Obtaining oxides during the combustion of simple substances. Methods for obtaining oxides

1. Oxidation of simple substances with oxygen (combustion of simple substances):

2 mg + O 2 = 2MgO

4P + 5O 2 = 2P 2 O 5 .

The method is not applicable for the production of alkali metal oxides, since when oxidized, alkali metals usually give not oxides, but peroxides (Na 2 O 2 , K 2 O 2 ) .

Noble metals are not oxidized by atmospheric oxygen, for example, BUTu, BUTg, Rt.

2. Oxidation of complex substances (salts of certain acids and hydrogen compounds of non-metals):

2ZnS + 3O 2 = 2ZnO + 2SO 2

2 H 2 S+3O 2 = 2SO 2 + 2 H 2 O

3.Decomposition upon heating of hydroxides (bases and oxygen-containing acids):

FROMu(HE) 2 FROMuO + H 2 O

H 2 SO 3 SO 2 + H 2 O

This method cannot be used to obtain oxides of alkali metals, since the decomposition of alkalis occurs at too high temperatures.

4.Decomposition of some salts of oxygen-containing acids:

CaCO 3 CaO + CO 2

2Rb(NO 3 ) 2 2RbO + 4NO 2 + O 2

It should be borne in mind that alkali metal salts do not decompose when heated to form oxides.

1.1.7. Applications of oxides.

A number of natural minerals are oxides (see Table 7) and are used as ore raw materials to obtain the corresponding metals.

For example:

Bauxite A1 2 O 3 · nH 2 O.

HematiteFe 2 O 3 .

MagnetiteFeO ·Fe 2 O 3 .

CassiteriteSNO 2 .

Pyrolusite Mno 2 .

Rutile TiO 2 .

mineral corundum (A1 2 O 3 ) having great hardness, is used as an abrasive material. Its transparent, red and blue colored crystals are precious stones - ruby ​​and sapphire.

Quicklime (CaO) obtained by roasting limestone (CaCO 3 ) , is widely used in construction, agriculture and as a reagent for drilling fluids.

iron oxides (Fe 2 O 3 , Fe 3 O 4 ) used in drilling oil and gas wells as weighting agents and hydrogen sulfide neutralizing agents.

Silicon(IV) oxide (SiO 2 ) in the form of quartz sand, it is widely used for the production of glass, cement and enamels, for sandblasting the surface of metals, for hydrosandblasting perforation and hydraulic fracturing in oil and gas wells. In the form of the smallest spherical particles (aerosol), it is used as an effective defoamer for drilling fluids and as a filler in the production of rubber products (white rubber).

A number of oxides (A1 2 O 3 , Cr 2 O 3 , V 2 O 5 , FROMuO,NO) are used as catalysts in modern chemical industries.

Being one of the main combustion products of coal, oil and oil products, carbon dioxide (CO 2 ), when injected into productive formations, enhances their oil recovery. CO 2 is also used to fill fire extinguishers and carbonate drinks.

The oxides formed during the violation of the combustion regimes of fuel (NO, CO) or during the combustion of sulfurous fuel (SO 2) are products that pollute the atmosphere. Modern production, as well as transport, provides for strict control over the content of such oxides and their neutralization,

Oxides of nitrogen (NO, NO 2) and sulfur (SO 2 , SO 3) are intermediate products in large-scale production of nitric (HNO 3) and sulfuric (H 2 SO 4) acids.

Oxides of chromium (Cr 2 O 3) and lead (2PbO PbO 2 - minium) are used for the production of anticorrosive paint compositions.

Today we begin our acquaintance with the most important classes of inorganic compounds. Inorganic substances are divided by composition, as you already know, into simple and complex.

Complex inorganic substances are divided into four classes: oxides, acids, bases, salts. We start with the oxide class.

OXIDES

oxides - these are complex substances consisting of two chemical elements, one of which is oxygen, with a valence equal to 2. Only one chemical element - fluorine, combining with oxygen, forms not an oxide, but oxygen fluoride OF 2.
They are called simply - "oxide + element name" (see table). If the valence of a chemical element is variable, then it is indicated by a Roman numeral enclosed in parentheses after the name of the chemical element.

Classification of oxides

All oxides can be divided into two groups: salt-forming (basic, acidic, amphoteric) and non-salt-forming or indifferent.

