Bases (hydroxides)– complex substances whose molecules contain one or more hydroxy OH 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 when ammonia is dissolved in water (the reaction of adding water to ammonia):
NH 3 + H 2 O = NH 4 OH (ammonium hydroxide).
The valency of the hydroxy 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 reasons - solids that have different colors. Some bases are highly soluble in water (NaOH, KOH, etc.). However, most of them are not soluble in water.
Bases soluble in water are called alkalis. Alkali solutions are “soapy”, slippery to the touch and quite caustic. Alkalies 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 act as bases when interacting with acids, and behave like acids with alkali.
Different bases have different abilities to remove hydroxy groups, so they are divided into strong and weak bases.
Strong bases in aqueous solutions easily give up their hydroxy groups, 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 color depending on interaction with different chemicals. In neutral solutions they have one color, in acid solutions they have another color. When interacting with bases, they change their color: the methyl orange indicator turns yellow, the litmus indicator turns blue, and phenolphthalein becomes fuchsia.
2. Interact with acid oxides with 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 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. Reacts with salts forming a new salt and base:
2NaOH + CuSO 4 → Cu(OH) 2 + Na 2 SO 4.
5. When heated, they can decompose into water and the main oxide:
Cu(OH) 2 = CuO + H 2 O.
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3. Hydroxides
Among multielement compounds, an important group is hydroxides. 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 that, depending on conditions, can exhibit both the properties of bases and the properties of acids - Zn (OH) 2, Al (OH) 3, etc.
3.1. Classification, preparation and properties of bases
From the standpoint of the theory of electrolytic dissociation, bases (basic hydroxides) are substances that dissociate in solutions to form OH hydroxide ions - .
According to modern nomenclature, they are usually called hydroxides of elements, indicating, if necessary, the valence of the element (in 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: water soluble(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 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, the properties of this class of compounds are determined.
By the number of hydroxyl groups (acidity) , capable of being replaced by an acidic residue, are distinguished:
Mono-acid bases - KOH, NaOH;
Diacid bases - Fe (OH) 2, Ba (OH) 2;
Triacid bases - Al (OH) 3, Fe (OH) 3.
Getting 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 + 2KOH = 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 preparing water-insoluble bases with amphoteric properties, excess alkali should be avoided, since dissolution of the amphoteric base may occur, for example,
AlCl 3 + 3KOH = Al(OH) 3 + 3KCl,
Al(OH) 3 + KOH = K.
In such cases, ammonium hydroxide is used to obtain hydroxides, in which amphoteric oxides do not dissolve:
AlCl 3 + 3NH 4 OH = Al(OH) 3 ↓ + 3NH 4 Cl.
Silver and mercury hydroxides decompose so easily that when trying to obtain them by exchange reaction, instead of hydroxides, oxides precipitate:
2AgNO 3 + 2KOH = 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 = 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 = 2 LiOH + H 2,
SrO + H 2 O = Sr (OH) 2.
Chemical properties of bases
1. All bases insoluble in water decompose when heated to form oxides:
2 Fe (OH) 3 = Fe 2 O 3 + 3 H 2 O,
Ca (OH) 2 = CaO + H 2 O.
2. 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 + 2H 2 O.
3. Alkalis interact with acidic and amphoteric oxides:
2KOH + CO 2 = K 2 CO 3 + H 2 O,
2NaOH + Al 2 O 3 = 2NaAlO 2 + H 2 O.
4. Bases can react with acidic salts:
2NaHSO 3 + 2KOH = 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 = 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 = 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 = PH 3 + 3KH 2 PO 2,
2NaOH + Si + H 2 O = 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 = K 2 + H 2.
Alkaline solutions have a pH> 7 (alkaline environment), change the color of indicators (litmus - blue, phenolphthalein - purple).
M.V. Andryukhova, L.N. Borodina
Grounds – complex substances that consist of a metal cation Me + (or a metal-like cation, for example, ammonium ion NH 4 +) and a hydroxide anion OH -.
