Reactions going with a change in the degree of oxidation. Redox reactions
Task number 1
Establish a correspondence between the reaction equation and the property of the nitrogen element that it exhibits in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
Answer: 4221
Explanation:
A) NH 4 HCO 3 - salt, which includes the ammonium cation NH 4 +. In the ammonium cation, nitrogen always has an oxidation state of -3. As a result of the reaction, it turns into ammonia NH 3. Hydrogen almost always (except for its compounds with metals) has an oxidation state of +1. Therefore, for the ammonia molecule to be electrically neutral, nitrogen must have an oxidation state of -3. Thus, there is no change in the degree of nitrogen oxidation; it does not exhibit redox properties.
B) As already shown above, nitrogen in ammonia NH 3 has an oxidation state of -3. As a result of the reaction with CuO, ammonia is converted into a simple substance N 2. In any simple substance, the oxidation state of the element with which it is formed is equal to zero. Thus, the nitrogen atom loses its negative charge, and since electrons are responsible for the negative charge, this means that they are lost by the nitrogen atom as a result of the reaction. An element that loses some of its electrons in a reaction is called a reducing agent.
C) As a result of the reaction, NH 3 with an oxidation state of nitrogen equal to -3 turns into nitric oxide NO. Oxygen almost always has an oxidation state of -2. Therefore, in order for the nitric oxide molecule to be electrically neutral, the nitrogen atom must have an oxidation state of +2. This means that the nitrogen atom changed its oxidation state from -3 to +2 as a result of the reaction. This indicates the loss of 5 electrons by the nitrogen atom. That is, nitrogen, as in the case of B, is a reducing agent.
D) N 2 is a simple substance. In all simple substances, the element that forms them has an oxidation state of 0. As a result of the reaction, nitrogen is converted into lithium nitride Li3N. The only oxidation state of an alkali metal other than zero (any element has an oxidation state of 0) is +1. Thus, for the Li3N structural unit to be electrically neutral, nitrogen must have an oxidation state of -3. It turns out that as a result of the reaction, nitrogen acquired a negative charge, which means the addition of electrons. Nitrogen is the oxidizing agent in this reaction.
Task number 2
Establish a correspondence between the reaction scheme and the property of the phosphorus element that it exhibits in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
Write in the table the selected numbers under the corresponding letters.
Answer: 1224
Task number 3
| REACTION EQUATION | |
| A) 4NH 3 + 5O 2 → 4NO + 6H 2 O B) 2Cu(NO 3) 2 → 2CuO + 4NO 2 + O 2 C) 4Zn + 10HNO 3 → NH 4 NO 3 + 4Zn (NO 3) 2 + 3H 2 O D) 3NO 2 + H 2 O → 2HNO 3 + NO |
Write in the table the selected numbers under the corresponding letters.
Answer: 1463
Task number 4
Establish a correspondence between the reaction equation and the change in the oxidation state of the oxidizing agent in it: for each position indicated by a letter, select the corresponding position indicated by a number.
| REACTION EQUATION | CHANGING THE OXIDIZER DEGREE |
| A) SO 2 + NO 2 → SO 3 + NO B) 2NH 3 + 2Na → 2NaNH 2 + H 2 C) 4NO 2 + O 2 + 2H 2 O → 4HNO 3 D) 4NH 3 + 6NO → 5N 2 + 6H 2 O |
Write in the table the selected numbers under the corresponding letters.
Answer: 3425
Task number 5
Establish a correspondence between the reaction scheme and the coefficient in front of the oxidizing agent in it: for each position indicated by a letter, select the corresponding position indicated by a number.
| REACTION SCHEME | COEFFICIENT BEFORE THE OXIDIZER |
| A) NH 3 + O 2 → N 2 + H 2 O B) Cu + HNO 3 (conc.) → Cu(NO 3) 2 + NO 2 + H 2 O C) C + HNO 3 → NO 2 + CO 2 + H 2 O D) S + HNO 3 → H 2 SO 4 + NO |
Write in the table the selected numbers under the corresponding letters.