1). Basic oxides are oxides that correspond to bases. The main oxides are oxides metals 1 and 2 groups, as well as metals side subgroups with valence I and II (except ZnO - zinc oxide and BeO – beryllium oxide):

2). Acid oxides are oxides to which acids correspond. Acid oxides are non-metal oxides (except for non-salt-forming - indifferent), as well as metal oxides side subgroups with valency from V before VII (For example, CrO 3 is chromium (VI) oxide, Mn 2 O 7 is manganese (VII) oxide):

3). Amphoteric oxides are oxides, which correspond to bases and acids. These include metal oxides main and secondary subgroups with valence III , sometimes IV , as well as zinc and beryllium (For example, BeO, ZnO, Al 2 O 3, Cr 2 O 3).

4). Non-salt-forming oxides are oxides that are indifferent to acids and bases. These include non-metal oxides with valence I and II (For example, N 2 O, NO, CO).

Conclusion: the nature of the properties of oxides primarily depends on the valency of the element.

For example, chromium oxides:

CrO(II- main);

Cr 2 O 3 (III- amphoteric);

CrO 3 (VII- acid).

Classification of oxides

(by solubility in water)

Complete the tasks:

1. Write down separately the chemical formulas of salt-forming acidic and basic oxides.

NaOH, AlCl 3 , K 2 O, H 2 SO 4 , SO 3 , P 2 O 5 , HNO 3 , CaO, CO.

2. Substances are given : CaO, NaOH, CO 2 , H 2 SO 3 , CaCl 2 , FeCl 3 , Zn(OH) 2 , N 2 O 5 , Al 2 O 3 , Ca(OH) 2 , CO 2 , N 2 O, FeO, SO 3 , Na 2 SO 4 , ZnO, CaCO 3 , Mn 2 O 7 , CuO, KOH, CO, Fe(OH) 3

Obtaining oxides

Simulator "Interaction of oxygen with simple substances"

Physical properties of oxides

At room temperature, most oxides are solids (CaO, Fe 2 O 3, etc.), some are liquids (H 2 O, Cl 2 O 7, etc.) and gases (NO, SO 2, etc.).

Chemical properties of oxides

Application of oxides

Some oxides do not dissolve in water, but many react with water to combine:

SO 3 + H 2 O \u003d H 2 SO 4

CaO + H 2 O = Ca( Oh) 2

The result is often very desirable and useful compounds. For example, H 2 SO 4 is sulfuric acid, Ca (OH) 2 is slaked lime, etc.

If oxides are insoluble in water, then people skillfully use this property as well. For example, zinc oxide ZnO is a white substance, therefore it is used to prepare white oil paint (zinc white). Since ZnO is practically insoluble in water, any surface can be painted with zinc white, including those that are exposed to atmospheric precipitation. Insolubility and non-toxicity make it possible to use this oxide in the manufacture of cosmetic creams and powders. Pharmacists make it an astringent and drying powder for external use.

Titanium oxide (IV) - TiO 2 has the same valuable properties. It also has a beautiful white color and is used to make titanium white. TiO 2 is insoluble not only in water, but also in acids; therefore, coatings made of this oxide are particularly stable. This oxide is added to plastic to give it a white color. It is part of the enamels for metal and ceramic utensils.

Chromium oxide (III) - Cr 2 O 3 - very strong crystals of dark green color, insoluble in water. Cr 2 O 3 is used as a pigment (paint) in the manufacture of decorative green glass and ceramics. The well-known GOI paste (short for the name “State Optical Institute”) is used for grinding and polishing optics, metal products in jewelry.

Tasks for fixing

1. Write down separately the chemical formulas of salt-forming acidic and basic oxides.

NaOH, AlCl 3 , K 2 O, H 2 SO 4 , SO 3 , P 2 O 5 , HNO 3 , CaO, CO.

2. Substances are given : CaO, NaOH, CO 2 , H 2 SO 3 , CaCl 2 , FeCl 3 , Zn(OH) 2 , N 2 O 5 , Al 2 O 3 , Ca(OH) 2 , CO 2 , N 2 O, FeO, SO 3 , Na 2 SO 4 , ZnO, CaCO 3 , Mn 2 O 7 , CuO, KOH, CO, Fe(OH) 3

Select from the list: basic oxides, acidic oxides, indifferent oxides, amphoteric oxides and name them.

