Getting and properties of bases. Reasons: classification and chemical properties
Bases are complex compounds with two main structural components:
- Hydroxo group (one or more). Hence, by the way, the second name of these substances - "hydroxides".
- Metal atom or ammonium ion (NH4 +).
The name of the bases 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 the formation of bases should be considered when the hydroxyl 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 the 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 the valency of the metals entering into the reaction. Examples in this case are the formulas of substances such 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 acting on a certain indicator with a solution. In this case, it will noticeably change its color: for example, it will turn from white to blue, and phenolphthalein - to raspberry.
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 hydroxyl group and the hydrogen ion, when combined, turn into water. This reaction is called a neutralization reaction because after it there is no alkali or acid left.
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 formation of a new salt and a new, most often insoluble, base as a result of the reaction.
Finally, the chemical properties of the bases perfectly manifest themselves during thermal action on them - heating. Here, when carrying out certain experiments, it should be borne in mind that practically all bases, with the exception of alkalis, behave extremely unstable when heated. The overwhelming majority of them decompose almost instantly into the corresponding oxide and water. And if we take the bases of metals such as silver and mercury, then under normal conditions they cannot be obtained, since they begin to decay already at room temperature.
a) obtaining grounds.
1) The general method for the preparation of bases is the 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 = 2KON + BaCO 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 = 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 - a 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 = СuSО 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 the end only when at least one of the obtained 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, the molecules of which 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 an acid residue. Hydrogen atoms in acids are capable of being replaced or exchanged for metal atoms, thus forming salts.
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 - ortho-arsenic.
Depending on the composition of the acid residue, acids are subdivided 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 linked through oxygen to the central atom: H - O - E. The names of anoxic acids are formed from the root of the Russian name for a non-metal, a connecting vowel - O- 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), which is part of the acid residue, is in the highest oxidation state, then suffixes are added to the root of the Russian name of the element -n-, -ev-, or - ov- and further ending -and I-(H 2 SO 4 - sulfuric, H 2 CrO 4 - chrome). If the oxidation state of the central atom is lower, then the suffix -ist-(H 2 SO 3 - sulphurous). If the non-metal forms a series of acids, use other suffixes (HClO - chlorine ovist ah, HClO 2 - chlorine ist ah, HClO 3 - chlorine ovate ah, HClO 4 - chlorine n and I).
WITH 
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:
H x A xH + + A x-
The presence of H + ions caused a change in the color of indicators in acid solutions: litmus (red), methyl orange (pink).
Obtaining and properties of acids
a) obtaining acids.
1) Anoxic acids can be obtained by direct combination of non-metals with hydrogen and subsequent dissolution of the corresponding gases in water:
2) Oxygen-containing acids can often be obtained by the interaction of acid oxides with water.
3) Both anoxic 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 (par.) = 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 obtain 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 goes to the end 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 a redox process. Reducing agent - metal, oxidizing agent - hydrogen ions (non-oxidizing acids: HCl, HBr, HI, H 2 SO 4 (diluted), H 3 PO 4) or anion of the acid residue (acid-oxidizing agents: H 2 SO 4 (conc.), HNO 3 (end and split)). The products of the reaction of the interaction of non-oxidizing acids with metals standing in a series of voltages up to hydrogen are salt and gaseous hydrogen:
Zn + H 2 SO 4 (diluted) = ZnSO 4 + H 2
Zn + 2HCl = ZnCl 2 + H 2
Oxidizing acids interact with almost all metals, including low-activity ones (Cu, Hg, Ag), thus forming the reduction products of the acid anion, salt and water:
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 show 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 = Na (the reaction proceeds in an alkali solution);
Cr (OH) 3 + NaOH = NaCrO 2 + 2H 2 O (the reaction takes place 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 = BeO + H 2 O.
