Interaction of insoluble bases. Chemical properties of bases

30.09.2019

Before discussing the chemical properties of bases and amphoteric hydroxides, let's clearly define what they are?

1) Bases or basic hydroxides include metal hydroxides in the oxidation state +1 or +2, i.e. the formulas of which are written either as MeOH or Me(OH) 2. However, there are exceptions. Thus, the hydroxides Zn(OH) 2, Be(OH) 2, Pb(OH) 2, Sn(OH) 2 are not bases.

2) Amphoteric hydroxides include metal hydroxides in the oxidation state +3, +4, as well as, as exceptions, the hydroxides Zn(OH) 2, Be(OH) 2, Pb(OH) 2, Sn(OH) 2. Metal hydroxides in oxidation state +4, in Unified State Exam assignments do not occur, so they will not be considered.

Chemical properties of bases

All grounds are divided into:

Let us remember that beryllium and magnesium are not alkaline earth metals.

In addition to being soluble in water, alkalis also dissociate very well in aqueous solutions, while insoluble bases have a low degree of dissociation.

This difference in solubility and ability to dissociate between alkalis and insoluble hydroxides leads, in turn, to noticeable differences in their chemical properties. So, in particular, alkalis are more chemically active compounds and are often able to enter into reactions that insoluble bases do not.

Interaction of bases with acids

Alkalis react with absolutely all acids, even very weak and insoluble ones. For example:

Insoluble bases react with almost all soluble acids, but do not react with insoluble silicic acid:

It should be noted that both strong and weak bases with the general formula of the form Me(OH) 2 can form basic salts when there is a lack of acid, for example:

Interaction with acid oxides

Alkalis react with all acidic oxides, forming salts and often water:

Insoluble bases are capable of reacting with all higher acid oxides corresponding to stable acids, for example, P 2 O 5, SO 3, N 2 O 5, with the formation of medium salts:

Insoluble bases of the form Me(OH) 2 react in the presence of water with carbon dioxide exclusively with the formation of basic salts. For example:

Cu(OH) 2 + CO 2 = (CuOH) 2 CO 3 + H 2 O

Due to its exceptional inertness, only the strongest bases, alkalis, react with silicon dioxide. In this case, normal salts are formed. The reaction does not occur with insoluble bases. For example:

Interaction of bases with amphoteric oxides and hydroxides

All alkalis react with amphoteric oxides and hydroxides. If the reaction is carried out by fusing an amphoteric oxide or hydroxide with a solid alkali, this reaction leads to the formation of hydrogen-free salts:

If aqueous solutions of alkalis are used, then hydroxo complex salts are formed:

In the case of aluminum, under the action of an excess of concentrated alkali, instead of Na salt, Na 3 salt is formed:

Interaction of bases with salts

Any base reacts with any salt only if two conditions are met simultaneously:

1) solubility of the starting compounds;

2) the presence of precipitate or gas among the reaction products

For example:

Thermal stability of substrates

All alkalis, except Ca(OH) 2, are resistant to heat and melt without decomposition.

All insoluble bases, as well as slightly soluble Ca(OH) 2, decompose when heated. Most high temperature decomposition of calcium hydroxide – about 1000 o C:

Insoluble hydroxides have much lower decomposition temperatures. For example, copper (II) hydroxide decomposes already at temperatures above 70 o C:

Chemical properties of amphoteric hydroxides

Interaction of amphoteric hydroxides with acids

Amphoteric hydroxides react with strong acids:

Amphoteric metal hydroxides in the oxidation state +3, i.e. type Me(OH) 3, do not react with acids such as H 2 S, H 2 SO 3 and H 2 CO 3 due to the fact that the salts that could be formed as a result of such reactions are subject to irreversible hydrolysis to the original amphoteric hydroxide and corresponding acid:

Interaction of amphoteric hydroxides with acid oxides

Amphoteric hydroxides react with higher oxides, which correspond to stable acids (SO 3, P 2 O 5, N 2 O 5):

Amphoteric metal hydroxides in the oxidation state +3, i.e. type Me(OH) 3, do not react with acidic oxides SO 2 and CO 2.

Interaction of amphoteric hydroxides with bases

Of the bases, amphoteric hydroxides react only with alkalis. In this case, if an aqueous solution of alkali is used, then hydroxo complex salts are formed:

And when amphoteric hydroxides are fused with solid alkalis, their anhydrous analogues are obtained:

Interaction of amphoteric hydroxides with basic oxides

Amphoteric hydroxides react when fused with oxides of alkali and alkaline earth metals:

Thermal decomposition of amphoteric hydroxides

All amphoteric hydroxides are insoluble in water and, like any insoluble hydroxides, decompose when heated into the corresponding oxide and water.

