What does the base react with? Chemical properties of bases

Insoluble base: copper hydroxide

Foundations- called electrolytes, in the solutions of which there are no anions, except for hydroxide ions (anions are ions that have a negative charge, in this case they are OH - ions). Titles grounds consists of three parts: words hydroxide , to which the name of the metal is added (in the genitive case). For example, copper hydroxide(Cu(OH) 2). For some grounds old names may be used, for example sodium hydroxide(NaOH) - sodium alkali.

Sodium hydroxide, sodium hydroxide, sodium alkali, caustic soda- all this is the same substance, the chemical formula of which is NaOH. Anhydrous sodium hydroxide is a white crystalline substance. A solution is a clear liquid that looks indistinguishable from water. Be careful when using! Caustic soda burns the skin severely!

The classification of bases is based on their ability to dissolve in water. Some properties of bases depend on solubility in water. So, grounds that are soluble in water are called alkali. These include sodium hydroxides(NaOH), potassium hydroxide(KOH), lithium (LiOH), sometimes they are added to their number and calcium hydroxide(Ca (OH) 2)), although in fact it is a slightly soluble white substance (slaked lime).

Getting the grounds

Getting the grounds And alkalis can be done in various ways. For getting alkalis You can use the chemical interaction of metal with water. Such reactions proceed with a very large release of heat, up to ignition (ignition occurs due to the release of hydrogen during the reaction).

2Na + 2H 2 O → 2NaOH + H 2

Quicklime - CaO

CaO + H 2 O → Ca (OH) 2

But in industry, these methods have not found practical value, of course, except for the production of calcium hydroxide Ca (OH) 2. Receipt sodium hydroxide And potassium hydroxide associated with the use of electricity. During the electrolysis of an aqueous solution of sodium or potassium chloride, hydrogen is released at the cathode, and chlorine at the anode, while in the solution where electrolysis occurs, accumulates alkali!

KCl + 2H 2 O → 2KOH + H 2 + Cl 2 (this reaction takes place when an electric current is passed through the solution).

Insoluble bases besiege alkalis from solutions of the corresponding salts.

CuSO 4 + 2NaOH → Cu(OH) 2 + Na 2 SO 4

Base properties

alkalis heat resistant. Sodium hydroxide you can melt and bring the melt to a boil, while it will not decompose. alkalis easily react with acids, resulting in the formation of salt and water. This reaction is also called the neutralization reaction.

KOH + HCl → KCl + H2O

alkalis interact with acidic oxides, as a result of which salt and water are formed.

2NaOH + CO 2 → Na 2 CO 3 + H 2 O

Insoluble bases, unlike alkalis, are not thermally stable substances. Some of them, for example, copper hydroxide, decompose when heated,

Cu(OH) 2 + CuO → H 2 O
others - even at room temperature (for example, silver hydroxide - AgOH).

Insoluble bases interact with acids, the reaction occurs only if the salt that is formed during the reaction dissolves in water.

Cu(OH) 2 + 2HCl → CuCl 2 + 2H 2 O

Dissolution of an alkali metal in water with a change in the color of the indicator to bright red

Alkali metals are metals that react with water to form alkali. Sodium Na is a typical representative of alkali metals. Sodium is lighter than water, so its chemical reaction with water occurs on its surface. Actively dissolving in water, sodium displaces hydrogen from it, while forming sodium alkali (or sodium hydroxide) - caustic soda NaOH. The reaction proceeds as follows:

2Na + 2H 2 O → 2NaOH + H 2

All alkali metals behave in a similar way. If, before starting the reaction, the indicator phenolphthalein is added to the water, and then a piece of sodium is dipped into the water, then the sodium will slide through the water, leaving behind a bright pink trace of the formed alkali (alkali turns phenolphthalein pink)

iron hydroxide

iron hydroxide is the basis. Iron, depending on the degree of its oxidation, forms two different bases: iron hydroxide, where iron can have valencies (II) - Fe (OH) 2 and (III) - Fe (OH) 3. Like the bases formed by most metals, both iron bases are insoluble in water.

iron hydroxide(II) - white gelatinous substance (precipitate in solution), which has strong reducing properties. Besides, iron hydroxide(II) very unstable. If to a solution iron hydroxide(II) add a little alkali, then a green precipitate will fall out, which darkens rather quickly and turns into a brown precipitate of iron (III).