Based on their solubility in water, bases are divided into soluble (alkalis) And insoluble bases . There is also unstable foundations, which spontaneously decompose.
Getting grounds
1. Interaction of basic oxides with water. In this case, only those oxides that correspond to a soluble base (alkali). Those. in this way you can only get alkalis:
basic oxide + water = base
For example , sodium oxide forms in water sodium hydroxide(sodium hydroxide):
Na 2 O + H 2 O → 2NaOH
At the same time about copper(II) oxide With water does not react:
CuO + H 2 O ≠
2. Interaction of metals with water. Wherein react with waterunder normal conditionsonly alkali metals(lithium, sodium, potassium, rubidium, cesium), calcium, strontium and barium.In this case, a redox reaction occurs, hydrogen is the oxidizing agent, and the metal is the reducing agent.
metal + water = alkali + hydrogen
For example, potassium reacts with water very stormy:
2K 0 + 2H 2 + O → 2K + OH + H 2 0
3. Electrolysis of solutions of some alkali metal salts. As a rule, to obtain alkalis, electrolysis is carried out solutions of salts formed by alkali or alkaline earth metals and oxygen-free acids (except for hydrofluoric acid) - chlorides, bromides, sulfides, etc. This issue is discussed in more detail in the article .
For example , electrolysis of sodium chloride:
2NaCl + 2H 2 O → 2NaOH + H 2 + Cl 2
4. Bases are formed by the interaction of other alkalis with salts. In this case, only soluble substances interact, and an insoluble salt or an insoluble base should be formed in the products:
or
alkali + salt 1 = salt 2 ↓ + alkali
For example: Potassium carbonate reacts in solution with calcium hydroxide:
K 2 CO 3 + Ca(OH) 2 → CaCO 3 ↓ + 2KOH
For example: Copper(II) chloride reacts in solution with sodium hydroxide. In this case it falls out blue copper(II) hydroxide precipitate:
CuCl 2 + 2NaOH → Cu(OH) 2 ↓ + 2NaCl
Chemical properties of insoluble bases
1. Insoluble bases react with strong acids and their oxides (and some medium acids). In this case, salt and water.
insoluble base + acid = salt + water
insoluble base + acid oxide = salt + water
For example ,Copper(II) hydroxide reacts with strong hydrochloric acid:
Cu(OH) 2 + 2HCl = CuCl 2 + 2H 2 O
In this case, copper (II) hydroxide does not interact with the acid oxide weak carbonic acid - carbon dioxide:
Cu(OH) 2 + CO 2 ≠
2. Insoluble bases decompose when heated into oxide and water.
For example, Iron(III) hydroxide decomposes into iron(III) oxide and water when heated:
2Fe(OH) 3 = Fe 2 O 3 + 3H 2 O
3. Insoluble bases do not reactwith amphoteric oxides and hydroxides.
insoluble base + amphoteric oxide ≠
insoluble base + amphoteric hydroxide ≠
4. Some insoluble bases can act asreducing agents. Reducing agents are bases formed by metals with minimum or intermediate oxidation state, which can increase their oxidation state (iron (II) hydroxide, chromium (II) hydroxide, etc.).
For example , Iron (II) hydroxide can be oxidized with atmospheric oxygen in the presence of water to iron (III) hydroxide:
4Fe +2 (OH) 2 + O 2 0 + 2H 2 O → 4Fe +3 (O -2 H) 3
Chemical properties of alkalis
1. Alkalis react with any acids - both strong and weak . In this case, medium salt and water are formed. These reactions are called neutralization reactions. Education is also possible sour salt, if the acid is polybasic, at a certain ratio of reagents, or in excess acid. IN excess alkali medium salt and water are formed:
alkali (excess) + acid = medium salt + water
alkali + polybasic acid (excess) = acid salt + water
For example , Sodium hydroxide, when interacting with tribasic phosphoric acid, can form 3 types of salts: dihydrogen phosphates, phosphates or hydrophosphates.