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, has a solution white. 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.

The division of bases into groups according to various characteristics is presented in Table 11.

Table 11
Classification of bases

All bases, except a solution of ammonia in water, are solid substances of different colors. For example, calcium hydroxide Ca(OH) 2 is white, copper (II) hydroxide Cu(OH) 2 blue color, nickel (II) hydroxide Ni(OH) 2 green, iron (III) hydroxide 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 (you know this solution as 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, especially alkalis ( strong electrolytes), form upon dissociation hydroxide ions OH - , which determine the series general properties: soapiness to the touch, change in color 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
Interaction of alkalis with acids

H + + OH - = H 2 O.

Carry out the reactions for which you have created equations. Remember what substances (except acid and alkali) are needed to observe these chemical reactions.

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

Compliant

etc.

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

Rice. 141.
Interaction of alkali with non-metal oxide

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

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 vent pipe. Gently pass exhaled air through the solution. What are you observing?

Write down the molecular and ionic equations for the reaction.

Rice. 142.
Interaction of alkalis with salts:
a - with the formation of sediment; b - with gas formation

The third reaction is a typical ion exchange reaction and only occurs if it results in a precipitate or gas being released, for example:

Laboratory experiment No. 25
Interaction of alkalis with salts

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 = 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 test tube. Describe the copper(II) hydroxide formed.

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

Write down the molecular and ionic equations for the reaction. Indicate the type of reaction based on the “number and composition of starting substances and reaction products.”

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

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 down the molecular and ionic equations for the reaction. Indicate the type of reaction based on “the number and composition of 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 observing?

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

Draw up an equation for the reaction carried out, indicate the condition for its occurrence and the type of reaction based on the characteristics “number and composition of starting substances and reaction products”, “release or absorption of heat” and “reversibility of a chemical reaction”.

Key words and phrases

Classification of bases.
Typical properties of bases: their interaction with acids, non-metal oxides, salts.
A typical property of insoluble bases is decomposition when heated.
Conditions for typical base reactions.

Working with a computer

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

Questions and tasks

a) obtaining grounds.

1) The general method for preparing bases is an exchange reaction, with the help of which both insoluble and soluble bases can be obtained:

CuSO 4 + 2 KOH = Cu(OH) 2  + K 2 SO 4,

K 2 CO 3 + Ba(OH) 2 = 2KOH + BaCO 3 .

When soluble bases are obtained by this method, an insoluble salt precipitates.

2) Alkalis can also be obtained by reacting alkali and alkaline earth metals or their oxides with water:

2Li + 2H 2 O = 2LiOH + H 2,

SrO + H 2 O = Sr(OH) 2.

3) Alkalis in technology are usually obtained by electrolysis of aqueous solutions of chlorides:

b)chemicalproperties of bases.

1) The most characteristic reaction of bases is their interaction with acids - the neutralization reaction. Both alkalis and insoluble bases enter into it:

NaOH + HNO 3 = NaNO 3 + H 2 O,

Cu(OH) 2 + H 2 SO 4 = CuSO 4 + 2 H 2 O.

2) It was shown above how alkalis interact with acidic and amphoteric oxides.

3) When alkalis interact with soluble salts, a new salt and a new base are formed. Such a reaction proceeds to completion only when at least one of the resulting substances precipitates.

FeCl 3 + 3 KOH = Fe(OH) 3  + 3 KCl

4) When heated, most bases, with the exception of alkali metal hydroxides, decompose into the corresponding oxide and water:

2 Fe(OH) 3 = Fe 2 O 3 + 3 H 2 O,

Ca(OH) 2 = CaO + H 2 O.

ACIDS – complex substances whose molecules consist of one or more hydrogen atoms and an acid residue. The composition of acids can be expressed by the general formula H x A, where A is the acid residue. Hydrogen atoms in acids can be replaced or exchanged with metal atoms, resulting in the formation of salts.

If an acid contains one such hydrogen atom, then it is a monobasic acid (HCl - hydrochloric, HNO 3 - nitric, HСlO - hypochlorous, CH 3 COOH - acetic); two hydrogen atoms - dibasic acids: H 2 SO 4 - sulfuric, H 2 S - hydrogen sulfide; three hydrogen atoms are tribasic: H 3 PO 4 – orthophosphoric, H 3 AsO 4 – orthoarsenic.

