General formula of chemistry bases. Chemical properties of bases

Bases are complex compounds that include two main structural components:

1. Hydroxo group (one or more). Hence, by the way, the second name for these substances is “hydroxides”.
2. Metal atom or ammonium ion (NH4+).

The name of the base comes from combining the names of both of its components: for example, calcium hydroxide, copper hydroxide, silver hydroxide, etc.

The only exception to the general rule of base formation should be considered when the hydroxo group is attached not to a metal, but to an ammonium cation (NH4+). This substance is formed when ammonia dissolves in water.

If we talk about the properties of bases, then it should immediately be noted that the valency of the hydroxo group is equal to one; accordingly, the number of these groups in the molecule will directly depend on the valence of the reacting metals. Examples in this case are the formulas of substances such as NaOH, Al(OH)3, Ca(OH)2.

The chemical properties of bases are manifested in their reactions with acids, salts, other bases, as well as in their action on indicators. In particular, alkalis can be determined by exposing their solution to a certain indicator. In this case, it will noticeably change its color: for example, it will turn from white to blue, and phenolphthalein will turn crimson.

The chemical properties of bases, manifested in their interaction with acids, lead to the famous neutralization reactions. The essence of this reaction is that metal atoms, joining the acidic residue, form a salt, and the hydroxo group and hydrogen ion, when combined, are converted into water. This reaction is called a neutralization reaction because after it there is no alkali or acid left.

The characteristic chemical properties of bases are also manifested in their reaction with salts. It is worth noting that only alkalis react with soluble salts. The structural features of these substances lead to the formation of a new salt and a new, most often insoluble, base as a result of the reaction.

Finally, the chemical properties of bases manifest themselves perfectly during thermal exposure to them - heating. Here, when carrying out certain experiments, it is worth keeping in mind that almost all bases, with the exception of alkalis, behave extremely unstable when heated. The vast majority of them decompose almost instantly into the corresponding oxide and water. And if we take the bases of metals such as silver and mercury, then under normal conditions they cannot be obtained, since they begin to decompose already at room temperature.

One of the classes of complex inorganic substances is bases. These are compounds that include metal atoms and a hydroxyl group, which can be split off when interacting with other substances.

Structure

Bases may contain one or more hydroxo groups. The general formula of the bases is Me(OH) x. There is always one metal atom, and the number of hydroxyl groups depends on the valence of the metal. In this case, the valency of the OH group is always I. For example, in the NaOH compound, the valency of sodium is I, therefore, there is one hydroxyl group. At the base Mg(OH) 2 the valence of magnesium is II, Al(OH) 3 the valence of aluminum is III.

The number of hydroxyl groups can vary in compounds with metals of variable valence. For example, Fe(OH) 2 and Fe(OH) 3. In such cases, the valence is indicated in parentheses after the name - iron (II) hydroxide, iron (III) hydroxide.

Physical properties

The characteristics and activity of the base depend on the metal. Most bases are odorless, white solids. However, some metals give the substance a characteristic color. For example, CuOH is yellow, Ni(OH) 2 is light green, Fe(OH) 3 is red-brown.

Rice. 1. Alkalis in solid state.

Kinds

The bases are classified according to two criteria:

• by number of OH groups- single-acid and multi-acid;
• by solubility in water- alkalis (soluble) and insoluble.

Alkalis are formed by alkali metals - lithium (Li), sodium (Na), potassium (K), rubidium (Rb) and cesium (Cs). In addition, active metals that form alkalis include the alkaline earth metals - calcium (Ca), strontium (Sr) and barium (Ba).

These elements form the following bases:

• LiOH;
• NaOH;
• RbOH;
• CsOH;
• Ca(OH) 2 ;
• Sr(OH)2;
• Ba(OH)2.

All other bases, for example, Mg(OH) 2, Cu(OH) 2, Al(OH) 3, are classified as insoluble.

In another way, alkalis are called strong bases, and insoluble alkalis are called weak bases. During electrolytic dissociation, alkalis quickly give up a hydroxyl group and react more quickly with other substances. Insoluble or weak bases are less active because do not donate a hydroxyl group.

Rice. 2. Classification of bases.

