a) getting a reason.
1) A common method for obtaining bases is the exchange reaction, with which both insoluble and soluble bases can be obtained:
CuSO 4 + 2 KOH \u003d Cu (OH) 2 + K 2 SO 4,
K 2 CO 3 + Ba (OH) 2 \u003d 2KOH + VaCO 3 .
When soluble bases are obtained by this method, an insoluble salt precipitates.
2) Alkalis can also be obtained by the interaction of alkali and alkaline earth metals or their oxides with water:
2Li + 2H 2 O \u003d 2LiOH + H 2,
SrO + H 2 O \u003d Sr (OH) 2.
3) Alkalis in technology are usually obtained by electrolysis of aqueous solutions of chlorides:
b)chemicalbase properties.
1) The most characteristic reaction of bases is their interaction with acids - the neutralization reaction. It includes both alkalis and insoluble bases:
NaOH + HNO 3 \u003d NaNO 3 + H 2 O,
Cu (OH) 2 + H 2 SO 4 \u003d СuSO 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 goes to completion only when at least one of the resulting substances precipitates.
FeCl 3 + 3 KOH \u003d 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 \u003d Fe 2 O 3 + 3 H 2 O,
Ca (OH) 2 \u003d CaO + H 2 O.
ACID - 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 for metal atoms, and salts are formed.
If the acid contains one such hydrogen atom, then it is a monobasic acid (HCl - hydrochloric, HNO 3 - nitric, HClO - 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 anoxic (H 2 S, HBr, HI) and oxygen-containing (H 3 PO 4, H 2 SO 3, H 2 CrO 4). In the 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 of the non-metal, the connecting vowel - about- and the words "hydrogen" (H 2 S - hydrogen sulfide). The names of oxygen-containing acids are given as follows: if the non-metal (less often the metal) that is part of the acid residue is in the highest degree of oxidation, then suffixes are added to the root of the Russian name of the element -n-, -ev-, or - ov- and then ending -and I-(H 2 SO 4 - sulfuric, H 2 CrO 4 - chromium). 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 series of acids, other suffixes are also used (HClO - chlorine ovatist aya, HClO 2 - chlorine ist aya, HClO 3 - chlorine ovate aya, HClO 4 - chlorine n and I).
FROM 
from the point of view of the theory of electrolytic dissociation, acids are electrolytes that dissociate in an aqueous solution with the formation of only hydrogen ions as cations:
N x A xN + + A x-
The presence of H + -ions is due to a change in the color of indicators in acid solutions: litmus (red), methyl orange (pink).
Preparation and properties of acids
a) obtaining acids.
1) Anoxic 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:
ВаВr 2 + H 2 SO 4 = ВаSO 4 + 2 HBr,
CuSO 4 + H 2 S \u003d H 2 SO 4 + CuS ,
FeS + H 2 SO 4 (razb.) \u003d H 2 S + FeSO 4,
NaCl (solid) + H 2 SO 4 (conc.) \u003d HCl + NaHSO 4,
AgNO 3 + HCl \u003d AgCl + HNO 3,
4) In some cases, redox reactions can be used to obtain acids:
3P + 5HNO 3 + 2H 2 O \u003d 3H 3 RO 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 \u003d Na 2 SiO 3 + 2H 2 O
2) The interaction of acids with basic and amphoteric oxides has been discussed above.
3) The interaction of acids with salts is an exchange reaction with the formation of salt and water. This reaction goes to completion if the reaction product is an insoluble or volatile substance, or a weak electrolyte.