iron hydroxide(III) has amphoteric properties, but its acidic properties are much less pronounced. Get iron hydroxide(III) is possible as a result of a chemical exchange reaction between an iron salt and an alkali. For example

Fe 2 (SO 4) 3 + 6 NaOH → 3 Na 2 SO 4 +2 Fe (OH) 3

Alkali metal hydroxides - under normal conditions, they are solid white crystalline substances, hygroscopic, soapy to the touch, very soluble in water (their dissolution is an exothermic process), fusible. Hydroxides of alkaline earth metals Ca (OH) 2, Sr (OH) 2, Ba (OH) 2) are white powdery substances, much less soluble in water compared to alkali metal hydroxides. Water-insoluble bases usually form as gel-like precipitates that decompose on storage. For example, Cu (OH) 2 is a blue gelatinous precipitate.

3.1.4 Chemical properties of bases.

The properties of bases are due to the presence of OH - ions. There are differences in the properties of alkalis and water-insoluble bases, but the common property is the reaction of interaction with acids. The chemical properties of the bases are presented in table 6.

Table 6 - Chemical properties of bases

alkalis	Insoluble bases
All bases react with acids ( neutralization reaction)
2NaOH + H 2 SO 4 \u003d Na 2 SO 4 + 2H 2 O	Cr(OH) 2 + 2HC1 = CrC1 2 + 2H 2 O
Bases react with acidic oxides with the formation of salt and water: 6KOH + P 2 O 5 \u003d 2K 3 RO 4 + 3H 2 O
Alkalis react with salt solutions if one of the reaction products precipitates out(i.e. if an insoluble compound forms): CuSO 4 + 2KOH \u003d Cu (OH) 2  + K 2 SO 4 Na 2 SO 4 + Ba(OH) 2 = 2NaOH + BaSO 4 	Water-insoluble bases and amphoteric hydroxides decompose when heated to the corresponding oxide and water: Mn (OH) 2  MnO + H 2 O Cu (OH) 2  CuO + H 2 O
Alkalis can be detected with an indicator. In an alkaline environment: litmus - blue, phenolphthalein - raspberry, methyl orange - yellow

3.1.5 Essential foundations.

NaOH- caustic soda, caustic soda. Fusible (t pl = 320 °C) white hygroscopic crystals, highly soluble in water. The solution is soapy to the touch and is a dangerous caustic liquid. NaOH is one of the most important products of the chemical industry. It is required in large quantities for the purification of petroleum products, and is widely used in soap, paper, textile and other industries, as well as for the production of artificial fiber.

KOH- caustic potash. White hygroscopic crystals, highly soluble in water. The solution is soapy to the touch and is a dangerous caustic liquid. The properties of KOH are similar to those of NaOH, but potassium hydroxide is used much less frequently due to its higher cost.

Ca(OH) 2 - slaked lime. White crystals, slightly soluble in water. The solution is called “lime water”, the suspension is called “milk of lime”. Lime water is used to recognize carbon dioxide, it becomes cloudy when CO 2 is passed through. Hydrated lime is widely used in the construction industry as a basis for the manufacture of binders.

Modern chemical science is a wide variety of branches, and each of them, in addition to the theoretical base, is of great applied and practical importance. Whatever you touch, everything around is the products of chemical production. The main sections are inorganic and organic chemistry. Consider what main classes of substances are classified as inorganic and what properties they have.

Main categories of inorganic compounds

These include the following:

Oxides.
Salt.
Foundations.
Acids.

Each of the classes is represented by a wide variety of inorganic compounds and is important in almost any structure of human economic and industrial activity. All the main properties characteristic of these compounds, being in nature and obtaining are studied in the school chemistry course without fail, in grades 8-11.

There is a general table of oxides, salts, bases, acids, which presents examples of each of the substances and their state of aggregation, being in nature. It also shows interactions that describe chemical properties. However, we will consider each of the classes separately and in more detail.

Group of compounds - oxides

4. Reactions, as a result of which elements change CO

Me + n O + C = Me 0 + CO

1. Reagent water: acid formation (SiO 2 exception)

KO + water = acid

2. Reactions with bases:

CO 2 + 2CsOH \u003d Cs 2 CO 3 + H 2 O

3. Reactions with basic oxides: salt formation

P 2 O 5 + 3MnO \u003d Mn 3 (PO 3) 2

4. OVR reactions:

CO 2 + 2Ca \u003d C + 2CaO,

They show dual properties, interact according to the principle of the acid-base method (with acids, alkalis, basic oxides, acid oxides). They do not interact with water.

