What is a base oxide. Chemistry - comprehensive preparation for external independent assessment

If you were not fond of chemistry at school, you are unlikely to immediately remember what oxides are and what their role is in environment. It is actually a fairly common type of compound that occurs most frequently in the environment in the form of water, rust, carbon dioxide, and sand. Oxides also include minerals - the species rocks having a crystalline structure.

Definition

Oxides are chemical compounds whose formula contains at least one oxygen atom and atoms of other chemical elements. Metal oxides generally contain oxygen anions in the -2 oxidation state. A significant part of the Earth's crust consists of solid oxides, which arose in the process of oxidizing elements with oxygen from air or water. The combustion of hydrocarbons produces two main oxides of carbon: carbon monoxide (carbon monoxide, CO) and carbon dioxide ( carbon dioxide, CO2).

Classification of oxides

All oxides are usually divided into two large groups:

• salt-forming oxides;
• non-salt-forming oxides.

Salt-forming oxides - chemical substances, in which, in addition to oxygen, elements of metals and non-metals are contained, which form acids upon contact with water, and when combined with bases - salts.

Salt-forming oxides, in turn, are divided into:

• basic oxides, in which, upon oxidation, the second element (1, 2 and sometimes 3-valent metal) becomes a cation (Li 2 O, Na 2 O, K 2 O, CuO, Ag 2 O, MgO, CaO, SrO, BaO, HgO , MnO, CrO, NiO, Fr 2 O, Cs 2 O, Rb 2 O, FeO);
• acid oxides, in which, during the formation of a salt, the second element is attached to a negatively charged oxygen atom (CO 2, SO 2, SO 3, SiO 2, P 2 O 5, CrO 3, Mn 2 O 7, NO 2, Cl 2 O 5, Cl2O3);
• amphoteric oxides, in which the second element (3 and 4-valent metals or such exceptions as zinc oxide, beryllium oxide, tin oxide and lead oxide) can become both a cation and join an anion (ZnO, Cr 2 O 3, Al 2 O 3 , SnO, SnO 2 , PbO, PbO 2 , TiO 2 , MnO 2 , Fe 2 O 3 , BeO).

Non-salt-forming oxides exhibit neither acidic nor basic nor amphoteric properties and, as the name suggests, do not form salts (CO, NO, NO 2 , (FeFe 2)O 4).

Properties of oxides

1. Oxygen atoms in oxides are highly reactive. Due to the fact that the oxygen atom is always negatively charged, it forms stable chemical bonds with almost all elements, which leads to a wide variety of oxides.
2. Noble metals such as gold and platinum are valued because they do not oxidize naturally. Corrosion of metals is formed as a result of hydrolysis or oxidation by oxygen. The combination of water and oxygen only speeds up the rate of the reaction.
3. In the presence of water and oxygen (or simply air), the oxidation reaction of some elements, such as sodium, occurs rapidly and can be dangerous to humans.
4. Oxides create a protective oxide film on the surface. An example is aluminum foil, which, due to the coating of a thin film of aluminum oxide, corrodes much more slowly.
5. The oxides of most metals have a polymeric structure, due to which they are not destroyed by the action of solvents.
6. Oxides dissolve under the action of acids and bases. Oxides that can react with both acids and bases are called amphoteric. Metals, as a rule, form basic oxides, non-metals - acidic oxides, and amphoteric oxides are obtained from alkali metals (metalloids).
7. The amount of metal oxide may be reduced by some organic compounds. Such redox reactions underlie many important chemical transformations, such as the detoxification of drugs by P450 enzymes and the production of ethylene oxide, which is then used to make antifreeze.

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Modern Encyclopedia

oxides- OXIDES, compounds of chemical elements (except fluorine) with oxygen. When interacting with water, they form bases (basic oxides) or acids (acidic oxides), many oxides are amphoteric. Most of the oxides normal conditions solids... ... Illustrated Encyclopedic Dictionary

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oxides- The combination of a chemical element with oxygen. By chemical properties, all oxides are divided into salt-forming (for example, Na2O, MgO, Al2O3, SiO2, P2O5, SO3, Cl2O7) and non-salt-forming (for example, CO, N2O, NO, H2O). Salt-forming oxides are divided into ... ... Technical Translator's Handbook

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Oxides are complex substances consisting of two elements, one of which is oxygen. Oxides can be salt-forming and non-salt-forming: one type of salt-forming oxides are basic oxides. How do they differ from other species, and what are their Chemical properties?

Salt-forming oxides are divided into basic, acidic and amphoteric oxides. If basic oxides correspond to bases, then acidic oxides correspond to acids, and amphoteric oxides correspond to amphoteric formations. Amphoteric oxides are compounds that, depending on the conditions, can exhibit either basic or acidic properties.

Rice. 1. Classification of oxides.

The physical properties of oxides are very diverse. They can be both gases (CO 2) and solid (Fe 2 O 3) or liquid substances (H 2 O).

