Presentation on the topic "electric current in liquids." Physics presentation on the topic "electric current in liquids" Main stages of the lesson

Based on their electrical properties, all liquids can be divided into 2 groups:

LIQUIDS

CONDUCTIVE

NON-CONDUCTIVE

These include distilled water, alcohol, mineral oil

These include solutions (most often aqueous) and melts of salts, acids and bases

Electrolytic dissociation

Electrolytic dissociation is the breakdown of electrolyte molecules into positive and negative ions.

The degree of dissociation is the proportion of molecules in a dissolved substance that have broken up into ions. Depends on:

• temperature

• solution concentration
• electrical properties of the solvent

With increasing temperature, the degree of dissociation increases and, consequently, the concentration of positively and negatively charged ions increases.

Ion recombination

Along with dissociation in the electrolyte, the process of reduction of ions into neutral molecules can simultaneously occur. When ions of different signs meet, they can again combine into neutral molecules - recombine .

Under constant conditions, it is established in the solution dynamic equilibrium, in which the number of molecules that disintegrate into ions per second is equal to the number of pairs of ions that recombine into neutral molecules at the same time.

Ionic conductivity

Charge carriers in aqueous solutions or melts of electrolytes are positively and negatively charged ions.

If a vessel with an electrolyte solution is connected to an electrical circuit, then negative ions will begin to move to the positive electrode - the anode, and positive ions - to the negative - the cathode. As a result, an electric current will be established. Since charge transfer in aqueous solutions or electrolyte melts is carried out by ions, such conductivity is called ionic .

Electrolysis

In ionic conduction, the passage of current is associated with the transfer of matter. At the electrodes, substances that make up the electrolytes are released. At the anode, negatively charged ions give up their extra electrons (in chemistry, this is called an oxidation reaction), and at the cathode, positive ions receive the missing electrons (a reduction reaction). The process of release of a substance at the electrode associated with redox reactions is called electrolysis .

Applications of Electrolysis

Electrolysis is widely used in technology for various purposes. Electrolytically coat the surface of one metal with a thin layer of another ( nickel plating, chrome plating, copper plating etc.). This durable coating protects the surface from corrosion.

If you ensure good peeling of the electrolytic coating from the surface on which the metal is deposited (this is achieved, for example, by applying graphite to the surface), then you can get a copy from the relief surface.

The process of obtaining peelable coatings - electrotype- was developed by the Russian scientist B. S. Jacobi (1801-1874), who in 1836 used this method to make hollow figures for St. Isaac's Cathedral in St. Petersburg.

Another way to use electrolysis is to obtain pure metal from impurities. Electrolysis is used to make printed circuit boards for various digital devices.

• (picture) (picture) (picture)
• Physics. 10th grade: textbook. for general education institutions: basic and profile. levels / G. Ya. Myakishev, B. B. Bukhovtsev, N. N. Sotsky
• http://class-fizika.narod.ru/10_12.htm
• http://www.nado5.ru/e-book/ehlektricheskii-tok-v-zhidkostyakh
• http://rza.org.ua/glossary/image-246.html(picture)
• http://www.electrofaq.com/ETMbook/CONDUCT/CON5A.HTM(picture)
• http://lib.convdocs.org/docs/index-280240.html(picture)

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Purpose of the lesson using the presentation is the formation of the concepts “electrolytes, electrical dissociation, degree of dissociation”; consideration of the phenomenon of electrolysis, derivation of Faraday's law; application of electrolysis in technology.

Lesson topic: “Electric current in liquids.”

Purpose of the lesson:

1. A) Introduce definitions of concepts:

Electrolytes;

Electrical dissociation;

Degree of dissociation.

B) Consider the phenomenon of electrolysis. Faraday's law.

2. Development of observation skills, expansion of horizons.

3. Cultivating interest in the subject being studied.

Equipment: multimedia projector, computer, interactive whiteboard, presentation (Appendix 1).

Lesson type: lesson on learning new material.

Lesson progress

I. Updating knowledge (communication of the topic, purpose and objectives of the lesson). (Slide 2, 3)

II. Learning new material.

A) Questions:

1) What bodies are conductors of electric current?

2) What conductivity do liquid metals have?

In solutions and melts of electrolytes (salts, acids and alkalis), charge transfer under the influence of an electric field is carried out by “+” and “-” ions, which move in opposite directions.

Electrolytes are substances whose solutions and melts have ionic conductivity. (Slide 4)

Question: Why, when dissolved in water, does a solid polar dielectric become a conductor of electric current? (Slide 5)

In order to answer this question, consider the process of dissolving CuCl 2 in water.

