Solubility of salts in water at room temperature. Why do salts dissolve in water? Solubility of acids in water table

Water is one of the main chemical compounds on our planet. One of its most interesting properties is the ability to form aqueous solutions. And in many areas of science and technology, the solubility of salt in water plays an important role.

Solubility refers to the ability various substances form with liquids - solvents - homogeneous (homogeneous) mixtures. It is the volume of the material that is used to dissolve and form a saturated solution that determines its solubility, comparable to the mass fraction of this substance or its amount in a concentrated solution.

According to their ability to dissolve, salts are classified as follows:

soluble substances include substances that can be dissolved in 100 g of water more than 10 g;
sparingly soluble are those whose amount in the solvent does not exceed 1 g;
the concentration of insoluble in 100 g of water is less than 0.01.

In the case when the polarity of the substance used for dissolution is similar to the polarity of the solvent, it is soluble. At different polarities, most likely, it is not possible to dilute the substance.

How dissolution occurs

If we talk about whether salt dissolves in water, then for most salts this is a fair statement. There is a special table according to which you can accurately determine the amount of solubility. Since water is a universal solvent, it mixes well with other liquids, gases, acids and salts.

One of the most good examples dissolution of a solid in water can be observed almost every day in the kitchen, during the preparation of dishes using table salt. So why does salt dissolve in water?

From school course Chemistry, many remember that the molecules of water and salt are polar. This means that their electrical poles are opposite, which results in a high dielectric constant. Water molecules surround ions of another substance, for example, as in our case, NaCl. In this case, a liquid is formed, which is homogeneous in its consistency.

Temperature effect

There are several factors that affect the solubility of salts. First of all, this is the temperature of the solvent. The higher it is, the greater is the value of the diffusion coefficient of particles in the liquid, and the mass transfer occurs faster.

Although, for example, the solubility of common salt (NaCl) in water practically does not depend on temperature, since its solubility coefficient is 35.8 at t 20 ° C and 38.0 at 78 ° C. But copper sulfate (CaSO4) with increasing temperature water dissolves worse.

Other factors that affect solubility include:

The size of the dissolved particles - with a larger area of phase separation, the dissolution occurs faster.
A mixing process that, when performed intensively, contributes to a more efficient mass transfer.
The presence of impurities: some accelerate the dissolution process, while others, hindering diffusion, reduce the rate of the process.

Video about the mechanism of salt dissolution

Definition salts within the framework of the theory of dissociation. Salts are usually divided into three groups: medium, sour and basic. In medium salts, all hydrogen atoms of the corresponding acid are replaced by metal atoms, in acid salts they are only partially replaced, in basic salts of the OH group of the corresponding base they are partially replaced by acid residues.

There are also some other types of salts, such as double salts, which contain two different cations and one anion: CaCO 3 MgCO 3 (dolomite), KCl NaCl (sylvinite), KAl (SO 4) 2 (potassium alum); mixed salts, which contain one cation and two different anions: CaOCl 2 (or Ca(OCl)Cl); complex salts, which include complex ion, consisting of a central atom linked to several ligands: K 4 (yellow blood salt), K 3 (red blood salt), Na, Cl; hydrated salts(crystal hydrates), which contain molecules water of crystallization: CuSO 4 5H 2 O( blue vitriol), Na 2 SO 4 10H 2 O (Glauber's salt).

The name of the salts is formed from the name of the anion followed by the name of the cation.

For salts of oxygen-free acids, a suffix is added to the name of the non-metal id, e.g. sodium chloride NaCl, iron(H) sulfide FeS, etc.

When naming salts of oxygen-containing acids, in the case of higher oxidation states, the ending is added to the Latin root of the name of the element — am, in the case of lower oxidation states, the ending -it. In the names of some acids, the prefix is used to designate the lowest oxidation states of a non-metal hypo-, for salts of perchloric and permanganic acids, use the prefix per-, ex: calcium carbonate CaCO 3, iron (III) sulfate Fe 2 (SO 4) 3, iron (II) sulfite FeSO 3, potassium hypochlorite KOSl, potassium chlorite KOSl 2, potassium chlorate KOSl 3, potassium perchlorate KOSl 4, potassium permanganate KMnO 4, potassium dichromate K 2 Cr 2 O 7 .