3. Finish UCR, indicate the type of reaction, name the reaction products

Na 2 O + H 2 O =

N 2 O 5 + H 2 O =

CaO + HNO 3 =

NaOH + P 2 O 5 \u003d

K 2 O + CO 2 \u003d

Cu (OH) 2 \u003d? +?

4. Carry out the transformations according to the scheme:

1) K → K 2 O → KOH → K 2 SO 4

2) S → SO 2 → H 2 SO 3 → Na 2 SO 3

3) P → P 2 O 5 → H 3 PO 4 → K 3 PO 4

The substances that form the basis of our physical world are composed of different types of chemical elements. Four of them are the most common. These are hydrogen, carbon, nitrogen and oxygen. The last element can bind with particles of metals or non-metals and form binary compounds - oxides. In our article, we will study the most important methods for obtaining oxides in the laboratory and industry. We also consider their basic physical and chemical properties.

State of aggregation

Oxides, or oxides, exist in three states: gaseous, liquid and solid. For example, the first group includes such well-known and widespread compounds in nature as carbon dioxide - CO 2, carbon monoxide - CO, sulfur dioxide - SO 2 and others. In the liquid phase, there are such oxides as water - H 2 O, sulfuric anhydride - SO 3, nitric oxide - N 2 O 3. Obtaining oxides, named by us, can be carried out in the laboratory, however, such of them, as well as sulfur trioxide, are also mined in industry. This is due to the use of these compounds in the technological cycles of iron smelting and sulfate acid production. Carbon monoxide is used to reduce iron from ore, and sulfuric anhydride is dissolved in sulfate acid and oleum is mined.

Classification of oxides

There are several types of oxygen-containing substances, consisting of two elements. The chemical properties and methods for obtaining oxides will depend on which of the listed groups the substance belongs to. carbon is obtained by direct combination of carbon with oxygen, carrying out a hard oxidation reaction. Carbon dioxide can also be isolated in the process of exchange and strong inorganic acids:

HCl + Na 2 CO 3 \u003d 2NaCl + H 2 O + CO 2

What reaction is the hallmark of acid oxides? This is their interaction with alkalis:

SO 2 + 2NaOH → Na 2 SO 3 + H 2 O

Amphoteric and non-salt-forming oxides

Indifferent oxides, such as CO or N 2 O, are not capable of reactions leading to the appearance of salts. On the other hand, most acidic oxides can react with water to form acids. However, this is not possible for silicon oxide. It is advisable to obtain silicate acid indirectly: from silicates that react with strong acids. Amphoteric will be such binary compounds with oxygen that are capable of reactions with both alkalis and acids. We include the following compounds in this group - these are the known oxides of aluminum and zinc.

Production of sulfur oxides

In its compounds with oxygen, sulfur exhibits different valencies. So, in sulfur dioxide, the formula of which is SO 2, it is tetravalent. In the laboratory, sulfur dioxide is produced in the reaction between sulfate acid and sodium hydrosulfite, the equation of which is

NaHSO 3 + H 2 SO 4 → NaHSO 4 + SO 2 + H 2 O

Another way to extract SO 2 is a redox process between copper and high concentration sulfate acid. The third laboratory method for obtaining sulfur oxides is the combustion under the hood of a sample of a simple sulfur substance:

Cu + 2H 2 SO 4 \u003d CuSO 4 + SO 2 + 2H 2 O

In industry, sulfur dioxide can be obtained by burning sulfur-containing minerals zinc or lead, as well as by burning pyrite FeS 2. The sulfur dioxide obtained by this method is used for the extraction of sulfur trioxide SO 3 and further - sulfate acid. Sulfur dioxide with other substances behaves like an oxide with acidic features. For example, its interaction with water leads to the formation of sulfite acid H 2 SO 3:

SO 2 + H 2 O \u003d H 2 SO 3

This reaction is reversible. The degree of acid dissociation is low, so the compound is classified as a weak electrolyte, and sulfurous acid itself can exist only in an aqueous solution. Sulfur dioxide molecules are always present in it, which give the substance a pungent odor. The reacting mixture is in a state of equal concentration of reactants and products, which can be shifted by changing the conditions. So, when alkali is added to a solution, the reaction will proceed from left to right. In the case of removing sulfur dioxide from the reaction sphere by heating or blowing through a mixture of gaseous nitrogen, the dynamic equilibrium will shift to the left.

