Oxides are complex substances consisting of two elements, one of which is oxygen in the second oxidation state.
In the chemical literature for the nomenclature of oxides adhere to the following rules:
- When writing formulas, oxygen is always put in second place - NO, CaO.
- When referring to oxides, the word oxide is always used first, followed by the second element in the genitive case: BaO - barium oxide, K₂O - potassium oxide.
- In the case when an element forms several oxides, the oxidation state of this element is indicated in parentheses after its name, for example N₂O₅ - nitric oxide (V), Fe₂O₃ - iron oxide (II), Fe₂O₃ - iron oxide (III).
- When naming the most common oxides, it is necessary to designate the atomic ratios in the molecule by the corresponding Greek numerals: N₂O - diazot oxide, NO - nitrogen dioxide, N₂O₅ - diazotone pentoxide, NO - nitrogen monoxide.
- Inorganic acid anhydrides are preferably called in the same way as oxides (for example, N₂O₅ - nitric oxide (V)).
Oxides can be obtained in several different ways:
- The interaction with oxygen of simple substances. Simple substances oxidize when heated, often with the release of heat and light. This process is called burning.
C + O₂ = CO₂ - Due to the oxidation of complex substances , oxides of elements are obtained, which are included in the composition of the starting substance:
2H₂S + 3O₂ = 2 H₂O + 2 SO₂ - The decomposition of nitrates, hydroxides, carbonates:
2Cu (NO₃) ₂ = 2CuO + 4NO₂ + O₂
CaCO₃ = CaO + CO₂
Cu (OH) ₂ = CuO + H₂O - As a result of the oxidation of metals by oxides of other elements. Similar reactions became the basis of metallothermy - the reduction of metals from their oxides with the help of more active metals:
2Al + Cr₂O₃ = 2Cr ± Al₂O₃ - By decomposition of higher oxides or by oxidation of lower:
4CrO₃ = 2Cr₂O₃ + 3O₃
4FeO + O₂ = 2Fe₂O₃
4CO + O₂ = 2CO₂
The classification of oxides based on their chemical properties implies their division into salt-forming and non-salt-forming oxides (indifferent). Salt-forming oxides, in turn, are divided into acidic, basic and amphoteric.
Base oxides correspond to basic oxides . For example, Na₂O, CaO, MgO are the main oxides, since they correspond to the bases - NaOH, Ca (OH) ₂, Mg (OH) ₂. Some oxides (K₂O and CaO) easily react with water and form the corresponding bases:
CaO + H₂O = Ca (OH) ₂
K₂O + H₂O = 2KOH
The oxides Fe₂O₃, CuO, Ag₂O do not react with water, but neutralize acids, due to which they are considered basic:
Fe₂O₃, + 6HCl = 2FeCl₃ + 3H₂OCuO + H₂SO₄ + H₂O
Ag₂O + 2HNO₃ = 2AgNO₃ + H₂O
Typical chemical properties of oxides of this type are their reaction with acids, as a result of which, as a rule, water and salt are formed:
FeO + 2HCl = FeCl₂ + H₂O
Basic oxides also react with acid oxides:
CaO + CO₂ = CaCO₃.
Acid oxides correspond to acids, for example, N₂O₃ oxide corresponds to nitric acid HNO₂, Cl₂O₇ - perchloric acid HClO₄, SO₃ - sulfuric acid H₂SO₄.
The main chemical property of such oxides is their reaction with bases, salt and water are formed:
2NaOH + CO₂ = NaCO₃ + H₂O
Most acid oxides react with water to form the corresponding acids. At the same time, SiO₂ oxide is practically insoluble in water, however, it neutralizes the bases, therefore, it is an acid oxide:
2NaOH + SiO₂ = (fusion) Na₂siO₃ + H₂O
Amphoteric oxides are oxides that, depending on conditions, exhibit acidic and basic properties, i.e. when interacting with acids, they behave as basic oxides, and when interacting with bases, they behave as acidic.
Not all amphoteric oxides interact with bases and acids to the same extent. Some have more pronounced basic properties, while others have acidic properties.
If zinc or chromium oxide equally reacts with acids and bases, then the basic properties of Fe O₃ oxide prevail.
The properties of amphoteric oxides are shown by the example of ZnO:
ZnO + 2HCl = ZnCl₂ + H₂O
ZnO + 2NaOH = Na₂ZnO₂ + H₂O
Non-salt forming oxides form neither acids nor bases (e.g. N₂O, NO).
In addition, they do not give reactions characteristic of salt-forming oxides. Non-salt-forming oxides can react with acids or alkalis, but no products characteristic of salt-forming oxides are formed, for example, at 150 ° C and 1.5 MPa, CO reacts with sodium hydroxide to form a sodium formate salt:
CO + NaOH = HCOONa
Non-salt-forming oxides are not as widespread as other types of oxides and are formed mainly with the participation of divalent non-metals.