Composition name and chemical properties of bases. Bases, their classification and properties

Bases are complex compounds that include 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 valency 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 are the formulas of such substances as NaOH, Al(OH)3, Ca(OH)2.

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.

The division of the bases into groups according to various criteria is presented in table 11.

Table 11
Base classification

All bases, except for a solution of ammonia in water, are solids with different colors. For example, calcium hydroxide Ca (OH) 2 white color, copper (II) hydroxide Cu (OH) 2 blue color, nickel (II) hydroxide Ni (OH) 2 green, iron (III) Fe (OH) 3 red-brown, etc.

An aqueous solution of ammonia NH 3 H 2 O, unlike other bases, does not contain metal cations, but a complex singly charged ammonium cation NH - 4 and exists only in solution (this solution is known to you under the name ammonia). It easily decomposes into ammonia and water:

However, no matter how different the bases are, they all consist of metal ions and hydroxo groups, the number of which is equal to the oxidation state of the metal.

All bases, and first of all alkalis (strong electrolytes), form hydroxide ions OH - during dissociation, which determine the series common properties: soapiness to the touch, discoloration of indicators (litmus, methyl orange and phenolphthalein), interaction with other substances.

Typical base reactions

The first reaction (universal) was considered in § 38.

Laboratory experiment No. 23
The interaction of alkalis with acids

Write down two molecular reaction equations, the essence of which is expressed by the following ionic equation:

H + + OH - \u003d H 2 O.

Carry out the reactions, the equations of which you have made. Remember what substances (except acids and alkalis) are needed to observe these chemical reactions.

The second reaction takes place between alkalis and non-metal oxides, which correspond to acids, for example,

Corresponds

etc.

When oxides interact with bases, salts of the corresponding acids and water are formed:

Rice. 141.
The interaction of alkali with non-metal oxide

Laboratory experiment No. 24
Interaction of alkalis with oxides of non-metals

Repeat the experiment you did before. Pour 2-3 ml of a clear solution of lime water into a test tube.

Place a juice straw in it, which acts as a gas outlet tube. Gently pass exhaled air through the solution. What are you watching?

Write down the molecular and ionic equations of the reaction.

Rice. 142.
The interaction of alkalis with salts:
a - with the formation of a precipitate; b - with the formation of gas

The third reaction is a typical ion exchange reaction and only occurs if the result is a precipitate or a gas is released, for example:

Laboratory experiment No. 25
The interaction of alkalis with salts

In three tubes, pour 1-2 ml of solutions of substances in pairs: 1st tube - sodium hydroxide and ammonium chloride; 2nd tube - potassium hydroxide and iron sulfate (III); 3rd tube - sodium hydroxide and barium chloride.

Heat the contents of the 1st test tube and identify one of the reaction products by smell.

Formulate a conclusion about the possibility of interaction of alkalis with salts.

Insoluble bases decompose when heated into metal oxide and water, which is not typical for alkalis, for example:

Fe (OH) 2 \u003d FeO + H 2 O.

Laboratory experiment No. 26
Preparation and properties of insoluble bases

Pour 1 ml of copper (II) sulfate or chloride solution into two test tubes. Add 3-4 drops of sodium hydroxide solution to each tube. Describe the resulting copper(II) hydroxide.

Note. Leave the test tubes with the resulting copper (II) hydroxide for the following experiments.

Write the molecular and ionic equations for the reaction. Indicate the type of reaction based on the "number and composition of the starting materials and reaction products".

Add 1-2 ml of hydrochloric acid to one of the test tubes with copper (II) hydroxide obtained in the previous experiment. What are you watching?

Using a pipette, place 1-2 drops of the resulting solution on a glass or porcelain plate and, using crucible tongs, carefully evaporate it. Examine the crystals that form. Note their color.

Write the molecular and ionic equations for the reaction. Indicate the type of reaction based on the "number and composition of the starting materials and reaction products", "participation of a catalyst" and "reversibility of a chemical reaction".

Heat one of the test tubes with copper hydroxide obtained earlier or given by the teacher () (Fig. 143). What are you watching?

Rice. 143.
Decomposition of copper (II) hydroxide when heated

Make an equation for the reaction, indicate the condition for its occurrence and the type of reaction according to the signs "the number and composition of the starting materials and reaction products", "release or absorption of heat" and "reversibility of the chemical reaction".

Keywords and phrases

1. Base classification.
2. Typical properties of bases: their interaction with acids, non-metal oxides, salts.
3. Typical property of insoluble bases: decomposition when heated.
4. Conditions for typical base reactions.