However, most of the basic oxides are solids of various colors.

oxides in which the elements exhibit their highest activity are called higher oxides. The order of increase in the acidic properties of higher oxides of the corresponding elements in periods from left to right is explained by a gradual increase positive charge ions of these elements.

Chemical properties of basic oxides

Basic oxides are oxides that correspond to bases. For example, the basic oxides K 2 O, CaO correspond to the bases KOH, Ca (OH) 2.

Rice. 2. Basic oxides and their respective grounds.

Basic oxides are formed by typical metals, as well as metals of variable valence in the lowest oxidation state (for example, CaO, FeO), react with acids and acid oxides, forming salts:

CaO (basic oxide) + CO 2 (acid oxide) \u003d CaCO 3 (salt)

FeO (basic oxide) + H 2 SO 4 (acid) \u003d FeSO 4 (salt) + 2H 2 O (water)

Basic oxides also interact with amphoteric oxides, resulting in the formation of a salt, for example:

Only oxides of alkali and alkaline earth metals react with water:

BaO (basic oxide) + H 2 O (water) \u003d Ba (OH) 2 (alkaline earth metal base)

Many basic oxides tend to be reduced to substances consisting of atoms of one chemical element:

3CuO + 2NH 3 \u003d 3Cu + 3H 2 O + N 2

When heated, only oxides of mercury and precious metals decompose:

Rice. 3. Mercury oxide.

List of main oxides:

Chemical properties of basic oxides

Details about oxides, their classification and methods of obtaining can be read .

1. Interaction with water. Only basic oxides are capable of reacting with water, which correspond to soluble hydroxides (alkalis). Alkalis form alkali metals(lithium, sodium, potassium, rubidium and cesium) and alkaline earth (calcium, strontium, barium). Oxides of other metals do not chemically react with water. Magnesium oxide reacts with water when boiled.

CaO + H 2 O → Ca (OH) 2

CuO + H 2 O ≠

2. Interaction with acid oxides and acids. When basic oxides react with acids, a salt of this acid and water are formed. When a basic oxide and an acid react, a salt is formed:

basic oxide + acid = salt + water

basic oxide + acid oxide = salt

When basic oxides interact with acids and their oxides, the rule works:

At least one of the reagents must correspond to a strong hydroxide (alkali or strong acid).

In other words, basic oxides, which correspond to alkalis, react with all acidic oxides and their acids. Basic oxides, which correspond to insoluble hydroxides, react only with strong acids and their oxides (N 2 O 5 , NO 2 , SO 3 , etc.).

3. Interaction with amphoteric oxides and hydroxides.

When basic oxides interact with amphoteric ones, salts are formed:

basic oxide + amphoteric oxide = salt

During fusion, they interact with amphoteric oxides only basic oxides, which correspond to alkalis . This produces salt. The metal in the salt is taken from the more basic oxide, the acidic residue from the more acidic. In this case, the amphoteric oxide forms an acid residue.

K 2 O + Al 2 O 3 → 2KAlO 2

CuO + Al 2 O 3 ≠ (there is no reaction, because Cu (OH) 2 is an insoluble hydroxide)

(to determine the acid residue, add a water molecule to the formula of an amphoteric or acid oxide: Al 2 O 3 + H 2 O \u003d H 2 Al 2 O 4 and divide the resulting indices in half if the oxidation state of the element is odd: HAlO 2. It turns out an aluminate ion AlO 2 - The charge of the ion is easy to determine by the number of attached hydrogen atoms - if the hydrogen atom is 1, then the charge of the anion will be -1, if 2 hydrogen, then -2, etc.).

Amphoteric hydroxides decompose when heated, so they cannot actually react with basic oxides.

4. Interaction of basic oxides with reducing agents.

Thus, the ions of some metals are oxidizing agents (the more to the right in the series of voltages, the stronger). When interacting with reducing agents, metals go into oxidation state 0.

4.1. Recovery with coal or carbon monoxide.

Carbon (coal) restores from oxides only metals located in the activity series after aluminum. The reaction proceeds only when heated.

FeO + C → Fe + CO

Carbon monoxide also restores from oxides only metals located after aluminum in the electrochemical series:

Fe 2 O 3 + CO → Al 2 O 3 + CO 2

CuO + CO → Cu + CO 2

4.2. Hydrogen reduction .

Hydrogen reduces oxides only to metals located in the activity series to the right of aluminum. The reaction with hydrogen proceeds only under harsh conditions - under pressure and when heated.

CuO + H 2 → Cu + H 2 O

4.3. Recovery with more active metals (in melt or solution, depending on the metal)

In this case, more active metals displace less active ones. That is, the metal added to the oxide should be located to the left in the activity series than the metal from the oxide. Reactions usually proceed when heated.

For example , zinc oxide interacts with aluminum:

3ZnO + 2Al → Al 2 O 3 + 3Zn

but does not interact with copper:

ZnO + Cu ≠

Recovery of metals from oxides with the help of other metals is a very common process. Often, aluminum and magnesium are used to restore metals. But alkali metals are not very suitable for this - they are too chemically active, which creates difficulties when working with them.