Answer: 3442
Task number 6
Establish a correspondence between the reaction equation and the change in the oxidation state of the oxidizing agent in it: for each position indicated by a letter, select the corresponding position indicated by a number.
| REACTION EQUATION | CHANGING THE OXIDIZER DEGREE |
| A) 2NH 3 + K → 2KNH 2 + H 2 B) H 2 S + K → K 2 S + H 2 C) 4NH 3 + 6NO → 5N 2 + 6H 2 O D) 2H 2 S + 3O 2 → 2SO 2 + 2H 2 O |
Write in the table the selected numbers under the corresponding letters.
Answer: 4436
Task number 7
Establish a correspondence between the starting materials and the property of copper that this element exhibits in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
Write in the table the selected numbers under the corresponding letters.
Answer: 2124
Task number 8
Establish a correspondence between the reaction scheme and the property of sulfur that it exhibits in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
Write in the table the selected numbers under the corresponding letters.
Answer: 3224
Task number 9
Establish a correspondence between the reaction scheme and the property of phosphorus that it exhibits in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
Write in the table the selected numbers under the corresponding letters.
Answer: 3242
Task number 10
Establish a correspondence between the reaction scheme and the property of nitrogen that it exhibits in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
Write in the table the selected numbers under the corresponding letters.
Answer: 2141
Task number 11
Establish a correspondence between the reaction scheme and the property of fluorine that it exhibits in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
Write in the table the selected numbers under the corresponding letters.
Answer: 1444
Task number 12
Establish a correspondence between the reaction scheme and the change in the oxidation state of the reducing agent: for each position indicated by a letter, select the corresponding position indicated by a number.
| REACTION SCHEME | |
| A) NaIO → NaI + NaIO 3 B) HI + H 2 O 2 → I 2 + H 2 O C) NaIO 3 → NaI + O 2 D) NaIO 4 → NaI + O 2 | 1) I +5 → I −1 2) O −2 → O 0 3) I +7 →I −1 4) I +1 → I −1 5) I +1 → I +5 6) I −1 → I 0 |
Write in the table the selected numbers under the corresponding letters.
Answer: 5622
Task number 13
Establish a correspondence between the reaction equation and the change in the oxidation state of the reducing agent in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
| REACTION EQUATION | CHANGING THE OXIDATION DEGREE OF THE REDUCER |
| A) H 2 S + I 2 → S + 2HI B) Cl 2 + 2HI → I 2 + 2HCl C) 2SO 3 + 2KI → I 2 + SO 2 + K 2 SO 4 D) S + 3NO 2 → SO 3 + 3NO |
Write in the table the selected numbers under the corresponding letters.
Answer: 5331
Task number 14
Establish a correspondence between the redox reaction equation and the change in the oxidation state of sulfur in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
| REACTION EQUATION | CHANGES IN THE OXIDATION STATE OF SULFUR |
| A) S + O 2 → SO 2 B) SO 2 + Br 2 + 2H 2 O → H 2 SO 4 + 2HBr C) C + H 2 SO 4 (conc.) → CO 2 + 2SO 2 + 2H 2 O D) 2H 2 S + O 2 → 2H 2 O + 2S |
Write in the table the selected numbers under the corresponding letters.
Answer: 4123
Task number 15
| CHANGING THE OXIDATION DEGREE | SUBSTANCE FORMULA |
| A) S -2 → S +4 B) S −2 → S +6 C) S +6 → S −2 D) S −2 → S 0 | 1) Cu 2 S and O 2 2) H 2 S and Br 2 (solution) 3) Mg and H 2 SO 4 (conc.) 4) H 2 SO 3 and O 2 5) PbS and HNO 3 (conc.) 6) C and H 2 SO 4 (conc.) |
Write in the table the selected numbers under the corresponding letters.
Answer: 1532
Task number 16
Establish a correspondence between the change in the oxidation state of sulfur in the reaction and the formulas of the starting substances that enter into it: for each position indicated by a letter, select the corresponding position indicated by a number.
| CHANGING THE OXIDATION DEGREE | SUBSTANCE FORMULA |
| A) S 0 → S +4 B) S +4 → S +6 C) S −2 → S 0 D) S +6 → S +4 | 1) Cu and H 2 SO 4 (diff.) 2) H 2 S and O 2 (insufficient) 3) S and H 2 SO 4 (conc.) |
Write in the table the selected numbers under the corresponding letters.
