidizing agent. An example is the reaction of sulfuric acid with hydrogen sulphide:
H2SO3 (sulfuric acid) + 2H2S (hydrogen sulphide) = 3S (sulfur) + 3H2O (water)
2. The chemical compound considered by us forms two types of salts - sulfites (medium) and hydrosulphites (acidic). These salts are reducing agents, as well as (H2SO3) sulfurous acid. When they are oxidized, salts of sulfuric acid are formed. When calcining sulfites of active metals, sulfates and sulphides are formed. This is a self-oxidation-self-healing reaction. For example:
4Na2SO3 (sodium sulfite) = Na2S (sodium sulphide) + 3Na2SO4 (sodium sulphate)
Sodium and potassium sulfites (Na2SO3 and K2SO3)They are used in dyeing fabrics in the textile industry, in bleaching metals, and in photography. Calcium hydrosulfite (Ca (HSO3) 2), which exists only in solution, is used for the processing of wood material in a special sulphite pulp. From it, then make paper.
The use of sulfuric acid
Sulphurous acid is used:
- for discoloration of wool, silk, wood pulp, paper and other similar substances that do not withstand bleaching by means of stronger oxidants (eg chlorine);
- as a preservative and antiseptic, for example, to prevent fermentation of grain when obtaining starch or to prevent the fermentation process in barrels of wine;
- for the preservation of products, for example, when preserving vegetables and fruits;
- in the processing of wood chips into celluloseSulphite, from which paper is then obtained. In this case, a solution of calcium hydrosulfite (Ca (HSO3) 2) is used, which dissolves lignin, a special substance that binds cellulose fibers.
Sulphurous acid: preparation
This acid can be obtained by dissolving sulfur dioxide gas (SO2) in water (H2O). You will need sulfuric acid in concentrated form (H2SO4), copper (Cu) and a test tube. Algorithm of actions:
1. Carefully pour concentrated sulfuric acid into the tube and then place a piece of copper there. Heat. The following reaction occurs:
Cu (copper) + 2H2SO4 (sulfuric acid) = CuSO4 (sulfur sulphate) + SO2 (sour gas) + H2O (water)
2. The flow of sulfur dioxide should be sent to a test tube with water. When it dissolves, a chemical reaction with water occurs partially, resulting in the formation of sulfuric acid:
SO2 (sour gas) + H2O (water) = H2SO3
So, by passing sulfur dioxide through water, you canto get sulphurous acid. It should be noted that this gas has an irritant effect on the airway envelopes, can cause their inflammation, as well as loss of appetite. With prolonged inhalation, loss of consciousness is possible. Handle this gas with extreme caution and care.