Booklet on the topic of redox reactions. Presentation in chemistry on the topic "redox reactions". When metal is immersed in water...

GBOU VPO Tyumen State Medical Academy of the Ministry of Health of Russia
Department of Analytical and Organic Chemistry
General and inorganic chemistry
redox reactions
Lecture for 1st year students of the Faculty of Pharmacy

Reaction classification

2
All chemical reactions can
divided into 2 groups, one
reactions the oxidation state of atoms
remains unchanged (exchange
reactions), and in other reactions it
changes are redox reactions.
Their flow is associated with the transition
electrons from one atoms (ions) to
others.
2

The process of donating electrons is oxidation, accompanied by an increase in

decreasing negative. Process
acceptance of electrons - recovery,
accompanied by a decrease
positive oxidation state or
an increase in the negative.
3
3

Atoms, molecules or ions,
accepting electrons are called
oxidizers. Atoms, molecules or ions,
donating electrons are called
reducing agents.
Oxidation is always accompanied
recovery. Redox reactions are
is the unity of two opposite
processes - oxidation and reduction.
4

Oxidizers are:

simple substances whose atoms have
high electronegativity. it
elements of VII, VI, V groups of the main subgroups, of which
the most active are fluorine, oxygen, chlorine.
complex substances whose cations are in
the highest degree of oxidation.
For example: SnCl4, FeCl3, CuSO4.
complex substances, in the anions of which the atom
metal or non-metal are in the highest
oxidation states
For example: K2Cr2O7, KMnO4, KNO3, H2SO4.
5
5

Restorers are:

Elements of groups I, II, III of the main subgroups. For example:
Na, Zn, H2, Al.
Compounds whose cations are in
lowest degree of oxidation. For example: SnCl2, FeCl2.
Complex substances in which anions reach
limiting negative oxidation state.
For example:
KI, H2S, NH3.
Substances whose ions are in intermediate
oxidation states can be both an oxidizing agent and
reducing agent For example: Na2SO3 .
The measure of reducing properties is the value
ionization energy (this is the energy required for
6sequential separation of electrons from the atom.)6

Three types of redox reactions.

Three types of redox reactions.
- intermolecular,
- intramolecular,
- disproportionation
- In intermolecular OVR
elements
The oxidizing agent and reducing agent are in
different substances. For example:
SnCl2 + 2FeCl3 → SnCl4 + 2FeCl2
2 Fe 3+ + e \u003d Fe 2+
- recovery
1 Sn 2+ - 2e = Sn 4+
- oxidation
7

Intramolecular
reactions
occur with a change in degree
oxidation of different atoms in the same
the same molecule. For example:
2 KClO3 → 2KCl + 3O2
2 Cl5+ + 6e = Cl 3 2O2- - 4e- = O2
8
- recovery
- oxidation
8

Disproportionation reactions

proceed at the same time
decrease and increase
oxidation states of atoms of one
and the same element.
3HNO2 → HNO3 + 2NO + H2O
2 N 3+ + e = N 2+ - recovery
1 N 3+ - 2e = N 5+ - oxidation
9

The influence of the environment on the nature of the course of the OVR

- OVR can occur in various
environments: in acidic (excess H3O + - ions),
neutral (H2O) and alkaline (excess
OH - ions).
Depending on the environment, it may
change the nature of the reaction
between the same substances.
The environment influences the degree change
oxidation of atoms.
10

Let's look at a few examples.

KMnO4 (potassium permanganate) is
a strong oxidizing agent, in a strongly acidic
medium is reduced to Mn2+ ions,
in a neutral environment - up to MnO2 (oxide
manganese IV) and in a strongly alkaline environment
- to MnO42- (manganate ion).
1.
11

Schematically:
oxidized
the form
restored
the form
H3O+
KMnO4
H2O
HE-
Mn 2+ (colorless solution)
MnO2 (brown precipitate)
МnО42- (green solution)
12

Redox duality of hydrogen peroxide

redox
duality of hydrogen peroxide
Hydrogen peroxide as an oxidizing agent.
BUT
H–O
H+
+
HE-
2H2O
2OH-
H2O2 + 2H3O+ + 2e = 4H2O
H2O2 + 2e = 2OH-
Hydrogen peroxide as a reducing agent.
BUT
H–O
13
H+
O2 + 2H3O+ ; H2O2 - 2e + 2H2O \u003d O2 + 2H3O +
+
OH- O2 + 2H2O;
H2O2 + 2OH- - 2e \u003d O2 + 2H2O
13

Oxidizing properties of K2CrO4 and K2Cr2O7

3. Potassium chromate K2CrO4 and potassium dichromate
K2Cr2O7 are strong oxidizing agents. in sour and
alkaline solutions of the Cr(III) compound and
Cr(VI) exist in different forms.
oxidized
restored
the form
the form
Cr2O72- + H3O+
2Cr3+
CrO42- + OHCr(OH)3, CrO2-, 3
14
14

K2Cr2O7

15
15

Electron-ion balance method (half-reaction method).