Answer: 3523
Task number 17
Establish a correspondence between the properties of nitrogen and the equation of the redox reaction in which it exhibits these properties: for each position indicated by a letter, select the corresponding position indicated by a number.
Write in the table the selected numbers under the corresponding letters.
Answer: 2143
Task number 18
Establish a correspondence between the change in the oxidation state of chlorine in the reaction and the formulas of the starting substances that enter into it: for each position indicated by a letter, select the corresponding position indicated by a number.
| CHANGING THE OXIDATION DEGREE | FORMULA OF STARTING SUBSTANCES |
| A) Cl 0 → Cl -1 B) Cl -1 → Cl 0 C) Cl +5 → Cl -1 D) Cl 0 → Cl +5 | 1) KClO 3 (heating) 2) Cl 2 and NaOH (hot solution) 3) KCl and H 2 SO 4 (conc.) 6) KClO 4 and H 2 SO 4 (conc.) |
Write in the table the selected numbers under the corresponding letters.
Answer: 2412
Task #19
Establish a correspondence between the formula of an ion and its ability to exhibit redox properties: for each position indicated by a letter, select the corresponding position indicated by a number.
Write in the table the selected numbers under the corresponding letters.
Answer: 2332
Task number 20
Establish a correspondence between the chemical reaction scheme and the change in the oxidation state of the oxidizing agent: for each position indicated by a letter, select the corresponding position indicated by a number.
| REACTION SCHEME | CHANGING THE OXIDIZER DEGREE |
| A) MnCO 3 + KClO 3 → MnO 2 + KCl + CO 2 B) Cl 2 + I 2 + H 2 O → HCl + HIO 3 C) H 2 MnO 4 → HMnO 4 + MnO 2 + H 2 O D) Na 2 SO 3 + KMnO 4 + KOH → Na 2 SO 4 + K 2 MnO 4 + H 2 O | 1) Cl 0 → Cl - 2) Mn+6 → Mn+4 3) Cl+5 → Cl- 4) Mn +7 → Mn +6 5) Mn+2 → Mn+4 6) S+4 → S+6 |
Write in the table the selected numbers under the corresponding letters.
Answer: 3124
Task number 21
Establish a correspondence between the reaction scheme and the change in the oxidation state of the reducing agent in this reaction: for each position indicated by a letter, select the corresponding position indicated by a number.
Redox reactions (ORD) - reactions that occur with a change in the oxidation state of the atoms that make up the reactants, as a result of the transfer of electrons from one atom to another.
Oxidation state – the formal charge of an atom in a molecule, calculated on the assumption that the molecule consists only of ions.
The most electronegative elements in the compound have negative oxidation states, and the atoms of elements with less electronegativity are positive.
The oxidation state is a formal concept; in some cases, the oxidation state does not coincide with the valency.
For example: N 2 H 4 (hydrazine)
nitrogen oxidation state - -2; nitrogen valence - 3.
Calculation of the degree of oxidation
To calculate the oxidation state of an element, the following provisions should be taken into account:
1. The oxidation states of atoms in simple substances are equal to zero (Na 0; H 2 0).
2. The algebraic sum of the oxidation states of all atoms that make up the molecule is always zero, and in a complex ion this sum is equal to the charge of the ion.
3. Atoms have a constant oxidation state: alkali metals (+1), alkaline earth metals (+2), hydrogen (+1) (except for hydrides NaH, CaH 2, etc., where the oxidation state of hydrogen is -1), oxygen (-2 ) (except for F 2 -1 O +2 and peroxides containing the –O–O– group, in which the oxidation state of oxygen is -1).