Sulfuric anhydride

We continue to consider the properties and methods for obtaining sulfur oxides. If sulfur dioxide is burned, the result is an oxide in which sulfur has an oxidation state of +6. It's sulfur trioxide. The compound is in the liquid phase, quickly hardens in the form of crystals at temperatures below 16 °C. A crystalline substance can be represented by several allotropic modifications that differ in the structure of the crystal lattice and melting points. Sulfuric anhydride exhibits the properties of a reducing agent. Interacting with water, it forms an aerosol of sulfate acid, therefore, in industry, H 2 SO 4 is mined by dissolving sulfuric anhydride in concentrated oleum. As a result, oleum is formed. By adding water to it, a solution of sulfuric acid is obtained.

Basic oxides

Having studied the properties and production of sulfur oxides belonging to the group of acidic binary compounds with oxygen, we will consider oxygen compounds of metal elements.

Basic oxides can be determined by such a feature as the presence in the composition of the molecules of metal particles of the main subgroups of the first or second groups of the periodic system. They are classified as alkaline or alkaline earth. For example, sodium oxide - Na 2 O can react with water, resulting in the formation of chemically aggressive hydroxides - alkalis. However, the main chemical property of basic oxides is the interaction with organic or inorganic acids. It goes with the formation of salt and water. If hydrochloric acid is added to white powdered copper oxide, we will find a bluish-green solution of copper chloride:

CuO + 2HCl \u003d CuCl 2 + H 2 O

Heating solid insoluble hydroxides is another important way to obtain basic oxides:

Ca(OH) 2 → CaO + H 2 O

Conditions: 520-580°C.

In our article, we examined the most important properties of binary compounds with oxygen, as well as methods for obtaining oxides in the laboratory and industry.

Properties of oxides

oxides- these are complex chemicals, which are chemical compounds of simple elements with oxygen. They are salt-forming and not forming salts. In this case, salt-forming are of 3 types: main(from the word "foundation"), acidic and amphoteric.
An example of oxides that do not form salts can be: NO (nitric oxide) - is a colorless gas, odorless. It is formed during a thunderstorm in the atmosphere. CO (carbon monoxide) is an odorless gas produced by the combustion of coal. It is commonly referred to as carbon monoxide. There are other oxides that do not form salts. Now let's take a closer look at each type of salt-forming oxides.

Basic oxides

Basic oxides- These are complex chemical substances related to oxides that form salts by chemical reaction with acids or acid oxides and do not react with bases or basic oxides. For example, the main ones are:
K 2 O (potassium oxide), CaO (calcium oxide), FeO (2-valent iron oxide).

Consider chemical properties of oxides by examples

1. Interaction with water:
- interaction with water to form a base (or alkali)

CaO + H 2 O → Ca (OH) 2 (a well-known lime slaking reaction, while a large amount of heat is released!)

2. Interaction with acids:
- interaction with acid to form salt and water (solution of salt in water)

CaO + H 2 SO 4 → CaSO 4 + H 2 O (Crystals of this substance CaSO 4 are known to everyone under the name "gypsum").

3. Interaction with acid oxides: salt formation

CaO + CO 2 → CaCO 3 (This substance is known to everyone - ordinary chalk!)

Acid oxides

Acid oxides- these are complex chemicals related to oxides that form salts when chemically interacting with bases or basic oxides and do not interact with acidic oxides.

Examples of acidic oxides are:

CO 2 (well-known carbon dioxide), P 2 O 5 - phosphorus oxide(produced by combustion in air) white phosphorus), SO 3 - sulfur trioxide - this substance is used to obtain sulfuric acid.

Chemical reaction with water

CO 2 +H 2 O→ H 2 CO 3 is a substance - carbonic acid - one of the weak acids, it is added to sparkling water for "bubbles" of gas. As the temperature rises, the solubility of the gas in water decreases, and its excess comes out in the form of bubbles.

Reaction with alkalis (bases):

CO 2 +2NaOH→ Na 2 CO 3 +H 2 O- the resulting substance (salt) is widely used in the economy. Its name - soda ash or washing soda - is an excellent detergent for burnt pans, grease, burns. I do not recommend working with bare hands!

Reaction with basic oxides:

CO 2 + MgO → MgCO 3 - received salt - magnesium carbonate - also called "bitter salt".