Electron-ion method
balance (half-reaction method).
Reactions taking place in an acidic environment.
Rule: if the reaction proceeds in an acidic
medium, then it is possible to operate with H3O + ions
(H+) and water molecules. Ions H3O+ (H+)
write in that part of the equation
half reactions where there is an excess of oxygen,
water molecules write
respectively in the part where oxygen
no or there is a lack of it. And
the amount of H3O + (H +) is taken twice
more than the number of excess atoms
16
oxygen.

Example 1
KMnO4 + Na2SO3 + H2SO4 = MnSO4 + K2SO4 + …
OK
vos
Wednesday
Solution
2
MnO4- + 8H+ + 5e = Mn2+ + 4H2O
5
SO32- + H2O - 2e \u003d SO42- + 2H +
2MnО4- +16H++5SO32-+5Н2О=2Mn2++8H2O+5SO42- +10H+
2KMnO4 + 5Na2SO3 + 3H2SO4 = 2MnSO4 + K2SO4 + 5Na2SO4
+ 3H2O
КMnО4 – oxidizing agent, vos-sya; Na2SO3 - reducing agent, oxide
17

Example 2

Na2Cr2O7 + KBr + H2SO4 = Cr2(SO4)3 + Br2 + …
OK.
sun.
Wednesday
Solution.
1| Cr2O72- + 14H+ + 6e = 2Cr3+ + 7H2O
3| 2Br- - 2e = Br2
Cr2O72- + 14H+ + 6Br- = 2Cr3+ + 7H2O + 3Br2
Na2Cr2O7 + 6KBr + 7 H2SO4 = Cr2(SO4)3 + 3Br2 +
3 K2SO4 + Na2SO4 + 7H2O
Na2Cr2O7 - oxidant, is reduced;
18KBr - reducing agent, oxidized.
18

Reactions taking place in an alkaline medium.

Rule: if the reaction proceeds in
alkaline environment, then you can operate
OH ions and water molecules. OH ions are written in that part of the equation
half-reactions where there is a deficiency
oxygen, water molecules are written
respectively, in the part where
more oxygen. Moreover, for each
the missing oxygen atom is written
two OH- ions.
19
19

Example 1

Cr2O3 + KNO3 + KOH = K2CrO4 + KNO2 + …
sun.
OK.
Wednesday
Solution.
3 | NO3- + H2O + 2e = NO2- + 2OH1 | Cr2O3 + 10OH- -6e = 2CrO4 2- + 5H2O
3NO3-+3H2O+Cr2O3+10OH-=3NO2-+6OH-+ 2CrO42- + 5 H2O
Cr2O3 + 3KNO3 + 4 KOH = 2 K2CrO4 + 3 KNO2 + 2 H2O
Cr2O3 - reducing agent, oxidized;
KNO3 is an oxidizing agent, it is reduced.
20

Example 2

KMnO4 + Na2SO3 + KOH = K2MnO4 + Na2SO4 +
OK.
sun.
Wednesday
Solution.
…
2 | MnO4- + 1e = MnO4 21 | SO32- + 2OH- - 2e = SO4 2- + H2O
2MnO4- + SO3
2-
+ 2 OH- = 2 MnO4 2- + SO4 2- + H2O
2 KMnO4 + Na2SO3 + 2 KOH = K2MnO4 + Na2SO4 + H2O
21

Reactions taking place in a neutral environment.

22
Rule: if the reaction proceeds in a neutral environment,
should operate only with water molecules. And
excess oxygen in the oxidizing agent binds molecules
water, due to H3O + (H +) ions, for each excess atom
oxygen consumes one molecule of water, which
is placed on the left side of the half-reaction equation, in solution
OH- - ions accumulate and they are placed on the right side
half-reaction equations. lack of oxygen
the reducing agent replenishes from water molecules due to OH ions, for each missing oxygen atom,
one water molecule, which is placed on the left side
half-reaction equations, ions accumulate in the solution
H3O + (H +) and they are placed on the right side of the equation
half reactions.
22

Example 1

KMnO4 + Na2SO3 + H2O = MnO2 + Na2SO4 + …
OK.
sun.
Solution.
2 | MnO4- + 2H2O + 3e = MnO2 + 4 OH3 | SO32- + H2O -2e = SO42- + 2H+
2 MnO4-+4H2O+3SO32-+3H2O=2MnO2 +8OH- + 6H++ 3SO42
2KMnO4 + 3Na2SO3 + H2O = 2 MnO2 + 3 Na2SO4 + 2 KOH
KMnO4 - oxidizing agent, rising;
23
Na2SO3 - reducing agent, oxide
23