4. For elements, the positive oxidation state cannot exceed a value equal to the group number of the periodic system.
V 2 +5 O 5 -2; Na 2 +1 B 4 +3 O 7 -2; K +1 Cl +7 O 4 -2; N -3 H 3 +1; K 2 +1 H +1 P +5 O 4 -2; Na 2 +1 Cr 2 +6 O 7 -2
Reactions with and without change in oxidation state
There are two types of chemical reactions:
A Reactions in which the oxidation state of the elements does not change:
Addition reactions: SO 2 + Na 2 O Na 2 SO 3
Decomposition reactions: Cu(OH) 2 CuO + H 2 O
Exchange reactions: AgNO 3 + KCl AgCl + KNO 3
NaOH + HNO 3 NaNO 3 + H 2 O
B Reactions in which there is a change in the oxidation states of the atoms of the elements that make up the reacting compounds:
2Mg 0 + O 2 0 2Mg +2 O -2
2KCl +5 O 3 -2 – t 2KCl -1 + 3O 2 0
2KI -1 + Cl 2 0 2KCl -1 + I 2 0
Mn +4 O 2 + 4HCl -1 Mn +2 Cl 2 + Cl 2 0 + 2H 2 O
Such reactions are called redox reactions. .
Oxidation, reduction
In redox reactions, electrons are transferred from one atom, molecule, or ion to another. Electron donation process - oxidation. When oxidized, the oxidation state increases:
H 2 0 − 2ē 2H +
S -2 − 2ē S 0
Al 0 − 3ē Al +3
Fe +2 - ē Fe +3
2Br - − 2ē Br 2 0
The process of electron addition - − recovery. When reduced, the oxidation state decreases.
Mn +4 + 2ē Mn +2
Cr +6 +3ē Cr +3
Cl 2 0 +2ē 2Cl -
O 2 0 + 4ē 2O -2
Atoms or ions that gain electrons in this reaction are oxidizing agents, and those that donate electrons are reducing agents.
Redox properties of a substance and the degree of oxidation of its constituent atoms
Compounds containing atoms of elements with a maximum degree of oxidation can only be oxidizing agents due to these atoms, because they have already given up all their valence electrons and are only able to accept electrons. The maximum oxidation state of an atom of an element is equal to the number of the group in the periodic table to which the element belongs. Compounds containing atoms of elements with a minimum degree of oxidation can only serve as reducing agents, since they are only capable of donating electrons, because the external energy level of such atoms is completed by eight electrons. The minimum oxidation state of metal atoms is 0, for non-metals - (n–8) (where n is the group number in the periodic system). Compounds containing atoms of elements with an intermediate oxidation state can be both oxidizing and reducing agents, depending on the partner with which they interact and on the reaction conditions.
Redox reactions include those that are accompanied by the movement of electrons from one particle to another. When considering the patterns of the course of redox reactions, the concept of the degree of oxidation is used.
Oxidation state
concept oxidation states introduced to characterize the state of elements in compounds. The oxidation state is conditional charge of an atom in a compound, calculated assuming that the compound is made up of ions. The oxidation state is indicated by an Arabic numeral with a plus sign when electrons are shifted from a given atom to another atom, and a minus digit when electrons are shifted in the opposite direction. A number with a “+” or “-“ sign is placed above the element symbol. The oxidation state indicates the oxidation state of an atom and is just a convenient form for accounting for electron transfer: it should not be considered as the effective charge of an atom in a molecule (for example, in the LiF molecule, the effective charges of Li and F are respectively + 0.89 and -0, 89, while the oxidation states are +1 and -1), or as the valence of the element (for example, in the compounds CH 4, CH 3 OH, HCOOH, CO 2, the carbon valency is 4, and the oxidation states are respectively -4, -2, + 2, +4). The numerical values of valency and oxidation state can coincide in absolute value only when compounds with an ionic structure are formed.
When determining the degree of oxidation, the following rules are used:
Atoms of elements that are in a free state or in the form of molecules of simple substances have an oxidation state equal to zero, for example, Fe, Cu, H 2 , N 2, etc.
The oxidation state of an element in the form of a monatomic ion in a compound having an ionic structure is equal to the charge of this ion,
1 -1 +2 -2 +3 -1
for example, NaCl, Cu S, AlF 3 .
Hydrogen in most compounds has an oxidation state of +1, with the exception of metal hydrides (NaH, LiH), in which the oxidation state of hydrogen is -1.
The most common oxygen oxidation state in compounds is -2, with the exception of peroxides (Na 2 O 2, H 2 O 2), in which the oxygen oxidation state is -1 and F 2 O, in which the oxygen oxidation state is +2.