SALTS- ionic compounds, consisting of metal cations (or ammonium) and anions of acid residues. Any salt can be considered as a product of a base neutralization reaction with an acid. Depending on the ratio of acid and base taken, 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 an excess of acid, the main(CuOHCl, AlOHSO 4) - with an excess of base.
The names of salts according to the international nomenclature are formed from two words: the names of the acid anion in the nominative case and the metal cation in the genitive, indicating its oxidation state, if it is a variable, in Roman numerals in brackets. For example: Cr 2 (SO 4) 3 - chromium (III) sulfate, AlCl 3 - aluminum chloride. The names of acidic salts are formed by the addition of 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 basic salts are formed by the addition of the word hydroxy or dihydroxo: (AlOH) Cl 2 - aluminum hydroxochloride, 2 SO 4 - chromium (III) dihydroxosulfate.
Obtaining and properties of salts
a ) chemical properties of salts.
1) The interaction of salts with metals is a redox process. In this case, the metal standing to the left in the electrochemical series of voltages displaces the following ones from solutions of their salts:
Zn + CuSO 4 = ZnSO 4 + Cu
Alkali and alkaline earth metals are not used 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 a solution is irreversible only if one of the products is a slightly soluble substance:
BaCl 2 + Na 2 SO 4 = BaSO 4 + 2NaCl.
4) Hydrolysis of salts - the exchange decomposition of some salts with water. Hydrolysis of salts will be discussed in detail in the topic "electrolytic dissociation".
b) methods of obtaining salts.
In laboratory practice, the following methods of 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 different nature with each other:
CaO + CO 2 = CaCO 3.
Salts occur naturally in the form of minerals and rocks, dissolved in the water of the oceans and seas.
Bases (hydroxides)- complex substances, the molecules of which contain one or more hydroxy OH groups. Most often, the bases are composed of a metal atom and an OH group. For example, NaOH is sodium hydroxide, Ca (OH) 2 is calcium hydroxide, etc.
There is a base - ammonium hydroxide, in which the hydroxy group is attached not to the metal, but to the NH 4 + ion (ammonium cation). Ammonium hydroxide is formed by dissolving ammonia in water (the reaction of adding water to ammonia):
NH 3 + H 2 O = NH 4 OH (ammonium hydroxide).
The valence of the gyroxy group is 1. The number of hydroxyl groups in the base molecule depends on the valence of the metal and is equal to it. For example, NaOH, LiOH, Al (OH) 3, Ca (OH) 2, Fe (OH) 3, etc.
All the reasons - solids that have different colors. Some bases are readily soluble in water (NaOH, KOH, etc.). However, most of them do not dissolve in water.
Bases that are soluble in water are called alkalis. Alkali solutions are "soapy", slippery to the touch and rather caustic. Alkalis include hydroxides of alkali and alkaline earth metals (KOH, LiOH, RbOH, NaOH, CsOH, Ca (OH) 2, Sr (OH) 2, Ba (OH) 2, etc.). The rest are insoluble.
Insoluble bases- these are amphoteric hydroxides, which, when interacting with acids, act as bases, and with alkali behave like acids.
Different bases differ in their ability to split off hydroxy groups, so they are divided into strong and weak bases.
Strong bases in aqueous solutions easily give up their hydroxy groups, while weak ones do not.
Chemical properties of bases
The chemical properties of bases are characterized by their ratio to acids, acid anhydrides and salts.
1. Affect indicators... Indicators change their color depending on interaction with different chemicals. In neutral solutions - they have one color, in acid solutions - another. When interacting with bases, they change their color: the methyl orange indicator turns yellow, the litmus indicator turns into blue color and phenolphthalein becomes fuchsia.
2. Interact with acidic oxides with the formation of salt and water:
2NaOH + SiO 2 → Na 2 SiO 3 + H 2 O.
3. Reacts with acids, forming salt and water. The reaction of interaction of a base with an acid is called a neutralization reaction, since after its completion the medium becomes neutral:
2KOH + H 2 SO 4 → K 2 SO 4 + 2H 2 O.