Example 2

MnSO4 + KMnO4 + H2O = MnO2 + K2SO4 + …
sun.
OK.
Wednesday
Solution.
2 | MnO4- + 2 H2O + 3e = MnO2 + 4 OH3 | Mn2+ + 2 H2O - 2e = MnO2 + 4 H+
2MnO4- +4H2O+3Mn2++6H2O=2MnO2+8OH-+3MnO2+12H+
3MnSO4+2KMnO4+2H2O=5MnO2+K2SO4+2H2SO4
MnSO4 - reducing agent, oxidized;
KMnO4 is an oxidizing agent, it is reduced.
24

Origin theory
equilibrium electrode and
redox
potentials
Direction detection
redox
process

The mechanism of the occurrence of the electrode potential

Me Men+ + n e

When metal is immersed in water...

Me + m H2O Men + (H2O) m + n e
Men + (H2O) m + ne Me + m H2O
Me + m H2O Men + (H2O) m +
ne

The potential established under the conditions of equilibrium of the electrode reaction is called the equilibrium electrode potential.

If a metal is immersed in a solution of its salt, then the processes occurring at the “metal-solution” boundary will be similar.

Zn
Cu
For comparison of electrode
potentials of various
metals choose
standard terms:
temperature - 250 C, pressure
- 101.3 kPa, activity
ion of the same name - 1 mol / l.
Potential difference,
arising between
metal and solution
such conditions is called
standard electrode
potential.

Standard electrode potential

The standard electrode potential (E0) is the EMF of a galvanic cell composed of a given electrode and a reference electrode. In quality

Standard electrode potential (E0) is the EMF
a galvanic cell composed of a given electrode and
reference electrode. As a reference electrode
use a normal hydrogen electrode (NHE):
H2 2H+ + 2e
Pt(H2) | 2H+
H2
platinum electrode,
plated with platinum
powder, in water
acid solution with
c(H+) = 1 mol/l and
washed by
hydrogen gas
(p = 1 atm)
at 298 K

A number of standard electrode potentials of metals

Li
Ba
Na
Zn
Fe
Pb
-3,04
-2,90
-2,71
-0,76
-0,44
-0,13
Li+
Ba2+
Na+
Zn2+
Fe2+
Pb2+
H2
0
2H+
Cu
Ag
Au
+0,34
+0,80
+1,5
Cu2+
Ag+
Au3+

Potential value in real conditions
calculated by the Nernst equation:
E Me n / Me E
0
Me n / Me
RT
ln a Me n
nF
Transition factor from ln to lg
RT
at 20 C:
2,303 0,058
F
RT
0
at 25 C:
2,303 0,059
F
0
E Me n / Me E
0
Me n / Me
0,059
lg a Me n
n

E
0
Men/Me
- standard electrode potential,
measured under standard conditions:
T 298 K
aMen 1 mol/l
F 96500 C / mol
J
R8.314
mol K

If the potential of the hydrogen electrode is known, the pH of the solution can be calculated:

E2 H / H E
2
0
2H/H2
0.059 lg aH
=0
lg a H pH
pH
E2 H / H 0
2
0,059

Silver chloride electrode (SSE)

Ag, AgCl | KCl
Electrode of the second kind
AgCl
KCl
Ag
When immersed in a solution
salts of the same name
anion its potential
will be determined
anion activity in
solution.

Ag Ag+ + e
(1)
Ks
AgCl Ag+ + Cl-
(2)
KCl K+ + Cl-
(3)
The greater the concentration of KCl, the greater the concentration of Cl-, the
less solubility of AgCl and less concentration of Ag+. in these
conditions is very small and practically undetectable. Potential,
Ag|Ag+ arising at the boundary is determined by the Nernst equation:
E x.s. E
0
Ag
Ag
RT
ln a Ag
nF

Ks a Ag aCl ; a Ag
Ex.s. E
Ex.s. E
0
Ag
0
Ag
Ag
Ag
Ks
aCl
R.T.Ks
ln
nF aCl
RT
RT
logKs
ln aCl
nF
F
0,222
E x.s. 0.222 0.059 lg a Cl

    E x.s.