Amphoteric hydroxides occupy a special place in the systematization of inorganic substances. They interact with both acids and bases, i.e. Depending on the conditions, they behave like an alkali or an acid. These include Zn(OH) 2 , Al(OH) 3 , Pb(OH) 2 , Cr(OH) 3 , Be(OH) 2 and other bases.

Receipt

Bases are obtained in various ways. The simplest is the interaction of metal with water:

Ba + 2H 2 O → Ba(OH) 2 + H 2.

Alkalis are obtained by reacting the oxide with water:

Na 2 O + H 2 O → 2NaOH.

Insoluble bases are obtained as a result of the interaction of alkalis with salts:

CuSO 4 + 2NaOH → Cu(OH) 2 ↓+ Na 2 SO 4.

Chemical properties

The main chemical properties of the bases are described in the table.

Using the indicator, a test is carried out to determine the class of the base. When interacting with a base, litmus turns blue, phenolphthalein turns crimson, and methyl orange turns yellow.

Rice. 3. Reaction of indicators to bases.

What have we learned?

From the 8th grade chemistry lesson we learned about the features, classification and interaction of bases with other substances. Bases are complex substances consisting of a metal and a hydroxyl group OH. They are divided into soluble or alkali and insoluble. Alkalis are more aggressive bases that react quickly with other substances. Bases are obtained by reacting a metal or metal oxide with water, as well as by the reaction of a salt and an alkali. Bases react with acids, oxides, salts, metals and non-metals, and also decompose at high temperatures.

Test on the topic

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The general properties of bases are determined by the presence of the OH - ion in their solutions, which creates an alkaline environment in the solution (phenolphthalein turns crimson, methyl orange turns yellow, litmus turns blue).

1. Chemical properties of alkalis:

1) interaction with acid oxides:

2KOH+CO 2 ®K 2 CO 3 +H 2 O;

2) reaction with acids (neutralization reaction):

2NaOH+ H 2 SO 4 ®Na 2 SO 4 +2H 2 O;

3) interaction with soluble salts (only if, when an alkali acts on a soluble salt, a precipitate forms or a gas is released):

2NaOH+ CuSO 4 ®Cu(OH) 2 ¯+Na 2 SO 4,

Ba(OH) 2 +Na 2 SO 4 ®BaSO 4 ¯+2NaOH, KOH(conc.)+NH 4 Cl(crystalline) ®NH 3 +KCl+H 2 O.

2. Chemical properties of insoluble bases:

1) interaction of bases with acids:

Fe(OH) 2 +H 2 SO 4 ®FeSO 4 +2H 2 O;

2) decomposition when heated. When heated, insoluble bases decompose into the basic oxide and water:

Cu(OH) 2 ®CuO+H 2 O

End of work -

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Atomic molecular studies in chemistry. Atom. Molecule. Chemical element. Mol. Simple complex substances. Examples

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All topics in this section:

Getting grounds
1. Preparation of alkalis: 1) interaction of alkali or alkaline earth metals or their oxides with water: Ca+2H2O®Ca(OH)2+H

Nomenclature of acids
The names of acids are derived from the element from which the acid is formed. At the same time, the names of oxygen-free acids usually have the ending -hydrogen: HCl - hydrochloric, HBr - hydrobromo

Chemical properties of acids
The general properties of acids in aqueous solutions are determined by the presence of H+ ions formed during the dissociation of acid molecules, thus, acids are proton donors: HxAn«xH+

Obtaining acids
1) interaction of acid oxides with water: SO3+H2O®H2SO4, P2O5+3H2O®2H3PO4;

Chemical properties of acid salts
1) acid salts contain hydrogen atoms that can take part in the neutralization reaction, so they can react with alkalis, turning into medium or other acid salts - with a smaller number

Obtaining acid salts
The acid salt can be obtained: 1) by the reaction of incomplete neutralization of a polybasic acid with a base: 2H2SO4+Cu(OH)2®Cu(HSO4)2+2H

Basic salts.
Basic (hydroxo salts) are salts that are formed as a result of incomplete replacement of the hydroxide ions of the base with acid anions. Single acid bases, e.g. NaOH, KOH,

Chemical properties of basic salts
1) basic salts contain hydroxo groups that can take part in the neutralization reaction, so they can react with acids, turning into intermediate salts or basic salts with less

Preparation of basic salts
The main salt can be obtained: 1) by the reaction of incomplete neutralization of the base with an acid: 2Cu(OH)2+H2SO4®(CuOH)2SO4+2H2

Medium salts.
Medium salts are the products of complete replacement of H+ ions of an acid with metal ions; they can also be considered as products of complete replacement of the OH ions of the base anion

Nomenclature of medium salts
In Russian nomenclature (used in technological practice) there is the following order of naming medium salts: the word is added to the root of the name of an oxygen-containing acid

Chemical properties of medium salts
1) Almost all salts are ionic compounds, therefore, in a melt and in an aqueous solution, they dissociate into ions (when current is passed through solutions or molten salts, the process of electrolysis occurs).