Work with computer

1. Refer to the electronic application. Study the material of the lesson and complete the suggested tasks.
2. Search the Internet for email addresses that can serve as additional sources that reveal the content of the keywords and phrases of the paragraph. Offer the teacher your help in preparing a new lesson - make a report on the key words and phrases of the next paragraph.

Questions and tasks

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 aqueous solutions 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.

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. The general formula for bases is Me (OH) x. The metal atom is always one, 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 sodium valency is 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 can change 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 is yellow, Ni(OH) 2 is light green, Fe(OH) 3 is 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, alkaline earth metals - calcium (Ca), strontium (Sr) and barium (Ba) are among the active metals that form alkalis.

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. 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 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.

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.

Topic quiz

Report Evaluation

Average rating: 4.5. Total ratings received: 135.

Single acid (NaOH, KOH, NH 4 OH, etc.);

Two-acid (Ca (OH) 2, Cu (OH) 2, Fe (OH) 2;

Triacid (Ni (OH) 3, Co (OH) 3, Mn (OH) 3.

Classification by solubility in water and degree of ionization:

Strong bases soluble in water

for example:

alkalis - hydroxides of alkali and alkaline earth metals LiOH - lithium hydroxide, NaOH - sodium hydroxide (caustic soda), KOH - potassium hydroxide (caustic potash), Ba (OH) 2 - barium hydroxide;

Strong bases insoluble in water

for example:

Cu (OH) 2 - copper (II) hydroxide, Fe (OH) 2 - iron (II) hydroxide, Ni (OH) 3 - nickel (III) hydroxide.

Chemical properties

1. Action on indicators

Litmus - blue;

Methyl orange - yellow

Phenolphthalein - raspberry.

2. Interaction with acid oxides

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

KOH + CO 2 = KHCO 3

3. Interaction with acids (neutralization reaction)

NaOH + HNO 3 \u003d NaNO 3 + H 2 O; Cu(OH) 2 + 2HCl = CuCl 2 + 2H 2 O

4. Exchange reaction with salts

Ba(OH) 2 + K 2 SO 4 = 2KOH + BaSO 4

3KOH + Fe(NO 3) 3 = Fe(OH) 3 + 3KNO 3

5. Thermal decomposition

Cu (OH) 2 t \u003d CuO + H 2 O; 2 CuOH \u003d Cu 2 O + H 2 O

2Co (OH) 3 \u003d Co 2 O 3 + ZH 2 O; 2AgOH \u003d Ag 2 O + H 2 O

6. Hydroxides in which d-metals have low c. o., able to be oxidized by oxygen in the air,

for example:

4Fe(OH) 2 + O 2 + 2Н 2 O = 4Fe(OH) 3

2Mn(OH) 2 + O 2 + 2H 2 O = 2Mn(OH) 4

7. Alkali solutions interact with amphoteric hydroxides:

2KOH + Zn(OH) 2 = K 2

2KOH + Al 2 O 3 + ZN 2 O \u003d 2K

8. Alkali solutions interact with metals that form amphoteric oxides and hydroxides (Zn, AI, etc.),

for example:

Zn + 2 NaOH + 2H 2 O \u003d Na 2 + H 2

2AI + 2KOH + 6H 2 O \u003d 2KAl (OH) 4] + 3H 2

9. In alkali solutions, some non-metals disproportionate,

for example:

Cl 2 + 2NaOH \u003d NaCl + NaCIO + H 2 O

3S+ 6NaOH = 2Na 2 S+ Na 2 SO 3 + 3H 2 O

4P+ 3KOH + 3H 2 O = PH 3 + 3KH 2 PO 2

10. Soluble bases are widely used in alkaline hydrolysis reactions of various organic compounds(halogen derivatives of hydrocarbons, esters, fats, etc.),

for example:

C 2 H 5 CI + NaOH \u003d C 2 H 5 OH + NaCl

Methods for obtaining alkalis and insoluble bases

1. Reactions of active metals (alkali and alkaline earth metals) with water:

2Na + 2H 2 O \u003d 2 NaOH + H 2

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

2. Interaction of active metal oxides with water:

BaO + H 2 O \u003d Ba (OH) 2

3. Electrolysis of aqueous solutions of salts:

2NaCl + 2H 2 O \u003d 2NaOH + H 2 + Cl 2

CaCI 2 + 2H 2 O \u003d Ca (OH) 2 + H 2 + Cl 2

4. Precipitation from solutions of the corresponding salts with alkalis:

CuSO 4 + 2NaOH \u003d Cu (OH) 2 + Na 2 SO 4

FeCI 3 + 3KOH = Fe(OH) 3 + 3KCI