Ni 2 SiO 3 + 2HCl \u003d 2NaCl + H 2 SiO 3
Na 2 CO 3 + H 2 SO 4 \u003d Na 2 SO 4 + H 2 O + CO 2
4) The interaction of acids with metals is a redox process. The reducing agent is a metal, the oxidizing agent is hydrogen ions (non-oxidizing acids: HCl, HBr, HI, H 2 SO 4 (dilute), H 3 PO 4) or an anion of the acid residue (oxidizing acids: H 2 SO 4 (conc), HNO 3(conc and dil)). The reaction products of the interaction of non-oxidizing acids with metals in the series of voltages up to hydrogen are salt and gaseous hydrogen:
Zn + H 2 SO 4 (razb) \u003d ZnSO 4 + H 2
Zn + 2HCl \u003d ZnCl 2 + H 2
Oxidizing acids interact with almost all metals, including low-activity ones (Cu, Hg, Ag), while acid anion reduction products, salt and water are formed:
Cu + 2H 2 SO 4 (conc.) \u003d CuSO 4 + SO 2 + 2 H 2 O,
Pb + 4HNO 3 (conc) \u003d 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 - as acids:
Cr (OH) 3 + NaOH \u003d Na (the reaction takes place in an alkali solution);
Cr (OH) 3 + NaOH \u003d NaCrO 2 + 2H 2 O (the reaction proceeds between solids 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 \u003d BeO + H 2 O.
SALT- ionic compounds consisting of metal cations (or ammonium) and anions of acid residues. Any salt can be considered as the product of the neutralization of a base with an acid. Depending on the ratio in which the acid and base are taken, salts are obtained: medium(ZnSO 4, MgCl 2) - the product of complete neutralization of the base with acid, sour(NaHCO 3, KH 2 PO 4) - with an excess of acid, main(CuOHCl, AlOHSO 4) - with an excess of base.
The names of salts according to international nomenclature are formed from two words: the names 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 brackets. 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 basic salts are formed by adding the word hydroxo- or dihydroxo-: (AlOH)Cl 2 - aluminum hydroxochloride, 2 SO 4 - chromium (III) dihydroxosulfate.
Preparation and properties of salts
a ) chemical properties of salts.
1) The interaction of salts with metals is a redox process. At the same time, the metal to the left in the electrochemical series of voltages displaces the following ones from solutions of their salts:
Zn + CuSO 4 \u003d ZnSO 4 + Cu
Alkali and alkaline earth metals are not used to restore other metals from aqueous solutions of their salts, since they interact with water, displacing hydrogen:
2Na + 2H 2 O \u003d H 2 + 2NaOH.
2) The interaction of salts with acids and alkalis was discussed above.
3) The interaction of salts with each other in a solution proceeds irreversibly only if one of the products is a poorly soluble substance:
BaCl 2 + Na 2 SO 4 \u003d 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) ways to get 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 \u003d CuCl 2,
2) Interaction of metals with salt solutions:
Fe + CuCl 2 \u003d FeCl 2 + Cu.
3) Interaction of metals with acids:
Fe + 2HCl \u003d FeCl 2 + H 2 .
4) Interaction of acids with bases and amphoteric hydroxides:
3HCl + Al(OH) 3 \u003d AlCl 3 + 3H 2 O.
5) Interaction of acids with basic and amphoteric oxides:
2HNO 3 + CuO \u003d Cu (NO 3) 2 + 2H 2 O.
6) Interaction of acids with salts:
HCl + AgNO 3 \u003d AgCl + HNO 3.
7) Interaction of alkalis with salts in solution:
3KOH + FeCl 3 \u003d Fe (OH) 3 + 3KCl.
8) The interaction of two salts in solution:
NaCl + AgNO 3 \u003d NaNO 3 + AgCl.
9) Interaction of alkalis with acidic and amphoteric oxides:
Ca (OH) 2 + CO 2 \u003d CaCO 3 + H 2 O.
10) Interaction of oxides of various nature with each other:
CaO + CO 2 \u003d CaCO 3.
Salts are found in nature in the form of minerals and rocks, in a dissolved state in the water of the oceans and seas.
Before discussing the chemical properties of bases and amphoteric hydroxides, let's clearly define what it is?
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 as Me(OH) 2 . However, there are exceptions. So, the hydroxides Zn (OH) 2, Be (OH) 2, Pb (OH) 2, Sn (OH) 2 do not belong to the bases.