Preparation of medium salts
Most of the methods for obtaining salts are based on the interaction of substances of opposite nature - metals with non-metals, acidic oxides with basic ones, bases with acids (see Table 2).

The structure of the atom.
An atom is an electrically neutral particle consisting of a positively charged nucleus and negatively charged electrons. The atomic number of an element in the Periodic Table of Elements is equal to the charge of the nucleus

Composition of atomic nuclei
The nucleus consists of protons and neutrons. The number of protons is equal to the atomic number of the element. The number of neutrons in the nucleus is equal to the difference between the mass number of the isotope and

Electron
Electrons rotate around the nucleus in certain stationary orbits. Moving along its orbit, an electron does not emit or absorb electromagnetic energy. Emission or absorption of energy occurs

Rule for filling electronic levels and sublevels of elements
The number of electrons that can be at one energy level is determined by the formula 2n2, where n is the number of the level. Maximum filling of the first four energy levels: for the first

Ionization energy, electron affinity, electronegativity.
Ionization energy of an atom. The energy required to remove an electron from an unexcited atom is called the first ionization energy (potential) I: E + I = E+ + e- Ionization energy

Covalent bond
In most cases, when a bond is formed, the electrons of the bonded atoms are shared. This type of chemical bond is called a covalent bond (the prefix "co-" in Latin

Sigma and pi connections.
Sigma (σ)-, pi (π)-bonds - an approximate description of the types of covalent bonds in molecules of various compounds, the σ-bond is characterized by the fact that the density of the electron cloud is maximum

Formation of a covalent bond by a donor-acceptor mechanism.
In addition to the homogeneous mechanism of covalent bond formation outlined in the previous section, there is a heterogeneous mechanism - the interaction of oppositely charged ions - the H+ proton and

Chemical bonding and molecular geometry. BI3, PI3
Figure 3.1 Addition of dipole elements in NH3 and NF3 molecules

Polar and non-polar bond
A covalent bond is formed as a result of the sharing of electrons (to form common electron pairs), which occurs during the overlap of electron clouds. In education

Ionic bond
An ionic bond is a chemical bond that occurs through the electrostatic interaction of oppositely charged ions. Thus, the process of education and

Oxidation state
Valency 1. Valency is the ability of atoms of chemical elements to form a certain number of chemical bonds. 2. Valency values ​​vary from I to VII (rarely VIII). Valens

Hydrogen bond
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Crystal lattices
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Solutions
If crystals of table salt, sugar or potassium permanganate (potassium permanganate) are placed in a vessel with water, then we can observe how the amount of solid substance gradually decreases. At the same time, water

Electrolytic dissociation
Solutions of all substances can be divided into two groups: electrolytes conduct electric current, non-electrolytes do not conduct electricity. This division is conditional, because everything

Dissociation mechanism.
Water molecules are dipole, i.e. one end of the molecule is negatively charged, the other is positively charged. The molecule has a negative pole approaching the sodium ion, and a positive pole approaching the chlorine ion; surround io

Ionic product of water
Hydrogen index (pH) is a value characterizing the activity or concentration of hydrogen ions in solutions. The hydrogen indicator is designated pH. The hydrogen index is numerically

Chemical reaction
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Methods for arranging coefficients in OVR
Electronic balance method 1). We write the equation of the chemical reaction KI + KMnO4 → I2 + K2MnO4 2). Finding atoms

Hydrolysis
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Rate of chemical reactions
The reaction rate is determined by a change in the molar concentration of one of the reactants: V = ± ((C2 – C1) / (t2 - t

Factors affecting the rate of chemical reactions
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Activation energy
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Catalysis catalyst
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Chemical equilibrium
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Le Chatelier's principle
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Factors influencing the rate of a chemical reaction
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Hess's law
Using table values

Thermal effect
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After reading the article, you will be able to separate substances into salts, acids and bases. The article describes what the pH of a solution is and what general properties acids and bases have.