In this case, dihydrogen phosphates are formed in an excess of acid, or when the molar ratio (ratio of the amounts of substances) of the reagents is 1:1.
NaOH + H 3 PO 4 → NaH 2 PO 4 + H 2 O
When the molar ratio of alkali and acid is 2:1, hydrophosphates are formed:
2NaOH + H3PO4 → Na2HPO4 + 2H2O
In an excess of alkali, or with a molar ratio of alkali to acid of 3:1, alkali metal phosphate is formed.
3NaOH + H3PO4 → Na3PO4 + 3H2O
2. Alkalis react withamphoteric oxides and hydroxides. Wherein ordinary salts are formed in the melt , A in solution - complex salts .
alkali (melt) + amphoteric oxide = medium salt + water
alkali (melt) + amphoteric hydroxide = medium salt + water
alkali (solution) + amphoteric oxide = complex salt
alkali (solution) + amphoteric hydroxide = complex salt
For example , when aluminum hydroxide reacts with sodium hydroxide in the melt sodium aluminate is formed. A more acidic hydroxide forms an acidic residue:
NaOH + Al(OH) 3 = NaAlO 2 + 2H 2 O
A in solution a complex salt is formed:
NaOH + Al(OH) 3 = Na
Please note how the complex salt formula is composed:first we select the central atom (toAs a rule, it is an amphoteric hydroxide metal).Then we add to it ligands- in our case these are hydroxide ions. The number of ligands is usually 2 times greater than the oxidation state of the central atom. But the aluminum complex is an exception; its number of ligands is most often 4. We enclose the resulting fragment in square brackets - this is a complex ion. We determine its charge and add the required number of cations or anions on the outside.
3. Alkalis interact with acidic oxides. At the same time, education is possible sour or medium salt, depending on the molar ratio of alkali and acid oxide. In an excess of alkali, a medium salt is formed, and in an excess of an acidic oxide, an acid salt is formed:
alkali (excess) + acid oxide = medium salt + water
or:
alkali + acid oxide (excess) = acid salt
For example , when interacting excess sodium hydroxide With carbon dioxide, sodium carbonate and water are formed:
2NaOH + CO 2 = Na 2 CO 3 + H 2 O
And when interacting excess carbon dioxide with sodium hydroxide only sodium bicarbonate is formed:
2NaOH + CO 2 = NaHCO 3
4. Alkalis interact with salts. Alkalis react only with soluble salts in solution, provided that Gas or sediment forms in the food . Such reactions proceed according to the mechanism ion exchange.
alkali + soluble salt = salt + corresponding hydroxide
Alkalies interact with solutions of metal salts, which correspond to insoluble or unstable hydroxides.
For example, sodium hydroxide reacts with copper sulfate in solution:
Cu 2+ SO 4 2- + 2Na + OH - = Cu 2+ (OH) 2 - ↓ + Na 2 + SO 4 2-
Also alkalis react with solutions of ammonium salts.
For example , Potassium hydroxide reacts with ammonium nitrate solution:
NH 4 + NO 3 - + K + OH - = K + NO 3 - + NH 3 + H 2 O
! When salts of amphoteric metals interact with excess alkali, a complex salt is formed!
Let's look at this issue in more detail. If the salt formed by the metal to which it corresponds amphoteric hydroxide , interacts with a small amount of alkali, then the usual exchange reaction occurs, and a precipitate occurshydroxide of this metal .
