Bases (hydroxides) – complex substances, whose molecules in their composition have one or more OH hydroxyl groups. Most often, bases consist 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 (reactions of addition of water to ammonia):

NH 3 + H 2 O = NH 4 OH (ammonium hydroxide).

The valency of the hydroxyl group is 1. Number hydroxyl groups in the base molecule depends on the valency of the metal and is equal to it. For example, NaOH, LiOH, Al (OH) 3, Ca (OH) 2, Fe (OH) 3, etc.

All grounds - solids who have various colors. Some bases are highly soluble in water (NaOH, KOH, etc.). However, most of them do not dissolve in water.

Water-soluble bases are called alkalis. Alkali solutions are "soapy", slippery to the touch and quite 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 behave like acids with alkali.

Different bases differ in their ability to split off hydroxy groups, so they are divided into strong and weak bases according to the feature.

Strong bases easily donate their hydroxyl groups in aqueous solutions, but weak bases do not.

Chemical properties of bases

The chemical properties of bases are characterized by their relationship to acids, acid anhydrides and salts.

1. Act on indicators. Indicators change their color depending on the 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 into yellow, litmus indicator - in blue color, and phenolphthalein becomes fuchsia.

2. React with acidic oxides formation of salt and water:

2NaOH + SiO 2 → Na 2 SiO 3 + H 2 O.

3. React with acids, forming salt and water. The reaction of the 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 a new salt and base:

2NaOH + CuSO 4 → Cu(OH) 2 + Na 2 SO 4.

5. Able to decompose into water and basic oxide when heated:

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

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Hydroxides alkali metals- under normal conditions, they are solid white crystalline substances, hygroscopic, soapy to the touch, very soluble in water (their dissolution is an exothermic process), fusible. Hydroxides of alkaline earth metals Ca (OH) 2, Sr (OH) 2, Ba (OH) 2) are white powdery substances, much less soluble in water compared to alkali metal hydroxides. Water-insoluble bases usually form as gel-like precipitates that decompose on storage. For example, Cu (OH) 2 is a blue gelatinous precipitate.

3.1.4 Chemical properties of bases.

The properties of bases are due to the presence of OH - ions. There are differences in the properties of alkalis and water-insoluble bases, but the common property is the reaction of interaction with acids. The chemical properties of the bases are presented in table 6.

Table 6 - Chemical properties of bases

alkalis	Insoluble bases
All bases react with acids ( neutralization reaction)
2NaOH + H 2 SO 4 \u003d Na 2 SO 4 + 2H 2 O	Cr(OH) 2 + 2HC1 = CrC1 2 + 2H 2 O
Bases react with acidic oxides with the formation of salt and water: 6KOH + P 2 O 5 \u003d 2K 3 RO 4 + 3H 2 O
Alkalis react with salt solutions if one of the reaction products precipitates out(i.e. if an insoluble compound forms): CuSO 4 + 2KOH \u003d Cu (OH) 2  + K 2 SO 4 Na 2 SO 4 + Ba(OH) 2 = 2NaOH + BaSO 4 	Water-insoluble bases and amphoteric hydroxides decompose when heated to the corresponding oxide and water: Mn (OH) 2  MnO + H 2 O Cu (OH) 2  CuO + H 2 O
Alkalis can be detected with an indicator. In an alkaline environment: litmus - blue, phenolphthalein - raspberry, methyl orange - yellow

3.1.5 Essential foundations.

NaOH- caustic soda, caustic soda. Fusible (t pl = 320 °C) white hygroscopic crystals, highly soluble in water. The solution is soapy to the touch and is a dangerous caustic liquid. NaOH is one of the most important products of the chemical industry. It is required in large quantities for the purification of petroleum products, it is widely used in soap, paper, textile and other industries, as well as for the production of artificial fiber.

KOH- caustic potash. White hygroscopic crystals, highly soluble in water. The solution is soapy to the touch and is a dangerous caustic liquid. The properties of KOH are similar to those of NaOH, but potassium hydroxide is used much less frequently due to its higher cost.

Ca(OH) 2 - slaked lime. White crystals, slightly soluble in water. The solution is called “lime water”, the suspension is called “milk of lime”. Lime water is used to recognize carbon dioxide, it becomes cloudy when CO 2 is passed through. Hydrated lime is widely used in the construction industry as a basis for the manufacture of binders.

2. GROUNDS

Foundations – these are complex substances consisting of metal atoms and one or more hydroxo groups (OH -).

In terms of theory electrolytic dissociation these are electrolytes (substances whose solutions or melts conduct electric current), dissociating in aqueous solutions into metal cations and anions of only hydroxide - OH - ions.