(Explanation: In such a crystal, + Cu ions and – Cl ions are located at the sites of a simple cubic lattice.

When a CuCl 2 crystal is immersed in water, the negative OH poles of the water molecules begin to be attracted by Coulomb forces to the positive Cu ions, and the water molecules turn to the negative Cl ions with their positive H pole.

Overcoming the attractive forces between the Cu + and Cl - ions, the electric field of polar water molecules removes the ions from the surface of the crystal)

Conclusion: free carriers appear in the solution - Cu + and Cl -, which are surrounded by polar water molecules.

This phenomenon is called electrical dissociation (from the Latin word - separation). (Slide 6)

Electrical dissociation– splitting of electrolyte molecules into positive and negative ions under the influence of a solvent.

Question: On what parameters does the solubility of a substance depend? (Depending on temperature)

Degree of dissociation– the ratio of the number of molecules dissociated into ions to the total number of molecules of a given substance.

Recombination– the process of combining ions of different signs into neutral molecules.

B) In ionic conduction, the passage of current is associated with the transfer of matter. At the electrodes, substances that make up the electrolytes are released. (Slide 7)

When an external electric field is created in the electrolyte, a directed movement of ions occurs. Copper chloride in an aqueous solution dissociates into copper and chlorine ions.

“+” copper ions (cations) are attracted to the “-” electrode (cathode), and “-” chlorine ions (anions) are attracted to the “+” electrode (anode).

Having reached the cathode, the copper ions are neutralized by the excess electrons that are located at the cathode - as a result, neutral copper atoms are formed, which are deposited on the cathode.

Chlorine ions give up one excess electron at the anode, turning into neutral chlorine atoms, combining in pairs, chlorine atoms form a chlorine molecule, which are released at the anode in the form of gas bubbles.

The process of release of a substance on the electrodes associated with the redox reaction - called electrolysis. (Slide 8)

(The phenomenon of electrolysis was discovered in 1800 by English physicists W. Nichols and A. Carlyle)

What determines the mass of a substance released on the electrodes over a certain time?

Law of electrolysis (Faraday's Law). (Slide 9). (Student message)

Research in the field of electricity, magnetism, magnetooptics, electrochemistry. discovered the phenomenon of electromagnetic induction and established its laws. Experiments on the passage of current through solutions of acids, salts and alkalis were the result of the discovery of the laws of electrolysis (Faraday's laws). He introduced the concept of field and used the term “magnetic field”. For the first time he obtained chlorine in a liquid state, then hydrogen sulfide, carbon dioxide, ammonia and nitrogen dioxide. . Laid the beginning of research into natural rubber. Showed the possibility of photochemical chlorination of ethylene. Introduced the concept of dielectric constant. Faraday's name entered the system of electrical units as a unit of electrical capacity.

Questions? (Slide 10)

1. How to find the mass of a substance released on the electrodes?

2. How to find the mass of one ion?

3. How to find the number of ions?

4. How to find the charge of one ion? (n – valence)

The mass of substance released on the electrode during the passage of an electric current is directly proportional to the current strength and time. (This statement was obtained in 1833 by the English physicist Michael Faraday and is called Faraday's law).

K – electrochemical equivalent of the substance (depends on the molar mass of the substance “M” and valence “n”)

Phys. the meaning of k is numerically equal to the mass of the substance released on the electrode when a charge of 1 C passes through the electrolyte.

N a *e=F – Faraday constant. (Slide 12)

The physical meaning of F is numerically equal to the charge that must be passed through the electrolyte solution in order to release 1 mole of a monovalent substance on the electrode.

IN) Application of electrolysis in technology (student message). (Slide 13)

1. Electroplating is a decorative or anti-corrosion coating of metal products with a thin layer of another metal (nickel plating, chrome plating, copper plating, gold plating).
2. Electroplating is the electrolytic production of metal copies and relief objects. This method was used to make figures for St. Isaac's Cathedral in St. Petersburg.
3. Electrometallurgy - production of pure metals by electrolysis of molten ores (Al, Na, Mg, Be).
4. Metal refining - purification of metals from impurities. (Slide 14–17)

G) Lesson summary behavior.

1. What substances are called electrolytes?

2. Define:

electrical dissociation;

degree of dissociation;

recombination.