1. With acids: formation of salts and water

AO + acid \u003d salt + H 2 O

2. With bases (alkalis): formation of hydroxo complexes

Al 2 O 3 + LiOH + water \u003d Li

3. Reactions with acid oxides: preparation of salts

FeO + SO 2 \u003d FeSO 3

4. Reactions with RO: formation of salts, fusion

MnO + Rb 2 O = double salt Rb 2 MnO 2

5. Fusion reactions with alkalis and alkali metal carbonates: formation of salts

Al 2 O 3 + 2LiOH \u003d 2LiAlO 2 + H 2 O

They do not form acids or alkalis. They exhibit highly specific properties.

Each higher oxide, formed both by a metal and a non-metal, when dissolved in water, gives a strong acid or alkali.

Acids organic and inorganic

In the classical sound (based on the positions of ED - electrolytic dissociation - Svante Arrhenius), acids are compounds that dissociate into H + cations and anions of An acid residues in an aqueous medium. Today, however, acids have been carefully studied under anhydrous conditions, so there are many different theories for hydroxides.

Empirical formulas of oxides, bases, acids, salts are made up only of symbols, elements and indices indicating their amount in a substance. For example, inorganic acids are expressed by the formula H + acid residue n-. Organic substances have a different theoretical mapping. In addition to the empirical one, it is possible to write down a full and abbreviated structural formula for them, which will reflect not only the composition and amount of the molecule, but also the arrangement of atoms, their relationship to each other and the main functional group for carboxylic acids -COOH.

In the inorganic, all acids are divided into two groups:

anoxic - HBr, HCN, HCL and others;
oxygen-containing (oxo acids) - HClO 3 and everything where there is oxygen.

Also, inorganic acids are classified by stability (stable or stable - everything except carbonic and sulphurous, unstable or unstable - carbonic and sulphurous). By strength, acids can be strong: sulfuric, hydrochloric, nitric, perchloric and others, as well as weak: hydrogen sulfide, hypochlorous and others.

Organic chemistry does not offer such diversity at all. Acids that are organic in nature are carboxylic acids. Their common feature is the presence of a functional group -COOH. For example, HCOOH (antic), CH 3 COOH (acetic), C 17 H 35 COOH (stearic) and others.

There are a number of acids, which are especially carefully emphasized when considering this topic in a school chemistry course.

Salt.
Nitrogen.
Orthophosphoric.
Hydrobromic.
Coal.
Iodine.
Sulfuric.
Acetic, or ethane.
Butane or oil.
Benzoic.

These 10 acids in chemistry are the fundamental substances of the corresponding class both in the school course and in general in industry and synthesis.

Properties of inorganic acids

The main physical properties should be attributed primarily to a different state of aggregation. After all, there are a number of acids that have the form of crystals or powders (boric, orthophosphoric) under normal conditions. The vast majority of known inorganic acids are different liquids. Boiling and melting points also vary.

Acids can cause severe burns, as they have the power to destroy organic tissues and skin. Indicators are used to detect acids:

methyl orange (in normal environment - orange, in acids - red),
litmus (in neutral - violet, in acids - red) or some others.

The most important chemical properties include the ability to interact with both simple and complex substances.

Chemical properties of inorganic acids

What do they interact with?	Reaction example
1. With simple substances-metals. Mandatory condition: the metal must stand in the ECHRNM before hydrogen, since the metals standing after hydrogen are not able to displace it from the composition of acids. As a result of the reaction, hydrogen is always formed in the form of a gas and a salt.
2. With bases. The result of the reaction is salt and water. Such reactions of strong acids with alkalis are called neutralization reactions.	Any acid (strong) + soluble base = salt and water
3. With amphoteric hydroxides. Bottom line: salt and water.	2HNO 2 + beryllium hydroxide \u003d Be (NO 2) 2 (medium salt) + 2H 2 O
4. With basic oxides. Outcome: water, salt.	2HCL + FeO = iron (II) chloride + H 2 O
5. With amphoteric oxides. Final effect: salt and water.	2HI + ZnO = ZnI 2 + H 2 O
6. With salts formed by weaker acids. Final effect: salt and weak acid.	2HBr + MgCO 3 = magnesium bromide + H 2 O + CO 2

When interacting with metals, not all acids react in the same way. Chemistry (grade 9) at school involves a very shallow study of such reactions, however, even at this level, the specific properties of concentrated nitric and sulfuric acid when interacting with metals are considered.