Like metals and nonmetals, acids and bases are the division of substances based on similar properties. The first theory of acids and bases belonged to the Swedish scientist Arrhenius. According to Arrhenius, an acid is a class of substances that, when reacting with water, dissociate (decay), forming the hydrogen cation H +. Arrhenius bases in aqueous solution form OH - anions. The next theory was proposed in 1923 by scientists Bronsted and Lowry. The Brønsted-Lowry theory defines acids as substances capable of donating a proton in a reaction (a hydrogen cation is called a proton in reactions). Bases, accordingly, are substances that can accept a proton in a reaction. The currently relevant theory is the Lewis theory. Lewis theory defines acids as molecules or ions capable of accepting electron pairs, thereby forming Lewis adducts (an adduct is a compound formed by combining two reactants without forming by-products).

In inorganic chemistry, as a rule, an acid means a Bronsted-Lowry acid, that is, substances capable of donating a proton. If they mean the definition of a Lewis acid, then in the text such an acid is called a Lewis acid. These rules apply to acids and bases.

Dissociation

Dissociation is the process of decomposition of a substance into ions in solutions or melts. For example, the dissociation of hydrochloric acid is the decomposition of HCl into H + and Cl -.

Properties of acids and bases

Bases tend to feel soapy to the touch, while acids generally taste sour.

When a base reacts with many cations, a precipitate is formed. When an acid reacts with anions, a gas is usually released.

Commonly used acids:
H 2 O, H 3 O +, CH 3 CO 2 H, H 2 SO 4, HSO 4 −, HCl, CH 3 OH, NH 3

Commonly used bases:
OH − , H 2 O , CH 3 CO 2 − , HSO 4 − , SO 4 2 − , Cl −

Strong and weak acids and bases

Strong acids

Such acids that completely dissociate in water, producing hydrogen cations H + and anions. An example of a strong acid is hydrochloric acid HCl:

HCl (solution) + H 2 O (l) → H 3 O + (solution) + Cl - (solution)

Examples of strong acids: HCl, HBr, HF, HNO 3, H 2 SO 4, HClO 4

List of strong acids

• HCl - hydrochloric acid
• HBr - hydrogen bromide
• HI - hydrogen iodide
• HNO 3 - nitric acid
• HClO 4 - perchloric acid
• H 2 SO 4 - sulfuric acid

Weak acids

Only partially dissolved in water, for example, HF:

HF (solution) + H2O (l) → H3O + (solution) + F - (solution) - in such a reaction more than 90% of the acid does not dissociate:
= < 0,01M для вещества 0,1М

Strong and weak acids can be distinguished by measuring the conductivity of solutions: conductivity depends on the number of ions, the stronger the acid, the more dissociated it is, therefore, the stronger the acid, the higher the conductivity.

List of weak acids

• HF hydrogen fluoride
• H 3 PO 4 phosphoric
• H 2 SO 3 sulfurous
• H 2 S hydrogen sulfide
• H 2 CO 3 coal
• H 2 SiO 3 silicon

Strong grounds

Strong bases completely dissociate in water:

NaOH (solution) + H 2 O ↔ NH 4

Strong bases include metal hydroxides of the first (alkalines, alkali metals) and second (alkalinotherrenes, alkaline earth metals) groups.

List of strong bases

• NaOH sodium hydroxide (caustic soda)
• KOH potassium hydroxide (caustic potash)
• LiOH lithium hydroxide
• Ba(OH) 2 barium hydroxide
• Ca(OH) 2 calcium hydroxide (slaked lime)

Weak foundations

In a reversible reaction in the presence of water, it forms OH - ions:

NH 3 (solution) + H 2 O ↔ NH + 4 (solution) + OH - (solution)

Most weak bases are anions:

F - (solution) + H 2 O ↔ HF (solution) + OH - (solution)

List of weak bases

• Mg(OH) 2 magnesium hydroxide
• Fe(OH) 2 iron(II) hydroxide
• Zn(OH) 2 zinc hydroxide
• NH 4 OH ammonium hydroxide
• Fe(OH) 3 iron(III) hydroxide

Reactions of acids and bases

Strong acid and strong base

This reaction is called neutralization: when the amount of reagents is sufficient to completely dissociate the acid and base, the resulting solution will be neutral.