Depending on the composition of the acid residue, acids are divided into oxygen-free (H 2 S, HBr, HI) and oxygen-containing (H 3 PO 4, H 2 SO 3, H 2 CrO 4). In molecules of oxygen-containing acids, hydrogen atoms are connected through oxygen to the central atom: H – O – E. The names of oxygen-free acids are formed from the root of the Russian name for a non-metal, the connecting vowel - O- and the words “hydrogen” (H 2 S – hydrogen sulfide). The names of oxygen-containing acids are given as follows: if a non-metal (less often a metal) that is part of the acid residue is in highest degree oxidation, then suffixes are added to the root of the Russian name of the element -n-, -ev-, or - ov- and then the ending -aya-(H 2 SO 4 - sulfur, H 2 CrO 4 - chrome). If the oxidation state of the central atom is lower, then the suffix is used -ist-(H 2 SO 3 – sulfurous). If a non-metal forms a number of acids, other suffixes are used (HClO - chlorine ovatist aya, HClO 2 – chlorine ist aya, HClO 3 – chlorine ovat aya, HClO 4 – chlorine n aya).

WITH
From the point of view of the theory of electrolytic dissociation, acids are electrolytes that dissociate in an aqueous solution to form only hydrogen ions as cations:

N x A xN + +A x-

The presence of H + ions causes a change in the color of indicators in acid solutions: litmus (red), methyl orange (pink).

Preparation and properties of acids

A) production of acids.

1) Oxygen-free acids can be obtained by directly combining non-metals with hydrogen and then dissolving the corresponding gases in water:

2) Oxygen-containing acids can often be obtained by reacting acid oxides with water.

3) Both oxygen-free and oxygen-containing acids can be obtained by exchange reactions between salts and other acids:

BaBr 2 + H 2 SO 4 = BaSO 4 + 2 HBr,

CuSO 4 + H 2 S = H 2 SO 4 + CuS ,

FeS+ H 2 SO 4 (dissolved) = H 2 S + FeSO 4,

NaCl (solid) + H 2 SO 4 (conc.) = HCl  + NaHSO 4,

AgNO 3 + HCl = AgCl  + HNO 3,

4) In some cases, redox reactions can be used to produce acids:

3P + 5HNO 3 + 2H 2 O = 3H 3 PO 4 + 5NO 

b ) chemical properties of acids.

1) Acids interact with bases and amphoteric hydroxides. In this case, practically insoluble acids (H 2 SiO 3, H 3 BO 3) can only react with soluble alkalis.

H 2 SiO 3 +2NaOH=Na 2 SiO 3 +2H 2 O

2) The interaction of acids with basic and amphoteric oxides is discussed above.

3) The interaction of acids with salts is an exchange reaction with the formation of salt and water. This reaction proceeds to completion if the reaction product is an insoluble or volatile substance, or a weak electrolyte.

Ni 2 SiO 3 +2HCl=2NaCl+H 2 SiO 3

Na 2 CO 3 +H 2 SO 4 =Na 2 SO 4 +H 2 O+CO 2 

4) The interaction of acids with metals is an oxidation-reduction process. Reductant - metal, oxidizing agent - hydrogen ions (non-oxidizing acids: HCl, HBr, HI, H 2 SO 4 (diluted), H 3 PO 4) or an anion of the acid residue (oxidizing acids: H 2 SO 4 (conc), HNO 3(end and break)). The reaction products of the interaction of non-oxidizing acids with metals in the voltage series up to hydrogen are salt and hydrogen gas:

Zn+H 2 SO 4(dil) =ZnSO 4 +H 2 

Zn+2HCl=ZnCl 2 +H 2 

Oxidizing acids interact with almost all metals, including low-active ones (Cu, Hg, Ag), and the products of reduction of the acid anion, salt and water are formed:

Cu + 2H 2 SO 4 (conc.) = CuSO 4 + SO 2  + 2 H 2 O,

Pb + 4HNO 3(conc) = Pb(NO 3) 2 +2NO 2 + 2H 2 O

AMPHOTERIC HYDROXIDES exhibit acid-base duality: they react with acids as bases:

2Cr(OH) 3 + 3H 2 SO 4 = Cr 2 (SO 4) 3 + 6H 2 O,

and with bases - like acids:

Cr(OH) 3 + NaOH = Na (the reaction takes place in an alkali solution);

Cr(OH) 3 + NaOH = NaCrO 2 + 2H 2 O (the reaction occurs between solid substances during fusion).

Amphoteric hydroxides form salts with strong acids and bases.