Hydroxides: alkalis, amphoteric and insoluble bases

Oxides, salts, bases, acids - all these classes of substances have a common chemical nature, which is explained by the structure of the crystal lattice, as well as the mutual influence of atoms in the composition of molecules. However, if for oxides it was possible to give a very specific definition, then for acids and bases it is more difficult to do so.

Just like acids, according to the ED theory, bases are substances that can decompose in an aqueous solution into metal cations Me n + and anions of hydroxo groups OH -.

Soluble or alkali (strong bases that change the color of the indicators). Formed by metals I, II groups. Example: KOH, NaOH, LiOH (that is, elements of only the main subgroups are taken into account);
Slightly soluble or insoluble (medium strength, do not change the color of the indicators). Example: magnesium hydroxide, iron (II), (III) and others.
Molecular (weak bases, in an aqueous medium they reversibly dissociate into ions-molecules). Example: N 2 H 4, amines, ammonia.
Amphoteric hydroxides (show dual basic-acid properties). Example: beryllium, zinc and so on.

Each group represented is studied in the school chemistry course in the "Foundations" section. Chemistry grades 8-9 involves a detailed study of alkalis and sparingly soluble compounds.

The main characteristic properties of the bases

All alkalis and sparingly soluble compounds are found in nature in a solid crystalline state. At the same time, their melting points are, as a rule, low, and poorly soluble hydroxides decompose when heated. The base color is different. If the alkalis are white, then the crystals of sparingly soluble and molecular bases can be of very different colors. The solubility of most compounds of this class can be viewed in the table, which presents the formulas of oxides, bases, acids, salts, shows their solubility.

Alkalis are able to change the color of indicators as follows: phenolphthalein - raspberry, methyl orange - yellow. This is ensured by the free presence of hydroxo groups in solution. That is why sparingly soluble bases do not give such a reaction.

The chemical properties of each group of bases are different.

Chemical properties

alkalis

sparingly soluble bases

Amphoteric hydroxides

I. Interact with KO (total - salt and water):

2LiOH + SO 3 = Li 2 SO 4 + water

II. Interact with acids (salt and water):

conventional neutralization reactions (see acids)

III. Interact with AO to form a hydroxocomplex of salt and water:

2NaOH + Me + n O \u003d Na 2 Me + n O 2 + H 2 O, or Na 2

IV. Interact with amphoteric hydroxides to form hydroxo complex salts:

The same as with AO, only without water

V. Interact with soluble salts to form insoluble hydroxides and salts:

3CsOH + iron (III) chloride = Fe(OH) 3 + 3CsCl

VI. Interact with zinc and aluminum in an aqueous solution to form salts and hydrogen:

2RbOH + 2Al + water = complex with hydroxide ion 2Rb + 3H 2

I. When heated, they can decompose:

insoluble hydroxide = oxide + water

II. Reactions with acids (total: salt and water):

Fe(OH) 2 + 2HBr = FeBr 2 + water

III. Interact with KO:

Me + n (OH) n + KO \u003d salt + H 2 O

I. React with acids to form salt and water:

(II) + 2HBr = CuBr 2 + water

II. React with alkalis: result - salt and water (condition: fusion)

Zn(OH) 2 + 2CsOH \u003d salt + 2H 2 O

III. They react with strong hydroxides: the result is salts, if the reaction takes place in an aqueous solution:

Cr(OH) 3 + 3RbOH = Rb 3

These are the most chemical properties that bases exhibit. The chemistry of bases is quite simple and obeys the general laws of all inorganic compounds.

Class of inorganic salts. Classification, physical properties

Based on the provisions of the ED, salts can be called inorganic compounds that dissociate in an aqueous solution into metal cations Me + n and anions of acid residues An n-. So you can imagine salt. Chemistry gives more than one definition, but this is the most accurate.

At the same time, according to their chemical nature, all salts are divided into:

Acidic (containing a hydrogen cation). Example: NaHSO4.
Basic (having a hydroxo group). Example: MgOHNO 3 , FeOHCL 2.
Medium (consist only of a metal cation and an acid residue). Example: NaCL, CaSO 4.
Double (include two different metal cations). Example: NaAl(SO 4) 3.
Complex (hydroxocomplexes, aquacomplexes and others). Example: K 2 .