Example:
H 3 O + + OH - ↔ 2H 2 O

Weak base and weak acid

General type of reaction:
Weak base (solution) + H 2 O ↔ Weak acid (solution) + OH - (solution)

Strong base and weak acid

The base dissociates completely, the acid dissociates partially, the resulting solution has weak properties of a base:

HX (solution) + OH - (solution) ↔ H 2 O + X - (solution)

Strong acid and weak base

The acid dissociates completely, the base does not dissociate completely:

Dissociation of water

Dissociation is the breakdown of a substance into its component molecules. The properties of an acid or base depend on the equilibrium that is present in water:

H 2 O + H 2 O ↔ H 3 O + (solution) + OH - (solution)
K c = / 2
The equilibrium constant of water at t=25°: K c = 1.83⋅10 -6, the following equality also holds: = 10 -14, which is called the dissociation constant of water. For pure water = = 10 -7, hence -lg = 7.0.

This value (-lg) is called pH - hydrogen potential. If pH< 7, то вещество имеет кислотные свойства, если pH >7, then the substance has basic properties.

Methods for determining pH

Instrumental method

A special device, a pH meter, is a device that transforms the concentration of protons in a solution into an electrical signal.

Indicators

A substance that changes color in a certain pH range depending on the acidity of the solution; using several indicators you can achieve a fairly accurate result.

Salt

A salt is an ionic compound formed by a cation other than H+ and an anion other than O2-. In a weak aqueous solution, the salts completely dissociate.

To determine the acid-base properties of a salt solution, it is necessary to determine which ions are present in the solution and consider their properties: neutral ions formed from strong acids and bases do not affect pH: they do not release either H + or OH - ions in water. For example, Cl -, NO - 3, SO 2- 4, Li +, Na +, K +.

Anions formed from weak acids exhibit alkaline properties (F -, CH 3 COO -, CO 2- 3); cations with alkaline properties do not exist.

All cations except metals of the first and second groups have acidic properties.

Buffer solution

Solutions that maintain their pH level when a small amount of a strong acid or a strong base is added are mainly composed of:

• A mixture of a weak acid, its corresponding salt and a weak base
• Weak base, corresponding salt and strong acid

To prepare a buffer solution of a certain acidity, it is necessary to mix a weak acid or base with the appropriate salt, taking into account:

• pH range in which the buffer solution will be effective
• Solution capacity - the amount of strong acid or strong base that can be added without affecting the pH of the solution
• There should be no unwanted reactions that could change the composition of the solution

Test:

Metal and hydroxyl group (OH). For example, sodium hydroxide - NaOH, calcium hydroxide - Ca(OH) 2 , barium hydroxide - Ba(OH) 2, etc.

Preparation of hydroxides.

1. Exchange reaction:

CaSO 4 + 2NaOH = Ca(OH) 2 + Na 2 SO 4,

2. Electrolysis of aqueous salt solutions:

2KCl + 2H 2 O = 2KOH + H 2 + Cl 2,

3. Interaction of alkali and alkaline earth metals or their oxides with water:

K+2H 2 O = 2 KOH + H 2 ,

Chemical properties of hydroxides.

1. Hydroxides are alkaline in nature.

2. Hydroxides dissolves in water (alkali) and is insoluble. For example, KOH- dissolves in water, and Ca(OH) 2 - slightly soluble, white solution. Metals of group 1 of the periodic table D.I. Mendeleev gives soluble bases (hydroxides).

3. Hydroxides decompose when heated:

Cu(OH) 2 = CuO + H 2 O.

4. Alkalis react with acidic and amphoteric oxides:

2KOH + CO 2 = K 2 CO 3 + H 2 O.

5. Alkalis can react with some non-metals in different ways at different temperatures:

NaOH + Cl 2 = NaCl + NaOCl + H 2 O(cold),

NaOH + 3 Cl 2 = 5 NaCl + NaClO 3 + 3 H 2 O(heat).

6. Interact with acids:

KOH + HNO3 = KNO 3 + H 2 O.