2) Amphoteric hydroxides include metal hydroxides in the oxidation state +3, +4, and, as exceptions, hydroxides Zn (OH) 2, Be (OH) 2, Pb (OH) 2, Sn (OH) 2. Metal hydroxides in the oxidation state +4 are not found in the USE assignments, therefore they will not be considered.
Chemical properties of bases
All bases are divided into:
Recall 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 capable of entering into those reactions that insoluble bases do not enter into.
Reaction 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, 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 with a lack of acid, for example:
Interaction with acid oxides
Alkalis react with all acidic oxides to form salts and often water:
Insoluble bases are able to react 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 salts1:
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
With silicon dioxide, due to its exceptional inertness, only the strongest bases, alkalis, react. In this case, normal salts are formed. The reaction does not proceed 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, such a 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 the Na salt, the Na 3 salt is formed:
The interaction of bases with salts
Any base reacts with any salt only if two conditions are met simultaneously:
1) solubility of starting compounds;
2) the presence of a precipitate or gas among the reaction products
For example:
Thermal stability of bases
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. The highest decomposition temperature for calcium hydroxide is about 1000 o C:
Insoluble hydroxides have much more low temperatures decomposition. So, 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 +3 oxidation state, 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 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 +3 oxidation state, i.e. type Me (OH) 3, do not react with acid 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 to the corresponding oxide and water.
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 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 poorly soluble substance white color(slaked lime).
Getting the grounds
Getting the grounds and alkalis can be produced different 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 in the following way:
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
1. Bases interact with acids to form salt and water:
Cu(OH) 2 + 2HCl = CuCl 2 + 2H 2 O
2. With acid oxides, forming salt and water:
Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O
3. Alkalis react with amphoteric oxides and hydroxides, forming salt and water:
2NaOH + Cr 2 O 3 \u003d 2NaCrO 2 + H 2 O
KOH + Cr(OH) 3 = KCrO 2 + 2H 2 O
4. Alkalis interact with soluble salts, forming either a weak base, or a precipitate, or a gas:
2NaOH + NiCl 2 \u003d Ni (OH) 2 ¯ + 2NaCl
base
2KOH + (NH 4) 2 SO 4 \u003d 2NH 3 + 2H 2 O + K 2 SO 4
Ba(OH) 2 + Na 2 CO 3 = BaCO 3 ¯ + 2NaOH
5. Alkalis react with some metals, which correspond to amphoteric oxides:
2NaOH + 2Al + 6H 2 O = 2Na + 3H 2
6. The action of alkali on the indicator:
Oh - + phenolphthalein ® raspberry color
Oh - + litmus ® Blue colour
7. Decomposition of some bases when heated:
Сu(OH) 2 ® CuO + H 2 O
Amphoteric hydroxides- chemical compounds that exhibit the properties of both bases and acids. Amphoteric hydroxides correspond to amphoteric oxides (see section 3.1).
Amphoteric hydroxides are usually written in the form of a base, but they can also be represented as an acid:
Zn(OH) 2 Û H 2 ZnO 2
base to
Chemical properties amphoteric hydroxides
1. Amphoteric hydroxides interact with acids and acid oxides:
Be(OH) 2 + 2HCl = BeCl 2 + 2H 2 O
Be(OH) 2 + SO 3 = BeSO 4 + H 2 O
2. Interact with alkalis and basic oxides of alkali and alkaline earth metals:
Al(OH) 3 + NaOH = NaAlO 2 + 2H 2 O;
H 3 AlO 3 acid sodium metaaluminate
(H 3 AlO 3 ® HAlO 2 + H 2 O)
2Al(OH) 3 + Na 2 O = 2NaAlO 2 + 3H 2 O
All amphoteric hydroxides are weak electrolytes.
salt
salt- These are complex substances consisting of metal ions and an acid residue. Salts are products of complete or partial replacement of hydrogen ions by metal (or ammonium) ions in acids. Types of salts: medium (normal), acid and basic.
Medium salts- these are products of complete replacement of hydrogen cations in acids with metal (or ammonium) ions: Na 2 CO 3, NiSO 4, NH 4 Cl, etc.