Amphoteric oxides

Amphoteric oxides- these are complex chemicals, also related to oxides, which form salts during chemical interaction with acids (or acid oxides) and bases (or basic oxides). The most common use of the word "amphoteric" in our case refers to metal oxides.

An example amphoteric oxides can be:

ZnO - zinc oxide (white powder, often used in medicine for the manufacture of masks and creams), Al 2 O 3 - aluminum oxide (also called "alumina").

The chemical properties of amphoteric oxides are unique in that they can enter into chemical reactions corresponding to both bases and acids. For example:

Reaction with acid oxide:

ZnO + H 2 CO 3 → ZnCO 3 + H 2 O - The resulting substance is a solution of "zinc carbonate" salt in water.

Reaction with bases:

ZnO + 2NaOH → Na 2 ZnO 2 + H 2 O - the resulting substance is a double salt of sodium and zinc.

Obtaining oxides

Obtaining oxides produced in various ways. This can happen in physical and chemical ways. The simplest way is the chemical interaction of simple elements with oxygen. For example, the result of a combustion process or one of the products of this chemical reaction are oxides. For example, if a red-hot iron rod, and not only iron (you can take zinc Zn, tin Sn, lead Pb, copper Cu, - in general, what is at hand) is placed in a flask with oxygen, then a chemical oxidation reaction of iron will occur, which accompanied by a bright flash and sparks. The reaction product will be black iron oxide FeO powder:

2Fe+O 2 → 2FeO

Completely similar chemical reactions with other metals and non-metals. Zinc burns in oxygen to form zinc oxide

2Zn+O 2 → 2ZnO

The combustion of coal is accompanied by the formation of two oxides at once: carbon monoxide and carbon dioxide.

2C+O 2 → 2CO - the formation of carbon monoxide.

C + O 2 → CO 2 - the formation of carbon dioxide. This gas is formed if there is more than enough oxygen, that is, in any case, the reaction proceeds first with the formation of carbon monoxide, and then the carbon monoxide is oxidized, turning into carbon dioxide.

Obtaining oxides can be done in another way - by decomposition chemical reaction. For example, to obtain iron oxide or aluminum oxide, it is necessary to calcinate the corresponding bases of these metals :

Fe(OH) 2 → FeO+H 2 O

Solid aluminum oxide - mineral corundum Iron(III) oxide. The surface of the planet Mars has a reddish-orange color due to the presence of iron (III) oxide in the soil. Solid aluminum oxide - corundum

2Al(OH) 3 → Al 2 O 3 + 3H 2 O,
as well as in the decomposition of individual acids:

H 2 CO 3 → H 2 O + CO 2 - decomposition of carbonic acid

H 2 SO 3 → H 2 O + SO 2 - decomposition of sulfurous acid

Obtaining oxides can be made from metal salts with strong heating:

CaCO 3 → CaO + CO 2 - calcium oxide (or quicklime) and carbon dioxide are obtained by calcining chalk.

2Cu(NO 3) 2 → 2CuO + 4NO 2 + O 2 - in this decomposition reaction, two oxides are obtained at once: copper CuO (black) and nitrogen NO 2 (it is also called brown gas because of its really brown color).

Another way in which oxides can be obtained is redox reactions

Cu + 4HNO 3 (conc.) → Cu(NO 3) 2 + 2NO 2 + 2H 2 O

S + 2H 2 SO 4 (conc.) → 3SO 2 + 2H 2 O

Chlorine oxides

The following are known chlorine oxides: Cl 2 O, ClO 2 , Cl 2 O 6 , Cl 2 O 7 . All of them, with the exception of Cl 2 O 7 , are yellow or orange in color and are not stable, especially ClO 2 , Cl 2 O 6 . All chlorine oxides explosive and are very strong oxidizers.

Reacting with water, they form the corresponding oxygen-containing and chlorine-containing acids :

So, Cl 2 O - acid chlorine oxide hypochlorous acid.