Water-soluble bases are called alkalis. These include bases that are formed by metals of the 1st group of the main subgroup (LiOH, NaOHand others) and alkaline earth metals (C a(OH) 2,Sr(OH) 2, Va (OH) 2). Bases formed by metals of other groups periodic system practically insoluble in water. Alkalis in water dissociate completely:

NaOH® Na + + OH - .

PolyacidBases in water dissociate in steps:

Ba( OH) 2 ® BaOH + + OH - ,

Ba( OH) + Ba 2+ + OH -.

C bluntthe dissociation of bases explains the formation of basic salts.

Base nomenclature.

The bases are called as follows: first the word "hydroxide" is pronounced, and then the metal that forms it. If the metal has a variable valence, then it is indicated in the name.

KOH, potassium hydroxide;

Ca( Oh ) 2 – calcium hydroxide;

Fe( Oh ) 2 – iron hydroxide ( II);

Fe( Oh ) 3 – iron hydroxide ( III);

When compiling base formulas assuming that the molecule electrically neutral. The hydroxide ion always has a charge (-1). In a base molecule, their number is determined by the positive charge of the metal cation. The hydrocogroup is enclosed in parentheses, and the charge-equalizing index is placed at the bottom right behind the brackets:

Ca +2 (OH) - 2, Fe 3 +( OH) 3 - .

on the following grounds:

1. By acidity (according to the number of OH groups - in the base molecule): monoacid -NaOH, KOH , polyacid - Ca (OH) 2, Al (OH) 3.

2. By solubility: soluble (alkali) -LiOH, KOH , insoluble - Cu (OH) 2, Al (OH) 3.

3. By strength (according to the degree of dissociation):

a) strong α = 100%) - all soluble basesNaOH, LiOH, Ba(OH ) 2 , sparingly soluble Ca(OH)2.

b) weak ( α < 100 %) – все нерастворимые основания Cu (OH) 2, Fe (OH) 3 and soluble NH 4 OH.

4. By chemical properties: basic - C a(OH) 2, Na IS HE; amphoteric - Zn (OH) 2, Al (OH) 3.

Foundations

These are hydroxides of alkali and alkaline earth metals (and magnesium), as well as metals in minimum degree oxidation (if it has a variable value).

For example: NaOH, LiOH, mg ( OH) 2, Ca (OH) 2, Cr (OH) 2, Mn(OH) 2 .

Receipt

1. Interaction active metal with water:

2Na + 2H 2 O → 2NaOH + H 2

Ca + 2H 2 O → Ca(OH) 2 + H 2

Mg + 2 H 2 O mg ( Oh) 2 + H 2

2. Interaction basic oxides with water (only for alkali and alkaline earth metals):

Na 2 O + H 2 O → 2NaOH,

CaO+ H 2 O → Ca(OH)2.

3. An industrial method for obtaining alkalis is the electrolysis of salt solutions:

2NaCI + 4H 2 O 2NaOH + 2H 2 + CI 2

4. The interaction of soluble salts with alkalis, and for insoluble bases this the only way receipt:

Na 2 SO 4 + Ba(OH) 2 → 2NaOH + BaSO 4

MgSO 4 + 2NaOH → Mg (OH) 2 + Na 2 SO 4.

Physical properties

All bases are solids. Insoluble in water, except for alkalis. Alkalis are white crystalline substances, soapy to the touch, causing severe burns upon contact with the skin. That is why they are called "caustic". When working with alkalis, it is necessary to follow certain rules and use personal protective equipment (glasses, rubber gloves, tweezers, etc.).

If alkali gets on the skin, wash this place large quantity water until the soapiness disappears, and then neutralize with a solution of boric acid.

Chemical properties

The chemical properties of bases from the point of view of the theory of electrolytic dissociation are due to the presence in their solutions of an excess of free hydroxides -

OH ions - .

1. Changing the color of the indicators:

phenolphthalein - raspberry

litmus - blue

methyl orange - yellow

2. Interaction with acids to form salt and water (neutralization reaction):

2NaOH + H 2 SO 4 → Na 2 SO 4 + 2H 2 O,

Soluble

Cu(OH) 2 + 2HCI → CuCI 2 + 2H 2 O.

Insoluble

3. Interaction with acid oxides:

2 NaOH+ SO 3 → Na 2 SO 4 + H 2 O

4. Interaction with amphoteric oxides and hydroxides:

a) when melting:

2 NaOH+ AI 2 O 3 2 NaAIO 2 + H 2 O,

NaOH + AI(OH) 3 NaAIO 2 + 2H 2 O.

b) in solution:

2NaOH + AI 2 O 3 +3H 2 O → 2Na[ AI(OH) 4 ],

NaOH + AI(OH) 3 → Na.