Chemical properties of medium salts
1. Salts interact with acids, alkalis and other salts, forming either a weak electrolyte or a precipitate; or gas:
Ba(NO 3) 2 + H 2 SO 4 = BaSO 4 ¯ + 2HNO 3
Na 2 SO 4 + Ba(OH) 2 = BaSO 4 ¯ + 2NaOH
CaCl 2 + 2AgNO 3 \u003d 2AgCl¯ + Ca (NO 3) 2
2CH 3 COONa + H 2 SO 4 = Na 2 SO 4 + 2CH 3 COOH
NiSO 4 + 2KOH \u003d Ni (OH) 2 ¯ + K 2 SO 4
base
NH 4 NO 3 + NaOH \u003d NH 3 + H 2 O + NaNO 3
2. Salts interact with more active metals. A more active metal displaces a less active metal from a salt solution (Appendix 3).
Zn + CuSO 4 \u003d ZnSO 4 + Cu
Acid salts- these are products of incomplete replacement of hydrogen cations in acids with metal (or ammonium) ions: NaHCO 3, NaH 2 PO 4, Na 2 HPO 4, etc. Acid salts can only be formed by polybasic acids. Almost all acidic salts are highly soluble in water.
Obtaining acid salts and converting them into medium
1. Acid salts are obtained by reacting an excess of acid or acid oxide with a base:
H 2 CO 3 + NaOH = NaHCO 3 + H 2 O
CO 2 + NaOH = NaHCO 3
2. When an excess of acid interacts with a basic oxide:
2H 2 CO 3 + CaO \u003d Ca (HCO 3) 2 + H 2 O
3. Acid salts are obtained from medium salts by adding acid:
eponymous
Na 2 SO 3 + H 2 SO 3 \u003d 2NaHSO 3;
Na 2 SO 3 + HCl \u003d NaHSO 3 + NaCl
4. Acid salts are converted to medium using alkali:
NaHCO 3 + NaOH = Na 2 CO 3 + H 2 O
Basic salts are products of incomplete substitution of hydroxo groups (OH - ) bases with an acidic residue: MgOHCl, AlOHSO 4, etc. Basic salts can only be formed by weak bases of polyvalent metals. These salts are generally sparingly soluble.
Obtaining basic salts and converting them to medium
1. Basic salts are obtained by reacting an excess of a base with an acid or acid oxide:
Mg(OH) 2 + HCl = MgOHCl¯ + H 2 O
hydroxo-
magnesium chloride
Fe(OH) 3 + SO 3 = FeOHSO 4 ¯ + H 2 O
hydroxo-
iron(III) sulfate
2. Basic salts are formed from an average salt by adding a lack of alkali:
Fe 2 (SO 4) 3 + 2NaOH \u003d 2FeOHSO 4 + Na 2 SO 4
3. Basic salts are converted to medium ones by adding an acid (preferably the one that corresponds to the salt):
MgOHCl + HCl \u003d MgCl 2 + H 2 O
2MgOHCl + H 2 SO 4 \u003d MgCl 2 + MgSO 4 + 2H 2 O
ELECTROLYTES
electrolytes- these are substances that decompose into ions in solution under the influence of polar solvent molecules (H 2 O). According to the ability to dissociate (decay into ions), electrolytes are conditionally divided into strong and weak. Strong electrolytes dissociate almost completely (in dilute solutions), while weak ones decompose into ions only partially.
Strong electrolytes include:
strong acids (see p. 20);
strong bases - alkalis (see p. 22);
almost all soluble salts.
Weak electrolytes include:
Weak acids (see p. 20);
bases are not alkalis;
One of the main characteristics of a weak electrolyte is dissociation constant – To . For example, for a monobasic acid,
HA Û H + + A - ,
where, is the equilibrium concentration of H + ions;
is the equilibrium concentration of acid anions A - ;
is the equilibrium concentration of acid molecules,
Or for a weak foundation,
MOH Û M + +OH - ,
,
where, is the equilibrium concentration of cations M + ;
– equilibrium concentration of hydroxide ions OH - ;
is the equilibrium concentration of weak base molecules.