E x.s.
The value of the potential of silver chloride
electrode at different concentrations of water
KCl solution at T= 298 K

Galvanic cells

isometallic
Bimetallic

Galvanic cell (bimetallic)

Anode: Zn - 2e = Zn2+
Cathode: Cu2++2e = Cu
Zn + Cu2+ = Zn2+ + Cu
interface
-Zn|ZnSO4||CuSO4 |Cu +
Eliminated diffusion
potential
solution ZnSO4
solution CuSO4

The measure of the efficiency of the GE element is the EMF or the potential difference of the electrodes:

USE Ekatoda Eanoda;
USE E
0
0
cat.
E
0
if E0Zn 2 / Zn 0.76 B; ECu
0,34,
2
/ Cu
then, E
0
GE
0.34 (0.76) 1.1 B
0,059
E Zn 2 / Zn E
lg a Zn 2
n
0,059
0
ECu2 / Cu ECu2 / Cu
lg a Cu2
n
0
Zn 2 / Zn
E GE
0.059a Cu2
1,1
lg
n
a Zn 2
0
an.

Concentration galvanic cell (isometallic)

Anode: Zn Zn2+(0.1n) +2e
Cathode: Zn2+(1n) +2e Zn
Zn2+(1n) Zn2+(0.1n)
- Zn|Zn2+(0.1n)||Zn2+(1n)|Zn +
p-p ZnSO4 0.1 n (a1)
p-p ZnSO4 1 n (a2)
a1< a 2

E Zn 2 / Zn E
0
Zn 2 / Zn
E Zn 2 / Zn E
0
Zn 2 / Zn
E GE
0,059
lg a Zn 2 (a 2)
n
0,059
lg a Zn 2 (a1)
n
0.059a2
lg
n
a1

Redox potentials

Pt
Fe 2+ (solution) Fe 3+ (solution) + e (Pt pl-ka)
Red Ox + ne
Red - restored form
Ox - oxidized form
Nernst equation:
FeCl2 , FeCl3
E ok. f./ w.f. E
0
OK. f./ w.f.
RT Socid. f-ma
ln
nF
Rest. f-ma
Standard RH potential

Walter Friedrich Hermann Nernst (1864-1941)

RH potential depends on:

temperature
the nature of the oxidizing agent and reducing agent
concentration of oxidized and
restored forms
medium pH

Standard RH potential

EMF GE, composed of redox
systems,
containing
oxidized and reduced forms
concentrations of 1 mol/l and NVE - yes
standard RH potential of the given RH
systems

If we compose the HE from MnO4-/Mn2+ and (Pt),H2|2H+,
then the standard RH potential = +1.51 V.
MnO4- + 8H+ +5e Mn2+ + 4H2O
a(MnO4-)= a(Mn2+)=1 mol/l
a(H+)= 1 mol/l

Under real conditions, the calculation of the OR potential of the MnO4-/Mn2+ system is carried out according to the Nernst equation:

E MnO / Mn 2
4
4
8
RT [MnO][H]
1,51
ln
2
5F
[mn]

The more standard RH
system potential, the more
degree expressed its oxidative
properties under standard conditions.
For example,
MnO4-/Mn2+
Fe3+/Fe2+
Sn4+/Sn2+
E0= 1.51V
E0= 0.77 V
E0= 0.15 V

Criteria for the spontaneous occurrence of OB reactions

G0
G reactions Gprod. Gref. in.
G Auseful Ael.
Ael. q E
qnF
Portable Email
charge
Email work on
electron transfer
Potential difference
between electrodes
The number of electrons passing into
elementary act of the OVR
E Eok la Evla
G nF E
if G 0, then E 0

Example:

3
Co / Co
2
E
0
(ca., c.)
1.84 V
Fe 3 / Fe 2 E (0approx., w.) 0.77 V
So
3
oxidizer
Fe
2
2
reducing agent
HER
E 0, therefore, the reaction proceeds
0
OK.
E
CoFe
3
0
resurrection
1,84 0,77 1,07
random from left to right

Depth of OB reactions

A B C D
K x. R.
[D]
; G 0 RT ln K x. R.
[A][B]
0
G
nF E
RT ln K x. R. nF E nF (Eok0 l i Ev0 l i)
nF (Eok0 l I Ev0 l i)
ln K x. R.
RT
ln K x. R. the more, the greater the difference Eok0 l I Ev0 l I,
a K x. R. evaluates the depth of the flow of chem. reactions

Redox HE

2KI + 2FeCl3  I2 + 2FeCl2 + 2KCl

2KI + 2FeCl3 I2 + 2FeCl2+2KCl
e
Pt
Pt
e
KI
2I- -2e I2
I2 | 2I-
e
FeCl3
Fe3++e Fe2+
Fe3+ | Fe2+
When the circuit is closed in
the left half element goes
oxidation process - I donating electrons
platinum, turn into
I2, resulting plate
conditionally charged
negative.
In the right semi-element
Fe3+ takes electrons from
plates turn into
Fe3+ , plate is charging
conditionally positive.
The system strives
equalize the charges
plates at the expense
electron movement
along the outer circuit.

