Oxidation state and valence of chemical elements. Unified State Examination chemistry tasks: Electronegativity. Oxidation state and valence of chemical elements Nh4cl oxidation state

Mandatory minimum knowledge

Oxidation state

The patterns of changes in electronegativity in periods and groups of the Periodic System were considered in § 36.

Rules for calculating the degree of oxidation (s.o.) of chemical elements:

  1. The least electronegative chemical element is
    1. iron
    2. magnesium
    3. calcium

    You should pay attention to the phrase “least electronegative,” i.e., the element with the greatest metallic properties. This argument will allow us to exclude nitrogen, as a non-metal, from possible answers, and focus on calcium, as the most active of the metals proposed in the task. Answer: 4.

  2. The most polar chemical bond in one of the molecules
    1. CCl 4
    2. СВr 4

    Knowledge of the patterns of changes in electronegativity in the periods and groups of D. I. Mendeleev’s Periodic System allows us to exclude methane CH 4 from the list of tetravalent carbon compounds, and from the remaining halides to settle on CF 4, as a compound of carbon with the most electronegative of all chemical elements - fluorine. Answer: 2.

  3. In hydrogen chloride and chlorine molecules the chemical bond is respectively
    1. ionic and covalent polar
    2. ionic and covalent nonpolar
    3. covalent polar and covalent nonpolar
    4. hydrogen and covalent nonpolar

    The key word for quickly and correctly completing this task is the word “accordingly.” In the proposed options, only one of the answers begins with the words “polar covalent,” i.e., a bond characteristic of hydrogen chloride. Answer: 3.

  4. The oxidation state of manganese in a compound whose formula is K 2 MnO 4 is equal to

    Knowing the rules for calculating the oxidation states of elements using the formula will allow you to choose the correct answer. Answer: 3.

  5. Sulfur in salt has the lowest oxidation state
    1. potassium sulfate
    2. potassium sulfite
    3. potassium sulfide
    4. potassium hydrogen sulfate

    Obviously, quickly completing this task will be facilitated by translating the names of salts into formulas. Since sulfur is an element of group VIA, its lowest oxidation state is -2. This value corresponds to a compound with the formula K 2 S - potassium sulfide. Answer: 3.

  6. The chlorine atom has an oxidation state of +5 in the ion.
    1. С1O - 4
    2. С1O -
    3. С1O - 3
    4. С1O - 2

    When performing this task, you should pay attention to the fact that the condition does not give electrically neutral compounds, but chlorine ions with a single negative charge (“-”). Since the sum of the oxidation states of the atoms in an ion is equal to the charge of the ion, the total negative charge of the oxygen atoms in the desired ion should have a value of -6 (+5 - 6 = -1). Answer: 3.

  7. Nitrogen has an oxidation state of -3 in each of the two compounds
    1. NF 3 AND NH 3
    2. NH 4 Cl and N 2 O 3
    3. NH 4 Cl and NH 3
    4. HNO2 and NF3

    To determine the correct answer, you need to mentally divide the answer options into left and right columns. Then select the one in which the compounds have a simpler composition - in our case, this is the right sub-column of binary compounds. The analysis will eliminate answers 2 and 4, since in oxide and fluoride nitrogen has a positive oxidation state, like a less electronegative element. This argument allows us to exclude answer 1, since the first substance in it is still the same nitrogen fluoride. Answer: 3.

  8. Do not belong to substances of molecular structure
    1. carbon dioxide
    2. methane
    3. hydrogen chloride
    4. calcium carbonate

    You should pay attention to the negative judgment embedded in the task conditions. Since gaseous substances under normal conditions have a molecular crystal lattice in the solid state, options 1-3 do not meet the conditions of the task. Classifying calcium carbonate as a salt will once again confirm the correct answer. Answer: 4.

  9. Are the following judgments about the properties of substances and their structure correct?

    A. Wet laundry dries in the cold because substances of molecular structure are capable of sublimation (sublimation).

    B. Wet laundry dries out in the cold because water molecules have a low molecular weight.

    1. only A is correct
    2. only B is correct
    3. both judgments are correct
    4. both statements are incorrect

    Knowledge of the physical properties of substances of molecular structure allows us to decide that the reason for wet laundry drying out in the cold is the ability of ice to sublimate, and not the dipole structure of water molecules. Answer: 1.