For example , excess zinc sulfate reacts in solution with potassium hydroxide:
ZnSO 4 + 2KOH = Zn(OH) 2 ↓ + K 2 SO 4
However, in this reaction it is not a base that is formed, but mphoteric hydroxide. And, as we already indicated above, amphoteric hydroxides dissolve in excess alkalis to form complex salts . T Thus, when zinc sulfate reacts with excess alkali solution a complex salt is formed, no precipitate forms:
ZnSO 4 + 4KOH = K 2 + K 2 SO 4
Thus, we obtain 2 schemes for the interaction of metal salts, which correspond to amphoteric hydroxides, with alkalis:
amphoteric metal salt (excess) + alkali = amphoteric hydroxide↓ + salt
amph.metal salt + alkali (excess) = complex salt + salt
5. Alkalis interact with acidic salts.In this case, medium salts or less acidic salts are formed.
sour salt + alkali = medium salt + water
For example , Potassium hydrosulfite reacts with potassium hydroxide to form potassium sulfite and water:
KHSO 3 + KOH = K 2 SO 3 + H 2 O
It is very convenient to determine the properties of acidic salts by mentally breaking the acidic salt into 2 substances - acid and salt. For example, we break sodium bicarbonate NaHCO 3 into uolic acid H 2 CO 3 and sodium carbonate Na 2 CO 3. The properties of bicarbonate are largely determined by the properties of carbonic acid and the properties of sodium carbonate.
6. Alkalis interact with metals in solution and melt. In this case, an oxidation-reduction reaction occurs, forming in the solution complex salt And hydrogen, in the melt - medium salt And hydrogen.
Note! Only those metals whose oxide with the minimum positive oxidation state of the metal is amphoteric react with alkalis in solution!
For example , iron does not react with alkali solution, iron (II) oxide is basic. A aluminum dissolves in aqueous alkali solution, aluminum oxide is amphoteric:
2Al + 2NaOH + 6H 2 + O = 2Na + 3H 2 0
7. Alkalies interact with non-metals. In this case, redox reactions occur. Usually, nonmetals are disproportionate in alkalis. They don't react with alkalis oxygen, hydrogen, nitrogen, carbon and inert gases (helium, neon, argon, etc.):
NaOH +O 2 ≠
NaOH +N 2 ≠
NaOH +C ≠
Sulfur, chlorine, bromine, iodine, phosphorus and other non-metals disproportionate in alkalis (i.e. they self-oxidize and self-recover).
For example, chlorinewhen interacting with cold lye goes into oxidation states -1 and +1:
2NaOH +Cl 2 0 = NaCl - + NaOCl + + H 2 O
Chlorine when interacting with hot lye goes into oxidation states -1 and +5:
6NaOH +Cl 2 0 = 5NaCl - + NaCl +5 O 3 + 3H 2 O
Silicon oxidized by alkalis to oxidation state +4.
For example, in solution:
2NaOH + Si 0 + H 2 + O= NaCl - + Na 2 Si +4 O 3 + 2H 2 0
Fluorine oxidizes alkalis:
2F 2 0 + 4NaO -2 H = O 2 0 + 4NaF - + 2H 2 O
You can read more about these reactions in the article.
8. Alkalis do not decompose when heated.
The exception is lithium hydroxide:
2LiOH = Li 2 O + H 2 O
The general properties of bases are determined by the presence of the OH - ion in their solutions, which creates an alkaline environment in the solution (phenolphthalein turns crimson, methyl orange turns yellow, litmus turns blue).
1. Chemical properties of alkalis:
1) interaction with acid oxides:
2KOH+CO 2 ®K 2 CO 3 +H 2 O;
2) reaction with acids (neutralization reaction):
2NaOH+ H 2 SO 4 ®Na 2 SO 4 +2H 2 O;
3) interaction with soluble salts (only if, when an alkali acts on a soluble salt, a precipitate forms or a gas is released):
2NaOH+ CuSO 4 ®Cu(OH) 2 ¯+Na 2 SO 4,
Ba(OH) 2 +Na 2 SO 4 ®BaSO 4 ¯+2NaOH, KOH(conc.)+NH 4 Cl(crystalline) ®NH 3 +KCl+H 2 O.