For elements with a variable oxidation state, its value can be calculated knowing the formula of the compound and taking into account that the algebraic sum of the oxidation states of all elements in a neutral molecule is zero. In a complex ion, this sum is equal to the charge of the ion. For example, the oxidation state of the chlorine atom in the HClO 4 molecule, calculated from the total charge of the molecule = 0, where x is the oxidation state of the chlorine atom), is +7. The oxidation state of the sulfur atom in the ion (SO 4) 2- [x + 4 (-2) \u003d -2] is +6.
Redox properties of substances
Any redox reaction consists of oxidation and reduction processes. Oxidation - is the process of donating electrons by an atom, ion or molecule of a reactant. Substances that give their electrons during the reaction and are oxidized at the same time, they are called reducing agents.
Recovery is the process of accepting electrons by an atom, ion or molecule of the reactant.
Substances that accept electrons and are reduced in the process are called oxidizing agents.
Oxidation-reduction reactions always proceed as a single process, called redox reaction. For example, in the interaction of metallic zinc with copper ions reducing agent(Zn) donates its electrons oxidizing agent– copper ions (Cu 2+):
Zn + Cu2+ Zn2+ + Cu
Copper is released on the surface of zinc, and zinc ions go into solution.
The redox properties of elements are associated with the structure of their atoms and are determined by the position in the periodic system of D.I. Mendeleev. The reducing ability of an element is due to the weak bond of valence electrons with the nucleus. Metal atoms containing a small number of electrons at the external energy level are prone to their return, i.e. easily oxidized, playing the role of reducing agents. The strongest reducing agents are the most active metals.
The criterion for the redox activity of elements can be the value of their relative electronegativity: the higher it is, the more pronounced the oxidizing ability of the element, and the lower, the more pronounced its reducing activity. Non-metal atoms (for example, F, O) have a high electron affinity and relative electronegativity, they easily accept electrons, i.e. are oxidizing agents.
The redox properties of an element depend on the degree of its oxidation. The same element has lower, higher and intermediate oxidation states.
As an example, consider sulfur S and its compounds H 2 S, SO 2 and SO 3. The relationship between the electronic structure of the sulfur atom and its redox properties in these compounds is clearly shown in Table 1.
In the H 2 S molecule, the sulfur atom has a stable octet configuration of the external energy level 3s 2 3p 6 and therefore can no longer add electrons, but can give them away.
The state of an atom in which it can no longer accept electrons is called the lowest oxidation state.
In the lowest oxidation state, the atom loses its oxidizing ability and can only be a reducing agent.
Table 1.
|
Substance formula |
Electronic formula |
redox properties |
|
|
|
1s 2 2s 2 2p 6 3s 2 3p 6 |
|
|
|
|
1s 2 2s 2 2p 6 3s 2 3p 4 |
oxidizing agent |
reducing agent |
|
|
1s 2 2s 2 2p 6 3s 2 3p o |
oxidizing agent |
|
|
|
1s 2 2s 2 2p 6 3s o 3p 0 |
oxidizing agent |
|
–2
;
- 6
;
- 8
reducing agent
+
2
–4
;
-
6
+
4 
;
+
6
-2
reducing agent
+
2
;
+ 6
;
+
8
In the SO 3 molecule, all the outer electrons of the sulfur atom are displaced to the oxygen atoms. Therefore, in this case, the sulfur atom can only accept electrons, exhibiting oxidizing properties.
The state of an atom in which it has donated all its valence electrons is called the highest oxidation state. An atom in the highest oxidation state can only be an oxidizing agent.
In the SO 2 molecule and elemental sulfur S, the sulfur atom is located in intermediate oxidation states, i.e., having valence electrons, an atom can give them away, but, without having a completed R - sublevel, and can accept electrons before its completion.
An atom of an element that has an intermediate oxidation state can exhibit both oxidizing and reducing properties, which is determined by its role in a particular reaction.
So, for example, the role of sulfite anion SO 
different in the following reactions:
5Na 2 SO 3 + 2KMnO 4 + 3H 2 SO 4 2MnSO 4 + 5Na 2 SO 4 + K 2 SO 4 + 3H 2 O (1)
H 2 SO 3 + 2 H 2 S 3 S + 3 H 2 O (2)
In reaction (1), the sulfite anion SO 
in the presence of a strong oxidizing agent, KMnO 4 plays the role of a reducing agent; in reaction (2) sulfite anion SO 
- an oxidizing agent, since H 2 S can only exhibit reducing properties.