  10. Each of the substances whose formulas are given in the series has a molecular structure
    1. CO 2, HNO 3, CaO
    2. Na 2 S, Br 2, NO 2
    3. H 2 SO 4, Cu, O 3
    4. SO 2, I 2, HCl

    Since the proposed options contain three substances each, it is logical to mentally divide these options into three vertical columns. Analysis of each of them, starting with substances of a simpler composition (middle column), will allow us to exclude answer 3, since it contains the metal copper, which has a metallic crystal lattice. A similar analysis of the right sub-column will allow us to exclude answer 1, since it contains an alkaline earth metal oxide (ionic lattice). Of the two remaining options, it is necessary to exclude option 2, since it contains an alkali metal salt - sodium sulfide (ionic lattice). Answer: 4.

Tasks for independent work

  1. Nitrogen exhibits oxidation state +5 in a compound whose formula is
    1. N2O5
    2. N2O4
    3. N2O
  2. The oxidation state of chromium in a compound whose formula is (NH 4) 2 Cr 2 O 7 is equal to
  3. The degree of oxidation of nitrogen decreases in a number of substances whose formulas are
    1. NH3, NO2, KNO3
    2. N2O4, KNO2, NH4Cl
    3. N2,N2O,NH3
    4. HNO3, HNO2, NO2
  4. The oxidation state of chlorine increases in a number of substances whose formulas are
    1. HClO, HClO 4, KClO 3
    2. Сl 2, С1 2 O 7, КСlO 3
    3. Ca(C1O) 2, KClO 3, HClO 4
    4. KCl, KClO 3, KClO
  5. The most polar chemical bond in a molecule
    1. ammonia
    2. hydrogen sulfide
    3. hydrogen bromide
    4. hydrogen fluoride
  6. Substance with a covalent nonpolar bond
    1. white phosphorus
    2. aluminum phosphide
    3. phosphorus(V) chloride
    4. calcium phosphate
  7. Formulas of substances with only ionic bonds are written in the series
    1. sodium chloride, phosphorus (V) chloride, sodium phosphate
    2. sodium oxide, sodium hydroxide, sodium peroxide
    3. carbon disulfide, calcium carbide, calcium oxide
    4. calcium fluoride, calcium oxide, calcium chloride
  8. Has an atomic crystal lattice
    1. sodium oxide
    2. calcium oxide
    3. sulfur(IV) oxide
    4. aluminium oxide
  9. A compound with an ionic crystal lattice is formed when chlorine interacts with
    1. phosphorus
    2. barium
    3. hydrogen
    4. gray
  10. Are the following statements about ammonium chloride correct?

    A. Ammonium chloride is a substance of ionic structure, formed due to covalent polar and ionic bonds.

    B. Ammonium chloride is a substance of ionic structure, and therefore solid, refractory and non-volatile.

    1. only A is correct
    2. only B is correct
    3. both judgments are correct
    4. both judgments are wrong

DEFINITION

Ammonium chloride(ammonia) under normal conditions appears as white crystals (Fig. 1).

Volatile, little thermally stable (melting point - 400 o C under pressure). Gross formula - NH 4 Cl. The molar mass of ammonium chloride is 53.49 g/mol.

Rice. 1. Ammonium chloride. Appearance.

It is highly soluble in water (hydrolyzes into the cation). Does not form crystalline hydrates. Decomposes with concentrated sulfuric acid and alkalis.

NH4Cl, oxidation states of elements in it

To determine the oxidation states of the elements that make up ammonium chloride, you first need to understand for which elements this value is precisely known.

The degree of oxidation of an acid residue is determined by the number of hydrogen atoms included in the acid that forms it, indicated with a minus sign. Chloride ion is the acidic residue of hydrochloric (hydrochloric) acid, the formula of which is HCl. It contains one hydrogen atom, therefore, the oxidation state of chlorine in the chloride ion is (-1).

Ammonium ion is a derivative of ammonia (NH 3), which is a hydride. And, as is known, the oxidation state of hydrogen in hydrides is always equal to (+1). To find the oxidation state of nitrogen, we take its value as “x” and determine it using the electrical neutrality equation:

x + 4× (+1) + (-1) = 0;

x + 4 - 1 = 0;

This means the oxidation state of nitrogen in ammonium chloride is (-3):

N -3 H +1 4 Cl -1 .

Examples of problem solving

EXAMPLE 1

Exercise Determine the oxidation degree of nitrogen in the following compounds: a) NH 3 ; b) Li 3 N; c) NO 2.
Answer a) Ammonia is a nitrogen hydride, and, as is known, in these compounds hydrogen exhibits an oxidation state (+1). To find the oxidation state of nitrogen, we take its value as “x” and determine it using the electrical neutrality equation:

x + 3× (+1) = 0;

The oxidation degree of nitrogen in ammonia is (-3): N -3 H 3 .

b) Lithium exhibits a constant oxidation state that coincides with the group number in the Periodic Table of D.I. Mendeleev, in which it is located, i.e. equal to (+1) (lithium - metal). To find the oxidation state of nitrogen, we take its value as “x” and determine it using the electrical neutrality equation:

3× (+1) + x = 0;

The oxidation state of nitrogen in lithium nitride is (-3): Li 3 N -3.

c) The oxidation degree of oxygen in the composition of oxides is always equal to (-2). To find the oxidation state of nitrogen, we take its value as “x” and determine it using the electrical neutrality equation:

x + 2×(-2) = 0;

The oxidation state of nitrogen in nitrogen dioxide is (+4): N +4 O 2 .