Like other insoluble hydroxides, amphoteric hydroxides decompose when heated into oxide and water:

Be(OH) 2 = BeO+H 2 O.

SALT– ionic compounds consisting of metal cations (or ammonium) and anions of acid residues. Any salt can be considered as a product of the reaction of neutralization of a base with an acid. Depending on the ratio of acid and base, salts are obtained: average(ZnSO 4, MgCl 2) – the product of complete neutralization of the base with acid, sour(NaHCO 3, KH 2 PO 4) - with excess acid, basic(CuOHCl, AlOHSO 4) – with an excess of base.

The names of salts according to the international nomenclature are formed from two words: the name of the acid anion in the nominative case and the metal cation in the genitive case, indicating the degree of its oxidation, if it is variable, with a Roman numeral in parentheses. For example: Cr 2 (SO 4) 3 – chromium (III) sulfate, AlCl 3 – aluminum chloride. The names of acid salts are formed by adding the word hydro- or dihydro-(depending on the number of hydrogen atoms in the hydroanion): Ca(HCO 3) 2 - calcium bicarbonate, NaH 2 PO 4 - sodium dihydrogen phosphate. The names of the main salts are formed by adding the words hydroxo- or dihydroxo-: (AlOH)Cl 2 – aluminum hydroxychloride, 2 SO 4 – chromium(III) dihydroxosulfate.

Preparation and properties of salts

A ) chemical properties of salts.

1) The interaction of salts with metals is an oxidation-reduction process. In this case, the metal located to the left in the electrochemical series of voltages displaces the subsequent ones from solutions of their salts:

Zn+CuSO 4 =ZnSO 4 +Cu

Alkali and alkaline earth metals do not use for the reduction of other metals from aqueous solutions of their salts, since they interact with water, displacing hydrogen:

2Na+2H 2 O=H 2 +2NaOH.

2) The interaction of salts with acids and alkalis was discussed above.

3) The interaction of salts with each other in solution occurs irreversibly only if one of the products is a slightly soluble substance:

BaCl 2 + Na 2 SO 4 = BaSO 4  + 2NaCl.

4) Hydrolysis of salts - exchange decomposition of some salts with water. The hydrolysis of salts will be discussed in detail in the topic “electrolytic dissociation”.

b) methods of obtaining salts.

In laboratory practice, the following methods for obtaining salts are usually used, based on the chemical properties of various classes of compounds and simple substances:

1) Interaction of metals with non-metals:

Cu+Cl 2 = CuCl 2,

2) Interaction of metals with salt solutions:

Fe+CuCl 2 =FeCl 2 +Cu.

3) Interaction of metals with acids:

Fe+2HCl=FeCl 2 +H 2 .

4) Interaction of acids with bases and amphoteric hydroxides:

3HCl+Al(OH) 3 =AlCl 3 +3H 2 O.

5) Interaction of acids with basic and amphoteric oxides:

2HNO 3 +CuO=Cu(NO 3) 2 +2H 2 O.

6) Interaction of acids with salts:

HCl+AgNO 3 =AgCl+HNO 3.

7) Interaction of alkalis with salts in solution:

3KOH+FeCl 3 =Fe(OH) 3 +3KCl.

8) Interaction of two salts in solution:

NaCl + AgNO 3 = NaNO 3 + AgCl.

9) Interaction of alkalis with acidic and amphoteric oxides:

Ca(OH) 2 +CO 2 =CaCO 3 +H 2 O.

10) Interaction of oxides of various types with each other:

CaO+CO 2 = CaCO 3.

Salts are found in nature in the form of minerals and rocks, in a dissolved state in the water of oceans and seas.

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 valence 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 valency of aluminum is III.

The number of hydroxyl groups can vary in compounds with metals of variable valency. For example, Fe(OH) 2 and Fe(OH) 3. In such cases, the valency 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 has yellow, Ni(OH) 2 - light green, Fe(OH) 3 - red-brown.

Rice. 1. Alkalis in solid state.

Species

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 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

Grounds get 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.

*Reactions*	*What is formed*	*Examples*
With acids	Salt and water. Insoluble bases react only with soluble acids	Cu(OH) 2 ↓ + H 2 SO 4 → CuSO 4 +2H 2 O
High temperature decomposition	Metal oxide and water	2Fe(OH) 3 → Fe 2 O 3 + 3H 2 O
With acid 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 ↓
Alkalis with some metals	Complex salt and hydrogen	2Al + 2NaOH + 6H 2 O → 2Na + 3H 2

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.