Thus, among complex substances reducing agents can be:
1. Simple substances whose atoms have low ionization energies and electronegativity (in particular, metals).
2. Complex substances containing atoms in lower oxidation states:
H Cl,H2 S,N H3
Na 2 S O 3 , Fe Cl2, sn(NO 3) 2 .
Oxidizers can be:
1. Simple substances whose atoms have high values of electron affinity and electronegativity - non-metals.
2. Complex substances containing atoms in higher oxidation states: +7 +6 +7
K Mn O 4 , K 2 Cr 2 O 7 , HClO 4 .
3. Complex substances containing atoms in intermediate oxidation states:
Na 2 S O 3 , Mn O 2 , Mn SO4.
There are two types of chemical reactions:
A Reactions in which the oxidation state of the elements does not change:
Addition reactions
SO 2 + Na 2 O \u003d Na 2 SO 3
Decomposition reactions
Cu(OH) 2 \u003d CuO + H 2 O
Exchange reactions
AgNO 3 + KCl = AgCl + KNO 3
NaOH + HNO 3 \u003d NaNO 3 + H 2 O
B Reactions in which there is a change in the oxidation states of the atoms of the elements that make up the reacting compounds and the transfer of electrons from one compound to another:
2Mg 0 + O 2 0 \u003d 2Mg +2 O -2
2KI -1 + Cl 2 0 = 2KCl -1 + I 2 0
Mn +4 O 2 + 4HCl -1 \u003d Mn +2 Cl 2 + Cl 2 0 + 2H 2 O
Such reactions are called redox reactions.
The oxidation state is the conditional charge of an atom in a molecule, calculated on the assumption that the molecule consists of ions and is generally electrically neutral.
The most electronegative elements in a compound have negative oxidation states, while the atoms of elements with less electronegativity are positive.
The degree of oxidation is a formal concept; in some cases, the oxidation state does not coincide with the valency.
for example:
N 2 H 4 (hydrazine)
nitrogen oxidation state - -2; nitrogen valence - 3.
Calculation of the degree of oxidation
To calculate the oxidation state of an element, the following provisions should be taken into account:
1. The oxidation states of atoms in simple substances are equal to zero (Na 0; H 2 0).
2. The algebraic sum of the oxidation states of all atoms that make up the molecule is always zero, and in a complex ion this sum is equal to the charge of the ion.
3. The atoms of alkali metals (+1), alkaline earth metals (+2), fluorine have a constant degree of oxidation in compounds with atoms of other elements
(-1), hydrogen (+1) (except for metal hydrides Na + H -, Ca 2+ H 2 - and others, where the oxidation state of hydrogen is -1), oxygen (-2) (except F 2 -1 O + 2 and peroxides containing the –O–O– group, in which the oxidation state of oxygen is -1).
4. For elements, the positive oxidation state cannot exceed a value equal to the group number of the periodic system.
Examples:
V 2 +5 O 5 -2; Na 2 +1 B 4 +3 O 7 -2; K +1 Cl +7 O 4 -2; N -3 H 3 +1; K 2 +1 H +1 P +5 O 4 -2; Na 2 +1 Cr 2 +6 O 7 -2
Oxidation, reduction
In redox reactions, electrons are transferred from one atom, molecule, or ion to another. The process of donating electrons is oxidation. When oxidized, the oxidation state increases:
H 2 0 - 2ē \u003d 2H + + 1 / 2O 2
S -2 - 2ē \u003d S 0
Al 0 - 3ē \u003d Al +3
Fe +2 - ē = Fe +3
2Br - - 2ē = Br 2 0
Electron addition process - reduction: When reducing, the oxidation state decreases.
Mn +4 + 2ē = Mn +2
S 0 + 2ē \u003d S -2
Cr +6 +3ē = Cr +3
Cl 2 0 +2ē \u003d 2Cl -
O 2 0 + 4ē \u003d 2O -2
Atoms, molecules or ions that gain electrons in this reaction are oxidizing agents, and those that donate electrons are reducing agents.