Dissociation constants of some weak electrolytes (at t = 25°С)
| Substance | To | Substance | To |
| HCOOH | K = 1.8×10 -4 | H3PO4 | K 1 \u003d 7.5 × 10 -3 |
| CH3COOH | K = 1.8×10 -5 | K 2 \u003d 6.3 × 10 -8 | |
| HCN | K = 7.9×10 -10 | K 3 \u003d 1.3 × 10 -12 | |
| H2CO3 | K 1 \u003d 4.4 × 10 -7 | HClO | K = 2.9×10 -8 |
| K 2 \u003d 4.8 × 10 -11 | H3BO3 | K 1 \u003d 5.8 × 10 -10 | |
| HF | K = 6.6×10 -4 | K 2 \u003d 1.8 × 10 -13 | |
| HNO 2 | K = 4.0×10 -4 | K 3 \u003d 1.6 × 10 -14 | |
| H2SO3 | K 1 \u003d 1.7 × 10 -2 | H2O | K = 1.8×10 -16 |
| K 2 \u003d 6.3 × 10 -8 | NH 3 × H 2 O | K = 1.8×10 -5 | |
| H 2 S | K 1 \u003d 1.1 × 10 -7 | Al(OH)3 | K 3 \u003d 1.4 × 10 -9 |
| K 2 \u003d 1.0 × 10 -14 | Zn(OH) 2 | K 1 \u003d 4.4 × 10 -5 | |
| H2SiO3 | K 1 \u003d 1.3 × 10 -10 | K 2 \u003d 1.5 × 10 -9 | |
| K 2 \u003d 1.6 × 10 -12 | Cd(OH)2 | K 2 \u003d 5.0 × 10 -3 | |
| Fe(OH)2 | K 2 \u003d 1.3 × 10 -4 | Cr(OH)3 | K 3 \u003d 1.0 × 10 -10 |
| Fe(OH)3 | K 2 \u003d 1.8 × 10 -11 | Ag(OH) | K = 1.1×10 -4 |
| K 3 \u003d 1.3 × 10 -12 | Pb(OH)2 | K 1 \u003d 9.6 × 10 -4 | |
| Cu(OH)2 | K 2 \u003d 3.4 × 10 -7 | K 2 \u003d 3.0 × 10 -8 | |
| Ni(OH)2 | K 2 \u003d 2.5 × 10 -5 |
3. Hydroxides
Hydroxides form an important group among multielement compounds. Some of them exhibit the properties of bases (basic hydroxides) - NaOH, Ba(OH ) 2, etc.; others exhibit the properties of acids (acid hydroxides) - HNO3, H3PO4 and others. There are also amphoteric hydroxides, which, depending on the conditions, can exhibit both the properties of bases and the properties of acids - Zn (OH) 2, Al (OH) 3, etc.
3.1. Classification, obtaining and properties of bases
Bases (basic hydroxides), from the standpoint of the theory of electrolytic dissociation, are substances that dissociate in solutions with the formation of OH hydroxide ions - .
According to modern nomenclature, they are usually called hydroxides of elements, indicating, if necessary, the valence of the element (Roman numerals in brackets): KOH - potassium hydroxide, sodium hydroxide NaOH , calcium hydroxide Ca(OH ) 2 , chromium hydroxide ( II)-Cr(OH ) 2 , chromium hydroxide ( III) - Cr (OH) 3.
Metal hydroxides usually divided into two groups: soluble in water(formed by alkali and alkaline earth metals - Li , Na , K , Cs , Rb , Fr , Ca , Sr , Ba and therefore called alkalis) and insoluble in water. The main difference between them is that the concentration of OH ions - in alkali solutions it is quite high, but for insoluble bases it is determined by the solubility of the substance and is usually very small. However, small equilibrium concentrations of the OH ion - even in solutions of insoluble bases determine the properties of this class of compounds.