Acid and basic salts can be considered as a product of incomplete conversion of acids and bases. According to the international nomenclature, the hydrogen atom, which is part of the acid salt, is denoted by the prefix hydro-, OH group - prefix hydroxy, NaHS - sodium hydrosulfide, NaHSO 3 - sodium hydrosulfite, Mg (OH) Cl - magnesium hydroxychloride, Al (OH) 2 Cl - aluminum dihydroxy chloride.

In the names of complex ions, ligands are first indicated, followed by the name of the metal, indicating the corresponding oxidation state (Roman numerals in brackets). In the names of complex cations, Russian names of metals are used, for example: Cl 2 - tetraammine copper (P) chloride, 2 SO 4 - diammine silver (1) sulfate. In the names of complex anions, the Latin names of metals with the suffix -at are used, for example: K[Al(OH) 4 ] - potassium tetrahydroxyaluminate, Na - sodium tetrahydroxychromate, K 4 - potassium hexacyanoferrate (H) .

Names of hydrated salts (crystalline hydrates) are formed in two ways. You can use the complex cation naming system described above; for example, copper sulfate SO 4 H 2 0 (or CuSO 4 5H 2 O) can be called tetraaquacopper(II) sulfate. However, for the most well-known hydrated salts, most often the number of water molecules (the degree of hydration) is indicated by a numerical prefix to the word "hydrate", for example: CuSO 4 5H 2 O - copper (I) sulfate pentahydrate, Na 2 SO 4 10H 2 O - sodium sulfate decahydrate, CaCl 2 2H 2 O - calcium chloride dihydrate.

Solubility of salts

According to their solubility in water, salts are divided into soluble (P), insoluble (H) and slightly soluble (M). To determine the solubility of salts, use the table of the solubility of acids, bases and salts in water. If there is no table at hand, then you can use the rules. They are easy to remember.

1. All salts of nitric acid are soluble - nitrates.

2. All salts of hydrochloric acid are soluble - chlorides, except for AgCl (H), PbCl 2 (M).

3. All salts of sulfuric acid - sulfates are soluble, except for BaSO 4 (H), PbSO 4 (H).

4. Sodium and potassium salts are soluble.

5. All phosphates, carbonates, silicates and sulfides do not dissolve, except for Na salts + and K + .

Of all chemical compounds, salts are the most numerous class of substances. These are solids, they differ from each other in color and solubility in water. IN early XIX V. Swedish chemist I. Berzelius formulated the definition of salts as reaction products of acids with bases or compounds obtained by replacing hydrogen atoms in an acid with a metal. On this basis, salts are distinguished as medium, acidic and basic. Medium, or normal, salts are products of the complete replacement of hydrogen atoms in an acid with a metal.

For example:

Na 2 CO 3 - sodium carbonate;

CuSO 4 - copper (II) sulfate, etc.

Such salts dissociate into metal cations and anions of the acid residue:

Na 2 CO 3 \u003d 2Na + + CO 2 -

Acid salts are products of incomplete replacement of hydrogen atoms in an acid by a metal. Acid salts include, for example, baking soda NaHCO 3 , which consists of a metal cation Na + and an acidic singly charged residue HCO 3 - . For an acidic calcium salt, the formula is written as follows: Ca (HCO 3) 2. The names of these salts are made up of the names of medium salts with the addition of the prefix hydro- , For example:

Mg (HSO 4) 2 - magnesium hydrosulfate.

Dissociate acid salts as follows:

NaHCO 3 \u003d Na + + HCO 3 -
Mg (HSO 4) 2 \u003d Mg 2+ + 2HSO 4 -

Basic salts are products of incomplete substitution of hydroxo groups in the base for an acid residue. For example, such salts include the famous malachite (CuOH) 2 CO 3, which you read about in the works of P. Bazhov. It consists of two basic cations CuOH + and a doubly charged anion of the acid residue CO 3 2- . The CuOH + cation has a +1 charge, therefore, in the molecule, two such cations and one doubly charged CO 3 2- anion are combined into an electrically neutral salt.

The names of such salts will be the same as for normal salts, but with the addition of the prefix hydroxo-, (CuOH) 2 CO 3 - copper (II) hydroxocarbonate or AlOHCl 2 - aluminum hydroxochloride. Most basic salts are insoluble or sparingly soluble.

The latter dissociate like this:

AlOHCl 2 \u003d AlOH 2 + + 2Cl -

Salt properties

The first two exchange reactions have been discussed in detail previously.