5. Interaction with some simple substances(amphoteric metals, silicon and others):

2NaOH + Zn + 2H 2 O → Na 2 [Zn(OH) 4] + H 2

2NaOH+ Si + H 2 O → Na 2 SiO 3 + 2H 2

6. Interaction with soluble salts with the formation of precipitation:

2NaOH + CuSO 4 → Cu (OH) 2 + Na 2 SO 4,

Ba( OH) 2 + K 2 SO 4 → BaSO 4 + 2KOH.

7. Slightly soluble and insoluble bases decompose when heated:

Ca( oh)2 CaO + H 2 O,

Cu( oh)2 CuO + H2O.

blue color black color

Amphoteric hydroxides

These are metal hydroxides ( Be (OH) 2, AI (OH) 3, Zn (OH ) 2) and metals in an intermediate oxidation state (Cr(OH) 3, Mn(OH) 4).

Receipt

Amphoteric hydroxides are obtained by the interaction of soluble salts with alkalis taken in a deficiency or an equivalent amount, because. in excess they dissolve:

AICI 3 + 3NaOH → AI(OH) 3 +3NaCI.

Physical properties

These are solids, practically insoluble in water.Zn( OH) 2 - white, Fe (OH) 3 - brown color.

Chemical properties

Amphoteric Hydroxides exhibit the properties of bases and acids, and therefore interact with both acids and bases.

1. Interaction with acids to form salt and water:

Zn(OH) 2 + H 2 SO 4 → ZnSO 4 + 2H 2 O.

2. Interaction with solutions and melts of alkalis with the formation of salt and water:

AI( OH)3+ NaOHNa,

Fe 2 (SO 4) 3 + 3H 2 O,

2Fe(OH) 3 + Na 2 O 2NaFeO 2 + 3H 2 O.

Lab #2

Preparation and chemical properties of bases

Objective: acquainted with chemical properties grounds and ways to obtain them.

Glassware and reagents: test tubes, spirit lamp. A set of indicators, magnesium tape, solutions of salts of aluminum, iron, copper, magnesium; alkali( NaOH, KOH), distilled water.

Experience number 1. The interaction of metals with water.

Pour 3–5 cm3 of water into a test tube and dip a few pieces of finely chopped magnesium tape into it. Heat on an alcohol lamp for 3-5 minutes, cool and add 1-2 drops of phenolphthalein solution there. How did the color of the indicator change? Compare with point 1 on p. 27. Write the reaction equation. What metals interact with water?

Experience number 2. Preparation and properties of insoluble

grounds

In test tubes with dilute salt solutions MgCI 2, FeCI 3 , CuSO 4 (5–6 drops) add 6–8 drops of a dilute alkali solution NaOH before the formation of precipitation. Note their coloration. Write the reaction equations.

Divide the resulting blue precipitate Cu (OH) 2 into two test tubes. Add 2-3 drops of a dilute acid solution to one of them, the same amount of alkali to the other. In which test tube was the dissolution of the precipitate observed? Write the reaction equation.

Repeat this experiment with two other hydroxides obtained by exchange reactions. Note the observed phenomena, write down the reaction equations. Make a general conclusion about the ability of bases to interact with acids and alkalis.

Experience No. 3. Preparation and properties of amphoteric hydroxides

Repeat the previous experiment with aluminum salt solution ( AICI 3 or AI 2 (SO 4 ) 3). Observe the formation of a white cheesy precipitate of aluminum hydroxide and its dissolution upon the addition of both acid and alkali. Write the reaction equations. Why does aluminum hydroxide have the properties of both an acid and a base? What other amphoteric hydroxides do you know?

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 negative charge, in this case are OH ions. Titles grounds consist of three parts: the words hydroxide , to which the name of the metal is added (in 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- it's all the same stuff chemical formula which NaOH. Anhydrous sodium hydroxide- it's 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. To receive alkalis can be used chemical interaction 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 these methods have not been found in industry. practical value, of course, in addition to obtaining calcium hydroxide Ca(OH) 2 . Receipt sodium hydroxide and potassium hydroxide associated with the use electric current. With electrolysis aqueous solution sodium 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 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) - sodium hydroxide 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, 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 resulting alkali (alkali stains phenolphthalein in pink color)

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 restorative 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 acid properties it is much less pronounced. Get iron hydroxide(III) possible as a result chemical reaction exchange between iron salt and alkali. for example

Fe 2 (SO 4) 3 + 6 NaOH → 3 Na 2 SO 4 +2 Fe (OH) 3