Ion selective electrodes

glass electrode

R(Na+, Li+) + H+ R(H+) + Na+, Li+
Glass
electrode body
membrane
solution
membrane
solution
Ag AgCl, 0.1 M HCl glass H+, solution
1
2
3
glass = 1+ 2+ 3
Internal solution
0.1 M HCl
1- potential of internal silver chloride
electrode (const)
2- internal surface potential
glass membrane (const)
HSE
3 - potential of the outer surface
glass membrane (variable)
1+ 2 = K
glass \u003d K + 0.059 lg a (H +) or
Electrode glass
(membrane)
glass = K - 0.059 pH

Determination of pH in a laboratory workshop

To measuring
device
The EMF of the presented circuit of Ezepi:
E chains = E x.s. - Eating.
Ecepi \u003d E x.s. – K + 0.059рН
pH
E chains E x.s. To
0,059
E chain const

Oxidation is the process of donating electrons from an atom, molecule, or ion. An atom turns into a positively charged ion: Zn 0 - 2e Zn 2+ a negatively charged ion becomes a neutral atom: 2Cl - -2e Cl 2 0 S 2- -2e S 0 The value of a positively charged ion (atom) increases according to the number of donated electrons: Fe 2 + -1e Fe 3+ Mn +2 -2e Mn +4

Recovery is the process of adding electrons to an atom, molecule or ion. The atom turns into a negatively charged ion S 0 + 2e S 2 Br 0 + e Br The value of a positively charged ion (atom) decreases according to the number of attached electrons: Mn e Mn +2 S e S +4 or it can go into a neutral atom: H + + e H 0 Cu e Cu 0

Reducing agents are atoms, molecules, or ions that donate electrons. They are oxidized during the redox process. Typical reducing agents: metal atoms with large atomic radii (I-A, II-A groups), as well as Fe, Al, Zn simple non-metal substances: hydrogen, carbon, boron; negatively charged ions: Cl, Br, I, S 2, N 3. Fluoride ions F are not a reducing agent. metal ions in the lower s.o.: Fe 2+, Cu +, Mn 2+, Cr 3+; complex ions and molecules containing atoms with an intermediate s.o.: SO 3 2, NO 2; CO, MnO 2, etc.

Oxidizing agents are atoms, molecules, or ions that accept electrons. They are reduced in the process of OVR. Typical oxidizing agents: atoms of non-metals VII-A, VI-A, V-A groups in the composition of simple substances, metal ions in the highest s.d.: Cu 2+, Fe 3+, Ag + ... complex ions and molecules containing atoms with higher and high s.d.: SO 4 2, NO 3, MnO 4, СlО 3, Cr 2 O 7 2-, SO 3, MnO 2, etc.

Sulfur oxidation states: -2.0, +4, +6 H 2 S -2 - reducing agent 2H 2 S + 3O 2 \u003d 2H 2 O + 2SO 2 S 0,S +4 O 2 - oxidizing agent and reducing agent S + O 2 \u003d SO 2 2SO 2 + O 2 \u003d 2SO 3 (reductant) S + 2Na \u003d Na 2 S SO 2 + 2H 2 S \u003d 3S + 2H 2 O (oxidizing agent) H 2 S +6 O 4 - oxidizing agent Cu + 2H 2 SO 4 \u003d CuSO 4 + SO 2 + 2H 2 O

Determination of the oxidation states of atoms of chemical elements С.о. atoms h / e in the composition of a simple being = 0 Algebraic sum of s.d. of all elements in the composition of the ion is equal to the charge of the ion Algebraic sum s.d. of all elements in the composition of a complex substance is 0. K +1 Mn +7 O x + 4 (-2) \u003d 0

Classification of redox reactions Reactions of intermolecular oxidation 2Al 0 + 3Cl 2 0 2Al +3 Cl 3 -1 Reactions of intramolecular oxidation 2KCl +5 O KCl O 2 0 Reactions of disproportionation, dismutation (self-oxidation-self-recovery): 3Cl KOH (gor.) KCl + 5 O 3 + 5KCl -1 + 3H 2 O 2N +4 O 2 + H 2 O HN +3 O 2 + HN +5 O 3

This is useful to know. The oxidation states of the elements in the composition of the salt anion are the same as in the acid, for example: (NH 4) 2 Cr 2 +6 O 7 and H 2 Cr 2 +6 O 7 The oxidation state of oxygen in peroxides is -1 The oxidation state sulfur in some sulfides is -1, for example: FeS 2 Fluorine is the only non-metal that does not have a positive oxidation state in compounds. In compounds NH 3, CH 4, etc., the sign of the electropositive element hydrogen is in second place