EXAMPLE 2

Exercise Determine the oxidation degree of nitrogen in the following compounds: a) N 2; b) HNO 3; c) Ba(NO 2) 2.
Answer a) In compounds with non-polar bonds, the oxidation state of elements is zero. This means that the oxidation state of nitrogen in its diatomic molecule is zero: N 0 2.

b) The oxidation states of hydrogen and oxygen in the composition of inorganic acids are always equal to (+1) and (-2), respectively. To find the oxidation state of nitrogen, we take its value as “x” and determine it using the electrical neutrality equation:

(+1) + x + 3×(-2) = 0;

1 + x - 6 = 0;

The oxidation degree of nitrogen in nitric acid is (+5): HN +5 O 3 .

c) Barium exhibits a constant oxidation state that coincides with the group number in the D.I. Periodic Table. Mendeleev, in which it is located, i.e. equal to (+2) (barium is a metal). The oxidation degree of oxygen in the composition of inorganic acids and their residues is always equal to (-2). To find the oxidation state of nitrogen, we take its value as “x” and determine it using the electrical neutrality equation:

(+2) + 2×x + 4×(-2) = 0;

2 + 2x - 8 = 0;

The oxidation state of nitrogen in barium nitrite is (+3): Ba(N +3 O 2) 2.

Electronegativity. Oxidation state and valence of chemical elements.

Redox reactions.

1) Establish a correspondence between the scheme for changing the oxidation state of an element and the equation of the reaction in which this change occurs.

3) Establish a correspondence between the equation of the redox reaction and the property of nitrogen that it exhibits in this reaction.

4) Establish a correspondence between the formula of a substance and the oxidation state of chlorine in it.

6) Establish a correspondence between the properties of nitrogen and the equation of the redox reaction in which it exhibits these properties.

7) Establish a correspondence between the formula of a substance and the degree of oxidation of nitrogen in it.

FORMULA OF THE SUBSTANCE
A) NaNO 2		 NITROGEN OXIDATION RATE
1) +5
2) +3
3) –3, +5
4) 0, +2
5) –3, +3
6) +4, +2

8) Establish a correspondence between the reaction scheme and the change in the oxidation state of the oxidizing agent in it.

10. Establish a correspondence between the formula of the salt and the oxidation state of chromium in it.

12. Establish a correspondence between the reaction scheme and the formula of the reducing agent in it

14. Establish a correspondence between the formula of a substance and the degree of oxidation of nitrogen in it.

16. Establish a correspondence between the formula of the salt and the oxidation state of chromium in it.

18. Establish a correspondence between the reaction scheme and the formula of the reducing agent in it

19. Establish a correspondence between the reaction scheme and the change in the oxidation state of the reducing agent.

REACTION SCHEME

A) Cl 2 + P → PCl 5

B) HCl + KMnO 4 → Cl 2 + MnCl 2 + KCl + H 2 O

B) HClO + H 2 O 2 → O 2 + H 2 O + HCl

D) Cl 2 + KOH → KCl + KClO 3 + H 2 O

 CHANGE FROM RESTORER
1) Cl 0 → Cl -1

2) Cl -1 →Cl 0

3) Cl 0 → Cl +1

 5) Cl 0 → Cl +5

6) Mn +7 → Mn +2

20. Establish a correspondence between the reaction scheme and the change in the oxidation state of the oxidizing agent.

REACTION SCHEME

A) Na 2 SO 3 + I 2 + NaOH → Na 2 SO 4 + NaI + H 2 O

B) I 2 + H 2 S → S + HI

B) SO 2 + NaIO 3 + H 2 O → H 2 SO 4 + NaI

D) H 2 S + SO 2 → S + H 2 O

 CHANGE FROM OXIDIZER
1) S -2 → S 0

3) S +4 → S +6

 5) I +5 → I -1

21. Establish a correspondence between the reaction scheme and the change in the oxidation state of the reducing agent.

23. Establish a correspondence between the formula of a substance and the oxidation state of chromium in it.

25. Establish a correspondence between the reaction scheme and the change in the oxidation state of the reducing agent.

27. Establish a correspondence between the reaction scheme and the change in the oxidation state of the oxidizing agent.



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