For example, cesium explodes in air.

Aluminothermy is the reduction of metals from aluminum oxides.

For example : aluminum restores copper (II) oxide from oxide:

3CuO + 2Al → Al 2 O 3 + 3Cu

magnesiumthermy is the reduction of metals from magnesium oxides.

CuO + H 2 → Cu + H 2 O

4.4. Recovery with ammonia.

Ammonia can only reduce oxides of inactive metals. The reaction proceeds only at high temperature.

For example , ammonia reduces copper (II) oxide:

3CuO + 2NH 3 → 3Cu + 3H 2 O + N 2

5. Interaction of basic oxides with oxidizing agents.

Under the action of oxidizing agents, some basic oxides (in which metals can increase the degree of oxidation, for example, Fe 2+ , Cr 2+ , Mn 2+ , etc.) can act as reducing agents.

For example ,iron(II) oxide can be oxidized with oxygen to iron(III) oxide:

4FeO + O 2 → 2Fe 2 O 3

Oxides complex substances are called, the composition of the molecules of which includes oxygen atoms in the oxidation state - 2 and some other element.

can be obtained by direct interaction of oxygen with another element, or indirectly (for example, by the decomposition of salts, bases, acids). Under normal conditions, oxides are in a solid, liquid and gaseous state, this type of compounds is very common in nature. Oxides are found in the Earth's crust. Rust, sand, water, carbon dioxide are oxides.

They are salt-forming and non-salt-forming.

Salt-forming oxides are oxides that, as a result, chemical reactions form salts. These are oxides of metals and non-metals, which, when interacting with water, form the corresponding acids, and when interacting with bases, the corresponding acidic and normal salts. For example, copper oxide (CuO) is a salt-forming oxide, because, for example, when it reacts with hydrochloric acid (HCl), a salt is formed:

CuO + 2HCl → CuCl 2 + H 2 O.

As a result of chemical reactions, other salts can be obtained:

CuO + SO 3 → CuSO 4.

Non-salt-forming oxides called oxides that do not form salts. An example is CO, N 2 O, NO.

Salt-forming oxides, in turn, are of 3 types: basic (from the word « base » ), acidic and amphoteric.

Basic oxides such metal oxides are called, which correspond to hydroxides belonging to the class of bases. Basic oxides include, for example, Na 2 O, K 2 O, MgO, CaO, etc.

Chemical properties of basic oxides

1. Water-soluble basic oxides react with water to form bases:

Na 2 O + H 2 O → 2NaOH.

2. Interact with acid oxides, forming the corresponding salts

Na 2 O + SO 3 → Na 2 SO 4.

3. React with acids to form salt and water:

CuO + H 2 SO 4 → CuSO 4 + H 2 O.

4. React with amphoteric oxides:

Li 2 O + Al 2 O 3 → 2LiAlO 2 .

If the second element in the composition of the oxides is a non-metal or a metal exhibiting a higher valency (usually exhibits from IV to VII), then such oxides will be acidic. Acid oxides (acid anhydrides) are oxides that correspond to hydroxides belonging to the class of acids. This is, for example, CO 2, SO 3, P 2 O 5, N 2 O 3, Cl 2 O 5, Mn 2 O 7, etc. Acid oxides dissolve in water and alkalis, forming salt and water.

Chemical properties of acid oxides

1. Interact with water, forming acid:

SO 3 + H 2 O → H 2 SO 4.

But not all acidic oxides directly react with water (SiO 2 and others).

2. React with based oxides to form a salt:

CO 2 + CaO → CaCO 3

3. Interact with alkalis, forming salt and water:

CO 2 + Ba (OH) 2 → BaCO 3 + H 2 O.

Part amphoteric oxide includes an element that has amphoteric properties. Amphotericity is understood as the ability of compounds to exhibit acidic and basic properties depending on the conditions. For example, zinc oxide ZnO can be both a base and an acid (Zn(OH) 2 and H 2 ZnO 2). Amphotericity is expressed in the fact that, depending on the conditions, amphoteric oxides exhibit either basic or acidic properties.

Chemical properties of amphoteric oxides

1. Interact with acids to form salt and water:

ZnO + 2HCl → ZnCl 2 + H 2 O.

2. React with solid alkalis (during fusion), forming as a result of the reaction salt - sodium zincate and water:

ZnO + 2NaOH → Na 2 ZnO 2 + H 2 O.

When zinc oxide interacts with an alkali solution (the same NaOH), another reaction occurs:

ZnO + 2 NaOH + H 2 O => Na 2.

Coordination number - a characteristic that determines the number of nearest particles: atoms or ions in a molecule or crystal. Each amphoteric metal has its own coordination number. For Be and Zn it is 4; For and Al is 4 or 6; For and Cr it is 6 or (very rarely) 4;

Amphoteric oxides usually do not dissolve in water and do not react with it.

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