2. Chemical properties of insoluble bases:
1) interaction of bases with acids:
Fe(OH) 2 +H 2 SO 4 ®FeSO 4 +2H 2 O;
2) decomposition when heated. When heated, insoluble bases decompose into the basic oxide and water:
Cu(OH) 2 ®CuO+H 2 O
End of work -
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Atomic molecular studies in chemistry. Atom. Molecule. Chemical element. Mol. Simple complex substances. Examples
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All topics in this section:
Getting grounds
1. Preparation of alkalis: 1) interaction of alkali or alkaline earth metals or their oxides with water: Ca+2H2O®Ca(OH)2+H
Nomenclature of acids
The names of acids are derived from the element from which the acid is formed. At the same time, the names of oxygen-free acids usually have the ending -hydrogen: HCl - hydrochloric, HBr - hydrobromo
Chemical properties of acids
The general properties of acids in aqueous solutions are determined by the presence of H+ ions formed during the dissociation of acid molecules, thus, acids are proton donors: HxAn«xH+
Obtaining acids
1) interaction of acid oxides with water: SO3+H2O®H2SO4, P2O5+3H2O®2H3PO4;
Chemical properties of acid salts
1) acid salts contain hydrogen atoms that can take part in the neutralization reaction, so they can react with alkalis, turning into medium or other acid salts - with a smaller number
Obtaining acid salts
The acid salt can be obtained: 1) by the reaction of incomplete neutralization of a polybasic acid with a base: 2H2SO4+Cu(OH)2®Cu(HSO4)2+2H
Basic salts.
Basic (hydroxo salts) are salts that are formed as a result of incomplete replacement of the hydroxide ions of the base with acid anions. Single acid bases, e.g. NaOH, KOH,
Chemical properties of basic salts
1) basic salts contain hydroxo groups that can take part in the neutralization reaction, so they can react with acids, turning into intermediate salts or basic salts with less
Preparation of basic salts
The main salt can be obtained: 1) by the reaction of incomplete neutralization of the base with an acid: 2Cu(OH)2+H2SO4®(CuOH)2SO4+2H2
Medium salts.
Medium salts are the products of complete replacement of H+ ions of an acid with metal ions; they can also be considered as products of complete replacement of the OH ions of the base anion
Nomenclature of medium salts
In Russian nomenclature (used in technological practice) there is the following order of naming medium salts: the word is added to the root of the name of an oxygen-containing acid
Chemical properties of medium salts
1) Almost all salts are ionic compounds, therefore, in a melt and in an aqueous solution, they dissociate into ions (when current is passed through solutions or molten salts, the process of electrolysis occurs).
Preparation of medium salts
Most of the methods for obtaining salts are based on the interaction of substances of opposite nature - metals with non-metals, acidic oxides with basic ones, bases with acids (see Table 2).
The structure of the atom.
An atom is an electrically neutral particle consisting of a positively charged nucleus and negatively charged electrons. The atomic number of an element in the Periodic Table of Elements is equal to the charge of the nucleus
Composition of atomic nuclei
The nucleus consists of protons and neutrons. The number of protons is equal to the atomic number of the element. The number of neutrons in the nucleus is equal to the difference between the mass number of the isotope and
Electron
Electrons rotate around the nucleus in certain stationary orbits. Moving along its orbit, an electron does not emit or absorb electromagnetic energy. Emission or absorption of energy occurs
Rule for filling electronic levels and sublevels of elements
The number of electrons that can be at one energy level is determined by the formula 2n2, where n is the number of the level. Maximum filling of the first four energy levels: for the first
Ionization energy, electron affinity, electronegativity.
Ionization energy of an atom. The energy required to remove an electron from an unexcited atom is called the first ionization energy (potential) I: E + I = E+ + e- Ionization energy
Covalent bond
In most cases, when a bond is formed, the electrons of the bonded atoms are shared. This type of chemical bond is called a covalent bond (the prefix "co-" in Latin
Sigma and pi connections.