Oxidizing properties of concentrated sulfuric acid Sulfur reduction products: H 2 SO 4 + och.akt. metal (Mg, Li, Na…) H 2 S H 2 SO 4 + act. metal (Mn, Fe, Zn…) S H 2 SO 4 + inactive metal (Cu, Ag, Sb…) SO 2 H 2 SO 4 + HBr SO 2 H 2 SO 4 + non-metals (C, P, S…) SO 2 Note: it is often possible to form a mixture of these products in different proportions

Hydrogen peroxide in redox reactions Solution medium Oxidation (H 2 O 2 -reducing agent) Reduction (H 2 O 2 -oxidizing agent) acidic H 2 O 2 -2eO 2 + 2H + (O - 2eO 2 0) H 2 O 2 + 2H + + 2e2H 2 O (O e2O - 2) alkaline H 2 O 2 + 2OH -O 2 + 2H 2 O (O - 2eO 2 0) H 2 O 2 + 2e2OH - (O e2O - 2) neutral H 2 O 2 - 2eO 2 + 2H + (O - 2eO 2 0) H 2 O 2 + 2e2OH - (O e2O - 2)

Nitric acid in redox reactions Nitrogen reduction products: Concentrated HNO 3: N +5 +1e N +4 (NO 2) (Ni, Cu, Ag, Hg; C, S, P, As, Se); passivates Fe, Al, Cr Diluted HNO 3: N +5 +3e N +2 (NO) (Metals in ECHRNM Al …Cu; non-metals S, P, As, Se) Diluted HNO 3: N +5 +4e N +1 (N 2 O) Ca, Mg, Zn Dilute HNO 3: N +5 +5e N 0 (N 2) Very dilute: N e N -3 (NH 4 NO 3) (active metals in ECHRNM up to Al)

Importance of OVR OVR is extremely common. They are associated with metabolic processes in living organisms, respiration, decay, fermentation, photosynthesis. OVR provide the cycle of substances in nature. They can be observed during fuel combustion, corrosion and metal smelting. With their help, alkalis, acids and other valuable chemicals are obtained. OVR underlie the energy conversion of interacting chemical substances into eclectic energy in galvanic cells.

The theme of the project is "Redox Reactions".

creative project name "Someone loses, and someone finds...".

Project coordinator Drobot Svetlana Sergeevna, chemistry teacher, [email protected]

Subject - chemistry.

Eleventh-graders became participants of the project.

The project was carried out from October to December (3 months) in the 11th grade.

Topic "Redox Reactions" runs like a red thread through the entire course of chemistry at school (8, 9 and 11 classes) and is very difficult to understand the processes that occur as a result of these reactions.

Fundamental question: Is the end of the world possible?

On this topic, the following problem questions:

1.Where in the world around us do we meet OVR?
2. What is the difference between exchange reactions and redox reactions?
3. What is the difference between the oxidation state and valence?
4. What are the features of the OVR in organic chemistry?

The problematic questions were designed in such a way as to show in as much detail as possible all the phenomena associated with the redox processes occurring in the world around us and to arouse the interest of the children in the study of these complex chemical processes.

The students carried out research work on the tasks assigned to them. problematic issues. They worked in two directions. Some conducted research considering OVR as a chemical process:

1. Valency and oxidation state.
4. OVR in organic chemistry.
3. What is OVR and what is RIO.
4. Anode + cathode = electrolysis
5. Redox reactions

And others in terms of practical significance process data:
1. In the realm of the red devil.
2. Are you not wearing white yet? Then we go to you!
3. Seven miracles in animate and inanimate nature.
4. This Victory Day...

The presentation "In the realm of the red devil" can be used not only as a research work, but also in chemistry lessons when explaining this topic, because it explains the concept of corrosion, the essence of this process, classification - chemical, electrochemical, mechanochemical; corrosion protection methods. And the material: types of corrosion, you know what .. out of scope curriculum.

The presentation "Are you wearing white yet?…" deals with the use of redox reactions in everyday life. Washing in a scientific way - removing stains of iodine, stains different kind; recommendations for handling products made of natural wool; about the composition of powders and the role of one or another component in washing.

"Seven wonders of animate and inanimate nature". This presentation talks about the seven wonders of animate and inanimate nature - combustion, metal corrosion, explosion, electrolysis, decay, fermentation, photosynthesis. As a result, it was concluded that these seven wonders of animate and inanimate nature relate to redox reactions that surround us and play a huge role in our lives.

"This is the day of victory." The use of redox reactions in warfare.

creative result research work learners becomes an educational site . The site combines all the material on the topic. It also contains a test that allows you to test your knowledge and get an assessment. The advantage of this site is that it is available to any student via the Internet.