The oxidizing agent is reduced during the reaction, while the reducing agent is oxidized.
Redox properties of a substance and the degree of oxidation of its constituent atoms
Compounds containing atoms of elements with a maximum degree of oxidation can only be oxidizing agents due to these atoms, because they have already given up all their valence electrons and are only able to accept electrons. The maximum oxidation state of an atom of an element is equal to the number of the group in the periodic table to which the element belongs. Compounds containing atoms of elements with a minimum degree of oxidation can only serve as reducing agents, since they are only capable of donating electrons, because the external energy level of such atoms is completed by eight electrons. The minimum oxidation state for metal atoms is 0, for non-metals - (n–8) (where n is the group number in the periodic system). Compounds containing atoms of elements with an intermediate oxidation state can be both oxidizing and reducing agents, depending on the partner with which they interact and on the reaction conditions.
The most important reducing agents and oxidizing agents
Restorers
Carbon monoxide (II) (CO).
Hydrogen sulfide (H 2 S);
sulfur oxide (IV) (SO 2);
sulfurous acid H 2 SO 3 and its salts.
Hydrohalic acids and their salts.
Metal cations in lower oxidation states: SnCl 2, FeCl 2, MnSO 4, Cr 2 (SO4) 3.
Nitrous acid HNO 2 ;
ammonia NH 3 ;
hydrazine NH 2 NH 2 ;
nitric oxide (II) (NO).
cathode in electrolysis.
Oxidizers
Halogens.
Potassium permanganate (KMnO 4);
potassium manganate (K 2 MnO 4);
manganese (IV) oxide (MnO 2).
Potassium dichromate (K 2 Cr 2 O 7);
potassium chromate (K 2 CrO 4).
Nitric acid (HNO 3).
Sulfuric acid (H 2 SO 4) conc.
Copper(II) oxide (CuO);
lead(IV) oxide (PbO 2);
silver oxide (Ag 2 O);
hydrogen peroxide (H 2 O 2).
Iron(III) chloride (FeCl 3).
Berthollet's salt (KClO 3).
Anode in electrolysis.
According to the change in the oxidation state, all chemical reactions can be divided into two types:
I. Reactions occurring without changing the degree of oxidation of the elements that make up the reactants. Such reactions are referred to as ion exchange reactions.
Na 2 CO 3 + H 2 SO 4 = Na 2 SO 4 + CO 2 + H 2 O.
II. Reactions that occur with a change in the oxidation state of elements,
included in the reactants. Such reactions are referred to as redox reactions.
5NaNO 2 + 2KMnO 4 + 3H 2 SO 4 = 5NaNO 3 + 2MnSO 4 + K 2 SO 4 + 3H 2 O.
Oxidation state(oxidation) - a characteristic of the state of the atoms of the elements in the composition of the molecule. It characterizes the uneven distribution of electrons between the atoms of elements and corresponds to the charge that an atom of an element would acquire if all the common electron pairs of its chemical bonds shifted towards a more electronegative element. Depending on the relative electronegativity of the elements that form a bond, an electron pair can be shifted to one of the atoms or symmetrically located relative to the nuclei of atoms. Therefore, the oxidation state of elements can be negative, positive, or zero.
Elements whose atoms accept electrons from other atoms have a negative oxidation state. Elements whose atoms donate their electrons to other atoms have a positive oxidation state. Atoms in the molecules of simple substances have a zero oxidation state, as well as if the substance is in the atomic state.
The oxidation state is denoted +1, +2.
Ion charge 1+, 2+.
The oxidation state of an element in a compound is determined by the rules:
1. The degree of oxidation of an element in simple substances is zero.
2. Some elements in almost all of their compounds exhibit a constant oxidation state. These elements include:
It has an oxidation state of +1 (with the exception of metal hydrides).
O has an oxidation state of -2 (with the exception of fluorides).
3. Elements of groups I, II and III of the main subgroups of the Periodic Table of Elements of D.I. Mendeleev have a constant oxidation state equal to the group number.
Elements Na, Ba, Al: oxidation state +1, +2, +3, respectively.
4. For elements that have a variable oxidation state, there is the concept of higher and lower oxidation states.
The highest oxidation state of an element is equal to the group number of the Periodic Table of Elements of D.I. Mendeleev, in which the element is located.