Sigma (σ)-, pi (π)-bonds - an approximate description of the types of covalent bonds in molecules of various compounds, the σ-bond is characterized by the fact that the density of the electron cloud is maximum
Formation of a covalent bond by a donor-acceptor mechanism.
In addition to the homogeneous mechanism of covalent bond formation outlined in the previous section, there is a heterogeneous mechanism - the interaction of oppositely charged ions - the H+ proton and
Chemical bonding and molecular geometry. BI3, PI3
Figure 3.1 Addition of dipole elements in NH3 and NF3 molecules
Polar and non-polar bond
A covalent bond is formed as a result of the sharing of electrons (to form common electron pairs), which occurs during the overlap of electron clouds. In education
Ionic bond
An ionic bond is a chemical bond that occurs through the electrostatic interaction of oppositely charged ions. Thus, the process of education and
Oxidation state
Valency 1. Valency is the ability of atoms of chemical elements to form a certain number of chemical bonds. 2. Valency values vary from I to VII (rarely VIII). Valens
Hydrogen bond
In addition to various heteropolar and homeopolar bonds, there is another special type of bond that has attracted increasing attention from chemists over the past two decades. This is the so-called hydrogen
Crystal lattices
So, the crystal structure is characterized by the correct (regular) arrangement of particles in strictly defined places in the crystal. When you mentally connect these points with lines, you get spaces.
Solutions
If crystals of table salt, sugar or potassium permanganate (potassium permanganate) are placed in a vessel with water, then we can observe how the amount of solid substance gradually decreases. At the same time, water
Electrolytic dissociation
Solutions of all substances can be divided into two groups: electrolytes conduct electric current, non-electrolytes do not conduct electricity. This division is conditional, because everything
Dissociation mechanism.
Water molecules are dipole, i.e. one end of the molecule is negatively charged, the other is positively charged. The molecule has a negative pole approaching the sodium ion, and a positive pole approaching the chlorine ion; surround io
Ionic product of water
Hydrogen index (pH) is a value characterizing the activity or concentration of hydrogen ions in solutions. The hydrogen indicator is designated pH. The hydrogen index is numerically
Chemical reaction
A chemical reaction is the transformation of one substance into another. However, such a definition needs one significant addition. In a nuclear reactor or accelerator, some substances are also converted
Methods for arranging coefficients in OVR
Electronic balance method 1). We write the equation of the chemical reaction KI + KMnO4 → I2 + K2MnO4 2). Finding atoms
Hydrolysis
Hydrolysis is a process of exchange interaction between salt ions and water, leading to the formation of slightly dissociated substances and accompanied by a change in the reaction (pH) of the medium. The essence
Rate of chemical reactions
The reaction rate is determined by a change in the molar concentration of one of the reactants: V = ± ((C2 – C1) / (t2 - t
Factors affecting the rate of chemical reactions
1. The nature of the reacting substances. The nature of the chemical bonds and the structure of the reagent molecules play an important role. Reactions proceed in the direction of destruction of less strong bonds and the formation of substances with
Activation energy
The collision of chemical particles leads to a chemical interaction only if the colliding particles have energy exceeding some specific value. Let's consider each other
Catalysis catalyst
Many reactions can be accelerated or slowed down by the introduction of certain substances. The added substances do not participate in the reaction and are not consumed during its course, but have a significant effect on
Chemical equilibrium
Chemical reactions that proceed at comparable rates in both directions are called reversible. In such reactions, equilibrium mixtures of reagents and products are formed, the composition of which
Le Chatelier's principle
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Factors influencing the rate of a chemical reaction
Factors influencing the rate of a chemical reaction Increase the speed Reduce the speed Presence of chemically active reagents
Hess's law
Using table values
Thermal effect
During the reaction, bonds in the starting substances are broken and new bonds are formed in the reaction products. Since the formation of a bond occurs with the release, and its breaking occurs with the absorption of energy, then x
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, white solution. 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.