4. React with salts, forming new salt and base:
2NaOH + CuSO 4 → Cu (OH) 2 + Na 2 SO 4.
5. Able to decompose when heated into water and basic oxide:
Cu (OH) 2 = CuO + H 2 O.
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Metal and hydroxyl group (OH). For example, sodium hydroxide - NaOH, calcium hydroxide - Ca(OH) 2 , barium hydroxide - Ba(OH) 2, etc.
Getting hydroxides.
1. Exchange reaction:
CaSO 4 + 2NaOH = Ca (OH) 2 + Na 2 SO 4,
2. Electrolysis of aqueous solutions of salts:
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 dissolve in water (alkali) and are insoluble. For example, KOH- dissolves in water, and Ca(OH) 2 - slightly soluble, has a solution white... 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 = K 2 CO 3 + H 2 O.
5. Alkalis can react differently with some non-metals 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 + HNO 3 = KNO 3 + H 2 O.
Insoluble base: copper hydroxide
Foundations- electrolytes are called, in solutions of which there are no anions, except for hydroxide ions (anions are ions that have a negative charge, in this case, they are OH - ions). Names grounds consist 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 can be used, for example sodium hydroxide(NaOH) - sodium alkali.
Sodium hydroxide, sodium hydroxide, sodium alkali, caustic soda- all this is one and the same substance, the chemical formula of which is NaOH. Anhydrous sodium hydroxide is white crystalline substance... Solution - clear liquid, seemingly indistinguishable from water. Be careful when using! Caustic soda burns the skin!
The classification of bases is based on their ability to dissolve in water. Some properties of bases depend on solubility in water. So, foundations soluble in water are called lye... These include sodium hydroxides(NaOH), potassium hydroxide(KOH), lithium (LiOH), sometimes they add to their number and calcium hydroxide(Ca (OH) 2)), although in fact it is a poorly soluble white substance (slaked lime).
Getting the grounds
Getting the grounds and alkalis can be produced different ways... To receive 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. Receiving sodium hydroxide and potassium hydroxide associated with the use electric current... During the electrolysis of an aqueous solution of sodium chloride or potassium chloride, hydrogen is released at the cathode, and chlorine at the anode, while in the solution where electrolysis occurs, it 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 resistant to heat. Sodium hydroxide can be melted and the melt brought to a boil, while it will not decompose. Alkalis Reacts easily with acids to form salt and water. This reaction is also called the neutralization reaction.
KOH + HCl → KCl + H 2 O
Alkalis interact with acidic oxides, resulting in the formation of salt and water.
2NaOH + CO 2 → Na 2 CO 3 + H 2 O
Insoluble bases, unlike alkalis, thermally unstable 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 forms during the reaction dissolves in water.
Cu (OH) 2 + 2HCl → CuCl 2 + 2H 2 O
Dissolution of an alkali metal in water, changing the indicator color to bright red Alkali metals are metals that, when interacting with water, 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 as follows:
2Na + 2H 2 O → 2NaOH + H 2
All alkali metals behave in a similar way. If, before starting the reaction, add the indicator phenolphthalein to the water, and then lower a piece of sodium into the water, then the sodium will slide through the water, leaving behind a bright pink trail of the formed alkali (alkali stains phenolphthalein into pink color)
Iron hydroxide
Iron hydroxide is the basis. Iron, depending on its oxidation state, forms two different bases: iron hydroxide, where iron can have valences (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) - a white gelatinous substance (precipitate in solution), which has strong reducing properties. Besides, iron hydroxide(Ii) very unstable. If the solution iron hydroxide(II) add a little alkali, then a green precipitate will fall out, which quickly darkens and turns into a brown precipitate of iron (III).
Iron hydroxide(III) has amphoteric properties, but its acidic properties are much weaker. Receive iron hydroxide(Iii) it 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