Bases interact with metals. Chemical properties of insoluble bases

The bases are complex connections, including two main structural components:

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

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

The only exception to general rule base formation should be considered when the hydroxo group is attached not to the metal, but to the 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 valence of the hydroxo group is equal to one, respectively, the number of these groups in the molecule will directly depend on what valency the metals that enter into the reaction have. Examples in this case the formulas of such substances as NaOH, Al (OH) 3, Ca (OH) 2 can serve.

Chemical properties 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 a certain indicator to their solution. In this case, it will noticeably change its color: for example, it will become blue from white, and phenolphthalein will become crimson.

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

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

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

metal and hydroxyl group(IS HE). 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 solution white color. 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.

DEFINITION

Hydroxides called complex substances, which include metal atoms connected to one or more hydroxo groups.

Most bases are solids with varying solubility in water. Copper(II) hydroxide blue color(Fig. 1), iron (III) hydroxide is brown, most of the others are white.

Rice. 1. Copper (II) hydroxide. Appearance.

Obtaining hydroxides

Soluble bases (alkalis) in the laboratory can be obtained by the interaction of active metals and their oxides with water:

CaO + H 2 O \u003d Ca (OH) 2.

The alkalis sodium hydroxide and calcium hydroxide are obtained by electrolysis of aqueous solutions of sodium chloride and potassium chloride.

Water-insoluble bases are obtained by the reaction of salts with alkalis in aqueous solutions:

FeCl 3 + 3NaOH aq \u003d Fe (OH) 3 ↓ + 3NaCl.

Chemical properties of hydroxides

Soluble and insoluble bases have a common property: they react with acids to form salts and water (neutralization reaction):

NaOH + HCl \u003d NaCl + H 2 O;

Cu(OH) 2 + 2HCl = CuCl 2 + H 2 O.

Alkali solutions change the color of some substances - litmus, phenolphthalein and methyl orange, called indicators (Table 1).

Table 1. Color change of indicators under the influence of solutions of acids and bases.

In addition to the general properties, alkalis and water-insoluble bases also have specific ones. For example, when a blue precipitate of copper (II) hydroxide is heated, a black substance is formed - this is copper (II) oxide:

Cu (OH) 2 \u003d CuO + H 2 O.

Alkalis, unlike insoluble bases, usually do not decompose when heated. Their solutions act on indicators, corrode organic matter, react with salt solutions (if they contain a metal capable of forming an insoluble base) and acid oxides:

Fe 2 (SO 4) 3 + 6KOH \u003d 2Fe (OH) 3 ↓ + 3K 2 SO 4;

2KOH + CO 2 \u003d K 2 CO 3 + H 2 O.

Application of hydroxides

Hydroxides are widely used in industry and everyday life. For example, great importance has calcium hydroxide. It is a white loose powder. When mixed with water, the so-called milk of lime is formed. Since calcium hydroxide is slightly soluble in water, after filtering the milk of lime, a clear solution is obtained - lime water, which becomes cloudy when carbon dioxide is passed through it. Slaked lime is used to prepare the Bordeaux mixture - a means of combating plant diseases and pests. Lime milk is widely used in chemical industry, for example, in the production of sugar, soda and other substances.

Sodium hydroxide is used for oil refining, soap production, and in the textile industry. Potassium hydroxide and lithium hydroxide are used in batteries.

Examples of problem solving

EXAMPLE 1

Exercise	In one of the tin hydroxides, the mass fraction of elements is equal to: tin - 63.6%; oxygen - 34.2%; hydrogen - 2.2%. Determine the formula for this hydroxide.
Decision	Mass fraction element X in a molecule of composition HX is calculated by the following formula: ω (X) = n × Ar (X) / M (HX) × 100%. Let us denote the number of moles of elements that make up the compound by "x" (tin), "y" (oxygen) and "z" (hydrogen). Then, the molar ratio will look like this (values ​​of relative atomic masses taken from the Periodic Table of D.I. Mendeleev, rounded up to integers): x:y:z = ω(Sn)/Ar(Sn) : ω(O)/Ar(O) : ω(H)/Ar(H); x:y:z = 63.6/119: 34.2/16: 2.1/1; x:y:z = 0.53: 2.14: 2.1 = 1: 4: 4. So the formula of tin hydroxide is Sn(OH) 4 .
Answer	The formula of tin hydroxide is Sn(OH) 4