Cl 2 O + H 2 O → 2HClO - Hypochlorous acid

ClO 2 - acid chlorine oxide hypochlorous and hypochlorous acids, since in a chemical reaction with water it forms two of these acids at once:

ClO 2 + H 2 O → HClO 2 + HClO 3

Cl 2 O 6 - too acid chlorine oxide chloric and perchloric acids:

Cl 2 O 6 + H 2 O → HClO 3 + HClO 4

And finally, Cl 2 O 7 - a colorless liquid - acid chlorine oxide perchloric acid:

Cl 2 O 7 + H 2 O → 2HClO 4

nitrogen oxides

Nitrogen is a gas that forms 5 different compounds with oxygen - 5 nitrogen oxides. Namely:

N 2 O - nitrogen hemioxide. Its other name is known in medicine under the name laughing gas or nitrous oxide- It is colorless sweetish and pleasant to the taste on the gas.
-NO- nitrogen monoxide A colorless, odorless, tasteless gas.
- N 2 O 3 - nitrous anhydride- colorless crystalline substance
- NO 2 - nitrogen dioxide. Its other name is brown gas- the gas really has a brown color
- N 2 O 5 - nitric anhydride- blue liquid boiling at a temperature of 3.5 0 C

Of all these listed nitrogen compounds, NO - nitrogen monoxide and NO 2 - nitrogen dioxide are of the greatest interest in industry. nitrogen monoxide(NO) and nitrous oxide N 2 O does not react with either water or alkalis. (N 2 O 3) when reacting with water, forms a weak and unstable nitrous acid HNO 2, which gradually turns into a more stable chemical substance in air nitric acid Consider some chemical properties of nitrogen oxides:

Reaction with water:

2NO 2 + H 2 O → HNO 3 + HNO 2 - 2 acids are formed at once: nitric acid HNO 3 and nitrous acid.

Reaction with alkali:

2NO 2 + 2NaOH → NaNO 3 + NaNO 2 + H 2 O - two salts are formed: sodium nitrate NaNO 3 (or sodium nitrate) and sodium nitrite (salt of nitrous acid).

Reaction with salts:

2NO 2 + Na 2 CO 3 → NaNO 3 + NaNO 2 + CO 2 - two salts are formed: sodium nitrate and sodium nitrite, and carbon dioxide is released.

Obtain nitrogen dioxide (NO 2) from nitrogen monoxide (NO) using the chemical reaction of the compound c oxygen :

2NO + O 2 → 2NO 2

iron oxides

Iron forms two oxide: FeO- iron oxide(2-valent) - black powder, which is obtained by reduction iron oxide(3-valent) carbon monoxide by the following chemical reaction:

Fe 2 O 3 + CO → 2FeO + CO 2

This basic oxide readily reacts with acids. It has reducing properties and is rapidly oxidized to iron oxide(3-valent).

4FeO +O 2 → 2Fe 2 O 3

iron oxide(3-valent) - red-brown powder (hematite), which has amphoteric properties (it can interact with both acids and alkalis). But the acidic properties of this oxide are so weakly expressed that it is most often used as basic oxide.

There are also so-called mixed iron oxide Fe 3 O 4 . It is formed during the combustion of iron, conducts electricity well and has magnetic properties (it is called magnetic iron ore or magnetite). If iron burns out, then as a result of the combustion reaction, scale is formed, consisting of two oxides at once: iron oxide(III) and (II) valence.

Sulfur oxide

Sulfur oxide SO 2 - or sulphur dioxide refers to acid oxides, but it does not form an acid, although it dissolves perfectly in water - 40 liters of sulfur oxide in 1 liter of water (for the convenience of compiling chemical equations, such a solution is called sulfuric acid).

Under normal circumstances, it is a colorless gas with a pungent and suffocating smell of burnt sulfur. At a temperature of only -10 0 C, it can be transferred to a liquid state.

In the presence of a catalyst -vanadium oxide (V 2 O 5) sulfur oxide takes on oxygen and turns into sulfur trioxide

2SO 2 + O 2 → 2SO 3

dissolved in water sulphur dioxide- sulfur oxide SO 2 - oxidizes very slowly, as a result of which the solution itself turns into sulfuric acid

If a sulphur dioxide pass through an alkali solution, for example, sodium hydroxide, then sodium sulfite is formed (or hydrosulfite - depending on how much alkali and sulfur dioxide are taken)

NaOH + SO 2 → NaHSO 3 - sulphur dioxide taken in excess

2NaOH + SO 2 → Na 2 SO 3 + H 2 O

If sulfur dioxide does not react with water, then why does its aqueous solution give an acidic reaction?! Yes, it does not react, but it oxidizes itself in water, adding oxygen to itself. And it turns out that free hydrogen atoms accumulate in the water, which give an acidic reaction (you can check it with some indicator!)