The third reaction is also an exchange reaction. It flows between salt solutions and is accompanied by the formation of a precipitate, for example:

The fourth reaction of salts is associated with the position of the metal in the electrochemical series of metal voltages (see "Electrochemical series of metal voltages"). Each metal displaces from salt solutions all other metals located to the right of it in a series of voltages. This is subject to the following conditions:

1) both salts (both reacting and formed as a result of the reaction) must be soluble;

2) metals should not interact with water, therefore, metals of the main subgroups of groups I and II (for the latter, starting with Ca) do not displace other metals from salt solutions.

Methods for obtaining salts

Ways to get and Chemical properties salts. Salts can be obtained from inorganic compounds of almost any class. Along with these methods, salts of anoxic acids can be obtained by direct interaction of a metal and a non-metal (Cl, S, etc.).

Many salts are stable when heated. However, ammonium salts, as well as some salts of low-active metals, weak acids and acids in which elements exhibit higher or lower oxidation states, decompose when heated.

CaCO 3 \u003d CaO + CO 2

2Ag 2 CO 3 \u003d 4Ag + 2CO 2 + O 2

NH 4 Cl \u003d NH 3 + HCl

2KNO 3 \u003d 2KNO 2 + O 2

2FeSO 4 \u003d Fe 2 O 3 + SO 2 + SO 3

4FeSO 4 \u003d 2Fe 2 O 3 + 4SO 2 + O 2

2Cu(NO 3) 2 \u003d 2CuO + 4NO 2 + O 2

2AgNO 3 \u003d 2Ag + 2NO 2 + O 2

NH 4 NO 3 \u003d N 2 O + 2H 2 O

(NH 4) 2 Cr 2 O 7 \u003d Cr 2 O 3 + N 2 + 4H 2 O

2KSlO 3 \u003d MnO 2 \u003d 2KCl + 3O 2

4KClO 3 \u003d 3KSlO 4 + KCl

Solubility table chemical elements- this is a table with the solubilities in water of the most famous inorganic acids, bases and salts.

Definition 1

The chemistry solubility table shows the solubility at 20 °C, with increasing temperature the solubility increases.

A substance is soluble in water if its solubility is greater than 1 g in 100 g of water and insoluble if less than 0.1 g / 100 g. For example, finding lithium in a solubility table in chemistry, you can make sure that almost all of its salts form solutions.

On fig. 1 and fig. 2 presented photos complete table solubility in chemistry with the names of acid residues.

Figure 1. Photo table of solubility in chemistry 2018-2019

Figure 2. Chemistry table with acids and acid residues

To make up the name of the salt, you must use the periodic table and solubility. The name of the metal from the periodic table is added to the name of the acid residue, for example:

$\mathrm(Zn_3(PO_4)_2)$ - zinc phosphate; $\mathrm(FeSO_4)$ - iron(II) sulfate.

In brackets with a text name, it is necessary to indicate the valency of the metal, if there are several of them. In the case of iron, there is also $\mathrm(Fe_2(SO_4)_3)$ salt - iron(III) sulfate.

What can be learned using the solubility table in chemistry

The table of solubility of substances in chemistry with precipitation is used to determine the possibility of a reaction occurring, since the formation of a precipitate or gas is necessary for the irreversible course of the reaction.

The solubility table of salts, acids and bases is the foundation, without which it is impossible to fully master chemical knowledge. The solubility of bases and salts helps in teaching not only schoolchildren, but also professional people. The creation of many life products cannot do without this knowledge.

Table of solubility of acids, salts and bases in water

The table of solubility of salts and bases in water is a guide that helps in mastering chemical bases. The following notes will help you understand the table below.

P - indicates a soluble substance;
H is an insoluble substance;
M - the substance is slightly soluble in the aquatic environment;
RK - a substance can dissolve only when exposed to strong organic acids;
The dash will say that such a creature does not exist in nature;
NK - does not dissolve in either acids or water;
? - a question mark indicates that today there is no exact information about the dissolution of the substance.

Often, the table is used by chemists and schoolchildren, students for laboratory research, during which it is necessary to establish the conditions for the occurrence of certain reactions. According to the table, it turns out to find out how the substance behaves in a hydrochloric or acidic environment, whether a precipitate is possible. Precipitate during research and experiments indicates the irreversibility of the reaction. This is a significant point that can affect the course of the entire laboratory work.