According to the number of hydroxyl groups (acidity) , capable of being replaced by an acid residue, are distinguished:
Single acid bases KOH, NaOH
Diacid bases - Fe (OH) 2, Ba (OH) 2;
Triacid bases - Al (OH) 3, Fe (OH) 3.
Getting the grounds
1. A common method for obtaining bases is the exchange reaction, with which both insoluble and soluble bases can be obtained:
CuSO 4 + 2KOH \u003d Cu (OH) 2 ↓ + K 2 SO 4,
K 2 SO 4 + Ba(OH) 2 = 2KOH + BaCO 3↓ .
When soluble bases are obtained by this method, an insoluble salt precipitates.
When obtaining water-insoluble bases with amphoteric properties, an excess of alkali should be avoided, since dissolution of the amphoteric base may occur, for example,
AlCl 3 + 3KOH \u003d Al (OH) 3 + 3KCl,
Al (OH) 3 + KOH \u003d K.
In such cases, ammonium hydroxide is used to obtain hydroxides, in which amphoteric oxides do not dissolve:
AlCl 3 + 3NH 4 OH \u003d Al (OH) 3 ↓ + 3NH 4 Cl.
Silver and mercury hydroxides decompose so easily that when you try to obtain them by an exchange reaction, instead of hydroxides, oxides precipitate:
2AgNO 3 + 2KOH \u003d Ag 2 O ↓ + H 2 O + 2KNO 3.
2. Alkalis in technology are usually obtained by electrolysis of aqueous solutions of chlorides:
2NaCl + 2H 2 O \u003d 2NaOH + H 2 + Cl 2.
(total electrolysis reaction)
Alkalis can also be obtained by reacting alkali and alkaline earth metals or their oxides with water:
2 Li + 2 H 2 O \u003d 2 LiOH + H 2,
SrO + H 2 O \u003d Sr (OH) 2.
Chemical properties of bases
1. All water-insoluble bases decompose when heated to form oxides:
2 Fe (OH) 3 \u003d Fe 2 O 3 + 3 H 2 O,
Ca (OH) 2 \u003d CaO + H 2 O.
2. The most characteristic reaction of bases is their interaction with acids - the neutralization reaction. It includes both alkalis and insoluble bases:
NaOH + HNO 3 \u003d NaNO 3 + H 2 O,
Cu(OH) 2 + H 2 SO 4 = CuSO 4 + 2H 2 O.
3. Alkalis interact with acidic and amphoteric oxides:
2KOH + CO 2 \u003d K 2 CO 3 + H 2 O,
2NaOH + Al 2 O 3 \u003d 2NaAlO 2 + H 2 O.
4. Bases can react with acid salts:
2NaHSO 3 + 2KOH \u003d Na 2 SO 3 + K 2 SO 3 + 2H 2 O,
Ca(HCO 3) 2 + Ba(OH) 2 = BaCO 3↓ + CaCO 3 + 2H 2 O.
Cu (OH) 2 + 2NaHSO 4 \u003d CuSO 4 + Na 2 SO 4 + 2H 2 O.
5. It is necessary to especially emphasize the ability of alkali solutions to react with some non-metals (halogens, sulfur, white phosphorus, silicon):
2 NaOH + Cl 2 \u003d NaCl + NaOCl + H 2 O (in the cold),
6 KOH + 3 Cl 2 = 5 KCl + KClO 3 + 3 H 2 O (when heated)
6KOH + 3S = K 2 SO 3 + 2K 2 S + 3H 2 O,
3KOH + 4P + 3H 2 O \u003d PH 3 + 3KH 2 PO 2,
2NaOH + Si + H 2 O \u003d Na 2 SiO 3 + 2H 2.
6. In addition, concentrated solutions of alkalis, when heated, are also capable of dissolving some metals (those whose compounds have amphoteric properties):
2Al + 2NaOH + 6H 2 O = 2Na + 3H 2,
Zn + 2KOH + 2H 2 O \u003d K 2 + H 2.
Alkali solutions have a pH> 7 (alkaline), change the color of the indicators (litmus - blue, phenolphthalein - purple).
M.V. Andryukhova, L.N. Borodin