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18. OXIDES. CLASSIFICATION. RECEIVING. PROPERTIES.
Oxides are the complex substances consisting of two chemical elements, one of which oxygen, with oxidation level-2. Only one chemical element - fluorine, connecting to oxygen, forms not oxide, but OF2 oxygen fluoride.
They are called simply - "oxide + the name of element" (see below). If the valency of chemical element variable, then is specified in the Roman figure concluded in parentheses after the name of chemical element.
| Formula | Name | Formula | Name |
| CO | carbon oxide (II) | Fe2O3 | iron oxide (III) |
| NO | nitrogen oxide (II) | CrO3 | chromium oxide (VI) |
| N2O5 | nitrogen oxide (V) | Mn2O7 | manganese oxide (VII) |
Classification of oxides.
To the main oxides there correspond the bases, acid - acids. Metal oxides of the main subgroups of the I-II groups, and also metals of secondary subgroups with oxidation level +1 and +2 concern to the main (except zinc and berriliya). Carry oxides of nonmetals to acid, except not salt-forming, and also metal oxides of secondary subgroups with oxidation level from +5 to +7 (CrO3-chromium oxide (VI), Mn 2O7 - manganese oxide (VII)). The main react with acids, acid with the bases. The third group of oxides, reacts both with acids, and with the bases, they are called amphoteric. Metal oxides of the main and secondary subgroups with the oxidation level +3, sometimes +4, and also zinc and beryllium concern to them. I.e. the nature of properties of oxides first of all depends on oxidation level. For example CrO chromium oxides (+2 - osnovny)-> Cr 2O3(+3 - amphoteric)-> CrO3 (+6 - acid).
In periodic system in groups the main properties are weakened from left to right, amplify - acid. From top to down in groups the main amplify, acid are weakened.Receiving oxides.
| Oxidation by oxygen | simple substances |
2Mg +O2=2MgO
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| complex substances |
2H2S+3O2=2H2O+2SO2
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| Decomposition | heating of salts |
SACO3=CAO+CO2
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| heating of the bases |
Cu (OH)2=CuO+H20
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| heating of oxygen-containing acids |
H2SO3=H2O+SO2
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| heating of the highest oxides |
4CrO3=Cr2O3+3O2
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| Oxidation of the lowest oxides | 4FeO+O2=2Fe2O3 | |
| Replacement of volatile oxide by less flying | Na2CO3+SiO2=Na2SiO3+CO2 |
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Chemical properties of oxides.
The main Amphoteric Acid The main - react a lot of acid with formation of salt and water. To the main oxides there correspond the bases.
1. Interaction with water (oxides of alkaline and alkaline-earth mt.)
CaO+H2O=Ca(OH)2
2. All - with acids
AI2O3+6HCl=2AlCl3+3H2O
3. From kislotnyama oxides
CaO+CO2=CaCO3
4. With amphoteric oxides
Li2O+Al2O3=2LiAlO2Amphoteric (ZnO, Al2O3, Cr2O3, MnO2)
1. Interact both with acids, and with the bases.
ZnO+2HCl=ZnCl2+H2O
ZnO+2NaOH+H2O=Na2 [Zn(OH)4]
2. React with the main and acid oxides
ZnO+CaO=CaZnO2
ZnO+SiO2=ZnSiO3
Acid - react a lot of alkali with formation of salt and water. To acid oxides often there correspond acids.
1. The majority interact with water
SO3+H2O=H2SO4
2. With alkalis
NaOH+SiO2=Na2SiO3+H2O
3. With the main oxides
SiO2+CaO=CaSiO3
4. With amphoteric oxides
Al2O3+3SO3=Al2(SO4)3