Summing up the results of their research work, the students came to the conclusion that the whole world around us can be considered as a giant chemical laboratory, in which chemical reactions occur every second, mainly redox reactions, and as long as redox processes exist in nature, the end of the world is impossible.

In the course of work on the project, didactic material was developed (tests, methods for determining valency, oxidation state; compiling the OVR by the electronic balance method, compiling the OVR by the half-reaction method, the rule for compiling ion exchange reactions).

While working on the project, a large amount of scientific, methodological, popular scientific literature was used.

Internet resources were also used.

Our project will help students to independently understand the difficult issues of this topic, as well as prepare for the exam in chemistry.

The whole world around us can be considered as a gigantic chemical laboratory in which chemical reactions, mainly redox ones, take place every second.

REDOX REACTIONS

1. OVR. OVR classification.
2.Method of electronic balance.
3. Method of half-reactions.

Targets and goals:

To consolidate the ability of students to apply the concept of "oxidation state" in practice.
Summarize and supplement students' knowledge about the basic concepts of the OVR theory.
To improve the ability of students to apply these concepts to the explanation of facts.

Targets and goals:

Introduce students to the essence of the half-reaction method.
To form the ability to express the essence of redox reactions occurring in solutions using the ion-electronic method.

Oxidizing agent and reducing agent

oxidizing agent A reagent that accepts electrons in a redox reaction is called.
restorer is a reagent that donates electrons in a redox reaction.

OXIDATION AND REDUCTION PROCESS

Oxidation called the process of donating electrons by an atom, molecule or ion, which is accompanied by an increase in the degree of oxidation.
Recovery call the process of adding electrons to an atom, molecule or ion, which is accompanied by a decrease in the degree of oxidation.

Rules for determining the function of a compound in redox reactions.

1. If the element exhibits in connection highest degree of oxidation then this connection can be oxidant.
2. If the item exhibits in connection lower oxidation state then this connection can be reducing agent.
3. If the item exhibits in connection intermediate oxidation state then this connection can be like reducer, so and oxidant.
Exercise:
Predict the functions of substances in redox reactions:

The most important oxidizing and reducing agents Basic concepts of the OVR theory

Questions:
1. What is called the recovery process?
2. How does the oxidation state of an element change during reduction?
3. What is called the oxidation process?
4. How does the oxidation state of an element change during oxidation?
5. Define the concept of "reductant".
6. Define the concept of "oxidant".
7. How to predict the function of a substance by the oxidation state of an element?
8. Name the most important reducing agents and oxidizing agents.
9. What reactions are called redox reactions?

chemical reactions chemical reactions

By changing the oxidation state of atoms of elements

Redox

Without changing the oxidation state of the atoms of the elements
These include all ion exchange reactions, as well as many compound reactions.

REDOX REACTIONS

redox
called reactions that are accompanied by a change in the oxidation states of the chemical elements that make up the reagents.

OVR classification

intermolecular oxidation-reduction reactions

intramolecular oxidation-reduction reactions,

reactions of disproportionation, dismutation or self-oxidation-self-recovery

Intermolecular reactions:

Electron donor particles (reductants) - and electron acceptor particles (oxidizers) - are in different substances.
This type includes the majority of OVR.

Intramolecular reactions

An electron donor - a reducing agent - and an electron acceptor - an oxidizing agent - are in the same substance.

Reactions of dismutation, or disproportionation, or self-oxidation-self-healing

Atoms of the same element in a substance simultaneously perform the functions of both electron donors (reducing agents) and electron acceptors (oxidizing agents).
These reactions are possible for substances containing atoms of chemical elements in an intermediate oxidation state.

Compilation of redox reactions

For the preparation of redox reactions, use:
1) electronic balance method
2) Drawing up equations of redox reactions by the half-reaction method, or by the ion-electron method

Compilation of redox reactions electronic balance method

The method is based on comparing the oxidation states of atoms in the initial substances and reaction products and on balancing the number of electrons shifted from the reducing agent to the oxidizing agent.
The method is applied for compiling equations of reactions occurring in any phases. This is the versatility and convenience of the method.
The disadvantage of the method- when expressing the essence of reactions occurring in solutions, the existence of real particles is not reflected.

Algorithmic prescription for compiling equations of redox reactions by the electron balance method

1. Draw up a reaction scheme.
2. Determine the oxidation states of the elements in the reactants and reaction products.
3. Determine whether the reaction is redox or it proceeds without changing the oxidation states of the elements. In the first case, perform all subsequent operations.
4. Underline the elements whose oxidation states change.