EXAMPLE 2

Exercise	Determine the mass fraction of barium hydroxide in a solution obtained by mixing water with a mass of 50 g and barium oxide with a mass of 1.2 g.
Decision	The mass fraction of substance X in solution is calculated by the following formula: ω (X) = m(X) / m solution × 100%. The mass of the solution is the sum of the masses of the solute and the solvent: m solution = m(H 2 O) + m(BaO) = 50 + 1.2 = 51.2 g. We write the reaction equation for obtaining barium hydroxide: BaO + H 2 O \u003d Ba (OH) 2. Calculate the number of moles of starting materials: n(H 2 O) = m(H 2 O) / M(H 2 O); M(H 2 O) = 18 g/mol; n(H 2 O) \u003d 50/18 \u003d 2.8 mol. n(BaO) = m(BaO) / M(BaO); M(BaO) = 153 g/mol; n(BaO) \u003d 1.2 / 153 \u003d 0.008 mol. The calculation is carried out for a compound that is in short supply (barium oxide). According to the equation n(BaO) :n(Ba(OH) 2) = 1:1, i.e. n (Ba (OH) 2) \u003d n (BaO) \u003d 1.04 mol. Then the mass of barium hydroxide formed will be equal to: m (Ba (OH) 2) \u003d n (Ba (OH) 2) × M (Ba (OH) 2); M (Ba (OH) 2) \u003d 171 g / mol; m (Ba (OH) 2) \u003d 0.008 × 171 \u003d 1.368 g. Find the mass fraction of barium hydroxide in solution: ω (Ba (OH) 2) \u003d 1.368 / 51.2 × 100% \u003d 2.67%.
Answer	The mass fraction of barium hydroxide is 2.67%

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

Structure

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

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

Physical Properties

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

Rice. 1. Alkalis in the solid state.

Kinds

Foundations are classified according to two criteria:

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

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

These elements form the following foundations:

• 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 insoluble.

In another way, alkalis are called strong bases, and insoluble ones are called weak bases. At electrolytic dissociation alkalis quickly give up the hydroxyl group and react faster with other substances. Insoluble or weak bases less active, because don't donate a hydroxyl group.

Rice. 2. Classification of bases.

A special place in the systematization of inorganic substances is occupied by amphoteric hydroxides. They interact with both acids and bases, i.e. behave like an alkali or an acid depending on the conditions. These include Zn(OH) 2 , Al(OH) 3 , Pb(OH) 2 , Cr(OH) 3 , Be(OH) 2 and other bases.

Receipt

Grounds get different ways. The simplest is the interaction of metal with water:

Ba + 2H 2 O → Ba (OH) 2 + H 2.

Alkalis are obtained as a result of the interaction of 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.

Reactions	What is formed	Examples
With acids	Salt and water. Insoluble bases only react with soluble acids.	Cu(OH) 2 ↓ + H 2 SO 4 → CuSO 4 + 2H 2 O
Decomposition at high temperature	metal oxide and water	2Fe(OH) 3 → Fe 2 O 3 + 3H 2 O
With acidic oxides (alkalis react)		NaOH + CO 2 → NaHCO 3
With non-metals (alkalis enter)	Salt and hydrogen	2NaOH + Si + H 2 O → Na 2 SiO 3 + H 2
Exchange with salts	hydroxide and salt	Ba(OH) 2 + Na 2 SO 4 → 2NaOH + BaSO 4 ↓
Alkalines with some metals	Complex salt and hydrogen	2Al + 2NaOH + 6H 2 O → 2Na + 3H 2

With the help of 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. The reaction of indicators to the grounds.

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 an OH hydroxyl group. They are divided into soluble or alkaline and insoluble. Alkalis are more aggressive bases that quickly react 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 decompose at high temperatures.

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General properties bases are due to the presence in their solutions of the OH - ion, which creates an alkaline environment in the solution (phenolphthalein turns crimson, methyl orange - yellow, litmus - 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, under the action of alkali on a soluble salt, a precipitate precipitates or 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(crystal)®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 upon heating. Insoluble bases, when heated, decompose into a basic oxide and water:

Cu(OH) 2 ®CuO+H 2 O

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All topics in this section:

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

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Obtaining acid salts
An 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

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