The formulas of salts reflect their chemical nature, and also speak of the qualitative and quantitative composition of the molecule.

Oxides, salts, bases, acids have different solubility, which can be seen in the corresponding table.

If we talk about the state of aggregation of salts, then you need to notice their uniformity. They exist only in a solid, crystalline or powdered state. The color scheme is quite varied. Solutions of complex salts, as a rule, have bright saturated colors.

Chemical interactions for the class of medium salts

They have similar chemical properties of bases, acids, salts. Oxides, as we have already considered, differ somewhat from them in this factor.

In total, 4 main types of interactions can be distinguished for medium salts.

I. Interaction with acids (only strong in terms of ED) with the formation of another salt and a weak acid:

KCNS + HCL = KCL + HCNS

II. Reactions with soluble hydroxides with the appearance of salts and insoluble bases:

CuSO 4 + 2LiOH = 2LiSO 4 soluble salt + Cu(OH) 2 insoluble base

III. Interaction with another soluble salt to form an insoluble salt and a soluble one:

PbCL 2 + Na 2 S = PbS + 2NaCL

IV. Reactions with metals to the left of the one that forms the salt in the EHRNM. In this case, the metal entering into the reaction should not, under normal conditions, interact with water:

Mg + 2AgCL = MgCL 2 + 2Ag

These are the main types of interactions that are characteristic of medium salts. The formulas of complex, basic, double and acidic salts speak for themselves about the specificity of the manifested chemical properties.

The formulas of oxides, bases, acids, salts reflect the chemical essence of all representatives of these classes of inorganic compounds, and in addition, they give an idea of the name of the substance and its physical properties. Therefore, special attention should be paid to their writing. A huge variety of compounds offers us a generally amazing science - chemistry. Oxides, bases, acids, salts - this is only part of the vast variety.

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

Obtaining hydroxides.

1. Exchange reaction:

CaSO 4 + 2NaOH \u003d Ca (OH) 2 + Na 2 SO 4,

2. Electrolysis of aqueous solutions of salts:

2KCl + 2H 2 O \u003d 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 dissolve in water (alkali) and are insoluble. For example, KOH- dissolves in water Ca(Oh) 2 - slightly soluble, has a white solution. Metals of the 1st group of the periodic table D.I. Mendeleev give 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 \u003d K 2 CO 3 + H 2 O.

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

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.

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, what common properties acids and bases have.

Like metals and non-metals, acids and bases are the separation of substances according to similar properties. The first theory of acids and bases belonged to the Swedish scientist Arrhenius. An Arrhenius acid is a class of substances that, in reaction with water, dissociate (decompose), forming a hydrogen cation H +. Arrhenius bases in aqueous solution form OH - anions. The following theory was proposed in 1923 by the scientists Brönsted 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, respectively, are substances capable of accepting a proton in a reaction. The current 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, by acid they mean 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 are valid for acids and bases.

Dissociation

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

Properties of acids and bases

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

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

Dissolve in water only partially, 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: the 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 hydrofluoric
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 bases

Strong bases completely dissociate in water:

NaOH (solution) + H 2 O ↔ NH 4

Strong bases include hydroxides of metals of the first (alkalins, alkali metals) and the second (alcaline terrenes, 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 bases

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

Such a reaction is called neutralization: if 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 view of the reaction:
Weak base (solution) + H 2 O ↔ Weak acid (solution) + OH - (solution)

Strong base and weak acid

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

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

Strong acid and weak base

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

Water dissociation

Dissociation is the breakdown of a substance into its constituent 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 takes place: = 10 -14 , which is called the dissociation constant of water. For pure water = = 10 -7 , whence -lg = 7.0.

This value (-lg) is called pH - the potential of hydrogen. 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 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 range of pH values 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 O 2- . In a weak aqueous solution, 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: neither H + nor OH - ions are released 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 for metals of the first and second groups, have acidic properties.

buffer solution

Solutions that maintain their pH when a small amount of a strong acid or strong base is added generally consist of:

A mixture of a weak acid, the 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 corresponding salt, while taking into account:

pH range in which the buffer solution will be effective
The capacity of a solution is the amount of strong acid or strong base that can be added without affecting the pH of the solution.
No undesired reactions should occur that could change the composition of the solution