5. Determine which element is oxidized (its oxidation state increases) and which element is reduced (its oxidation state decreases) during the reaction.
6. On the left side of the diagram, use arrows to denote the oxidation process (displacement of electrons from an atom of an element) and the reduction process (displacement of electrons to an atom of an element)
7. Determine the reducing agent (the atom of the element from which the electrons are displaced) and the oxidizing agent (the atom of the element to which the electrons are displaced).

Algorithmic prescription for compiling equations of redox reactions by the electron balance method

8. Balance the number of electrons between the oxidizing agent and reducing agent.
9. Determine the coefficients for the oxidizing agent and reducing agent, oxidation and reduction products.
10. Write down the coefficient in front of the formula of the substance that determines the environment of the solution.
11. Check the reaction equation.

Drawing up equations of redox reactions by the half-reaction method, or by the ion-electron method

The method is based on the compilation of ion-electronic equations for the processes of oxidation and reduction, taking into account real-life particles and their subsequent summation into a general equation.
Method applied to express the essence of redox reactions occurring only in solutions.
Advantages of the method.
1. In the electron-ion equations of half-reactions, ions that actually exist in an aqueous solution are written, and not conditional particles. (For example, ions rather than a nitrogen atom with an oxidation state of +3 and a sulfur atom with an oxidation state of +4.)
2. The concept of "oxidation state" is not used.
3. When using this method, you do not need to know all the substances: they are determined when deriving the reaction equation.
4. The role of the environment as an active participant in the entire process is visible.

The main stages of compiling equations of redox reactions ion-electronic method

(on the example of the interaction of zinc with concentrated nitric acid)
1. We write down the ionic scheme of the process, which includes only the reducing agent and its oxidation product, and the oxidizing agent and its reduction product:

Source

USE. CHEMISTRY: Universal reference book / O.V. Meshkova.- M.: EKSMO, 2010.- 368s.

To use the preview of presentations, create an account for yourself ( account) Google and sign in: https://accounts.google.com

Slides captions:

recovery reactions. OVR classification. Lesson objectives: 1. teaching - to systematize students' knowledge of the classification of chemical reactions in the light of electronic theory; - to teach to explain the basic concepts of OVR; - give a classification of OVR 2. developing - develop the ability to observe, draw conclusions; - continue the development of logical thinking, the ability to analyze and compare; 3. educational - to form the scientific outlook of students, improve labor skills; -to cultivate the ability to listen to each other, analyze the situation, improve the culture of interpersonal communication

Basic concepts: redox reactions oxidizer-reductor, processes of oxidation-reduction reactions intermolecular intramolecular disproportionation Equipment: PSCE D. I. Mendeleev

When certain types of chemical bonds are formed, the process of electrons joining an atom or their release occurs, therefore, the formation of common electron pairs or charged particles - cations and anions is possible. Recovery process - the process of accepting electrons by an atom (particle) + n when restoring - s.o. decreases For example +2 Task. Write the process of copper recovery () The oxidation process is the process of giving off electrons by an atom (particle) n As a result, an increase in the degree of oxidation is observed. during oxidation - s.o. rises For example Assignment. Write the process of aluminum oxidation ()

Oxidizing agent and reducing agent. Ability to determine the functions of a substance/particle (oxidizing or reducing) by s.d. element Reductant - a particle, atom, molecule, donating electrons (electron donor). The reducing agent always raises the s.d. Oxidizing agent - a particle, atom, molecule that accepts electrons (electron recipient). The oxidizing agent always lowers the s.d. 1. So if the element in the compound is in the minimum s.d., like sulfur in (-2 is the minimum d.s. of sulfur / group number -8 /), then the compound acts as a reducing agent. For example: ... 2. If in the compound the element is at maximum c. o., like sulfur in - the compound acts as an oxidizing agent For example: H ...

The most important Oxidizing and Reducing Agents Oxidizing agents: K H And also some simple substances Reducing agents H H And also some simple substances Metals, CO, C Task: Find among the proposed compounds oxidizing and reducing agents HN S CuO

All chemical reactions that occur with a change in s.d. elements are called redox.

Intermolecular OVR - electron exchange occurs between different atoms (molecules, ions) - the oxidizing agent and the reducing agent are in different molecules: + = Reactions of intramolecular oxidation and reduction - the oxidizing agent and reducing agent are in the same substance (molecule, particle) = + 2 Reactions disproportionation (dismutation) - reactions in which the same element acts both as an oxidizing agent and as a reducing agent, and as a result of the reaction, compounds are formed that contain the same chemical element in different s.o. K _________________________________________________________________ Task What type of OVR is the reaction: N + + HN

FIXING 2 𝑆+𝑆 = 3S + 2 O Is the OVR reaction? Determine the degree of oxidation of elements Find an oxidizing agent, a reducing agent Determine the type of OVR HOMEWORK 1. item 11, learn 2. write out OVR of all types from the text (two examples each)