Elements N, Cl: the highest oxidation state is +5, +7, respectively.
The lowest oxidation state of an element is equal to the group number of the Periodic Table of Elements of D.I. Mendeleev, in which the element is located minus eight.
Elements N, Cl: the lowest oxidation state is -3, -1, respectively.
5. In single-element ions, the oxidation state of the element is equal to the charge of the ion.
Fe 3+ - the oxidation state is +3; S 2- - the oxidation state is -2.
6. The sum of the oxidation states of all atoms of elements in a molecule is zero.
KNO 3 ; (+1) + X+ 3 (-2) = 0; X = +5. The oxidation state of nitrogen is +5.
7. The sum of the oxidation states of all atoms of elements in an ion is equal to the charge of the ion.
SO 4 2- ; X+ 4 (-2) = -2; X= +6. The oxidation state of sulfur is +6.
8. In compounds consisting of two elements, the element that is written on the right always has the lowest oxidation state.
Reactions in which the oxidation state of elements changes are referred to as redox reactions /ORD/. These reactions consist of oxidation and reduction processes.
Oxidation The process of donating electrons by an element that is part of an atom, molecule or ion is called.
Al 0 - 3e \u003d Al 3+
H 2 - 2e \u003d 2H +
Fe 2+ - e \u003d Fe 3+
2Cl - - 2e \u003d Cl 2
When oxidized, the oxidation state of an element increases. A substance (atom, molecule, or ion) that contains an element that donates electrons is called a reducing agent. Al, H 2 , Fe 2+ , Cl - - reducing agents. The reducing agent is oxidized.
Recovery The process of adding electrons to an element that is part of an atom, molecule or ion is called.
Cl 2 + 2e \u003d 2Cl -
Fe 3+ + e \u003d Fe 2+
When reduced, the oxidation state of an element decreases. A substance (atom, molecule, or ion) that contains an element that accepts electrons is called an oxidizing agent. S, Fe 3+, Cl 2 are oxidizing agents. The oxidant is restored.
The total number of electrons in the system during a chemical reaction does not change. The number of electrons donated by the reducing agent is equal to the number of electrons attached by the oxidizing agent.
To compile the equation of the redox reaction (ORR) in solutions, the ion-electronic method (half-reaction method) is used.
OVR can occur in acidic, neutral or alkaline environments. The reaction equations take into account the possible participation of water molecules (HOH) and those contained in the solution, depending on the nature of the medium, an excess of H + or OH - ions:
in an acidic environment - HOH and H + ions;
in a neutral environment - only HOH;
in an alkaline environment - HOH and OH - ions.
When compiling the OVR equations, it is necessary to adhere to a certain sequence:
1. Write a reaction scheme.
2. Determine the elements that have changed their oxidation state.
3. Write a diagram in a short ion-molecular form: strong electrolytes in the form of ions, weak electrolytes in the form of molecules.
4. Compose equations for the processes of oxidation and reduction (equation of half-reactions). To do this, write down the elements that change the degree of oxidation in the form of real particles (ions, atoms, molecules) and equalize the number of each element in the left and right parts of the half-reaction.
Note:
If the original substance contains fewer oxygen atoms than the products (P PO 4 3-), then the lack of oxygen is supplied by the environment.
If the original substance contains more oxygen atoms than the products (SO 4 2-SO 2), then the released oxygen is bound by the medium.
5. Equalize the left and right parts of the equations by the number of charges. To do this, add or subtract the required number of electrons.
6. Select factors for the oxidation and reduction half-reactions so that the number of electrons during oxidation is equal to the number of electrons during reduction.
7. Summarize the half-reactions of oxidation and reduction, taking into account the found factors.
8. Write down the resulting ion-molecular equation in molecular form.
9. Carry out an oxygen test.
There are three types of redox reactions:
a) Intermolecular - reactions in which the oxidation state changes for the elements that make up different molecules.
2KMnO 4 + 5NaNO 2 + 3H 2 SO 4 2MnSO 4 + 5NaNO 3 + K 2 SO 4 + 3H 2 O
b) Intramolecular - reactions in which the oxidation state changes for the elements that make up one molecule.