3. What process is called electrolysis? Who opened it and when?

4. Formulate Faraday's law?

5. Physical meaning of the electrochemical equivalent of a substance and Faraday’s constant.

Homework: §§ 122-123, ex. 20 (4, 5). (Slide 18)

References

1. Educational electronic publication “Interactive physics course for grades 7-11”, “Physicon”, 2004.

2. “Open Physics 1.1”, LLC “Physikon”, 1996-2001, edited by MIPT professor S.M. Cosella.

3. “Library of electronic visual aids. Physics 7-11 grades”, State Institution RC EMTO, “Cyril and Methodius”, 2003

As is known, chemically pure (distilled)
water is a poor conductor. However, when
dissolving various substances in water (acids,
alkalis, salts, etc.) the solution becomes a conductor,
due to the breakdown of substance molecules into ions. This is a phenomenon
is called electrolytic dissociation, and itself
solution with an electrolyte capable of conducting current.

Electrolysis

ELECTROLYSIS
Electrolysis is a physical and chemical process consisting of the separation
on the electrodes of constituents of dissolved substances or other
substances resulting from secondary reactions at the electrodes,
which occurs when an electric current passes through
solution or molten electrolyte.

Michael Faraday.

Michael Faraday is an English experimental physicist and chemist. Member of London
Royal Society (1824) and many
other scientific organizations, including
foreign honorary member of the St. Petersburg
Academy of Sciences (1830).
Discovered electromagnetic induction
underlying modern
industrial production
electricity and its many applications.
Created the first model of an electric motor.
Among his other discoveries is the first
transformer, chemical action
current, laws of electrolysis, action
magnetic field to light, diamagnetism.
First predicted electromagnetic
waves. Faraday introduced into scientific use
terms ion, cathode, anode,
electrolyte, dielectric, diamagnetism, steam
magnetism, etc. Also published in 1836
The laws of electrolysis, named in
afterwards in his honor.

Faraday's 1st Law of Electrolysis-

Faraday's 1st Law of Electrolysis
The mass of the substance released at any of the electrodes is directly
proportional to the charge passing through the electrolyte
Electrochemical equivalent of a substance - tabular value.

Faraday's 2nd Law of Electrolysis-

Faraday's 2nd Law of Electrolysis
Electrochemical equivalents of various substances are referred to as
their chemical equivalents.
The flow of current in liquids is accompanied by the release
warmth. In this case, the Joule-Lenz law is fulfilled.

Electrical dissociation:

Dissociation into ions in solutions occurs due to interaction
solute with solvent; according to spectroscopic data
methods, this interaction is largely chemical
character. Along with the solvating ability of solvent molecules
also plays a certain role in electrolytic dissociation
macroscopic property of a solvent - its dielectric
permeability.

Slide 2

Slide 3

Lesson methods Problem-dialogical with the use of information and communication technologies, elements of brainstorming, demonstration experiments and preparation of a reference summary

Slide 4

Mathematics - plotting graphs, converting formulas, calculations. Intersubject communication Chemistry - electrolytic dissociation, electrolysis

Slide 5

Main stages of the lesson

Organizational moment Updating knowledge. Brainstorming Motivation. Demonstration experience Problem statement Provocative dialogue. Finding and solving the problem Demonstration experiment. Integration into the field of chemistry. Leading dialogue Systematization and generalization of knowledge Searching for information on the Internet Consolidating knowledge Homework

Slide 6

Answer the questions

What groups are all substances divided into according to the conductivity of electric current? Give examples of the best conductors of electric current. What particles cause current in metals? Will the electrical conductivity of a metal change if it is heated? Will the electrical conductivity of a metal change if it is melted? What liquids do you know that conduct electricity, other than molten metals?

Slide 7

Does water conduct electricity?

Slide 8

Questions for research How does the resistance of the electrolyte depend on temperature, the geometric parameters of the electrolyte? Why does pure water not conduct, but a salt solution conducts electric current? What causes the electric current in a salt solution?

Slide 9

Liquids that conduct electricity well Electrolytes Salt solutions Alkali solutions Acid solutions

Slide 10

When oppositely charged electrodes are lowered into a solution of copper sulfate, a directed movement of ions occurs. Copper sulfate in an aqueous solution dissociates into copper ions and an acidic residue.

Slide 11

Slide 12

The process of releasing substances that make up an electrolyte on electrodes when an electric current flows through its solution (or melt) is called electrolysis. Electrolysis has wide technical applications. Where is electrolysis used? You need to prepare an answer to this question using the Internet.

Slide 13

What determines the mass of the substance deposited on the electrode?

Electrolytic dissociation is the splitting of molecules into positive and negative ions under the action of a solvent. When ions of different signs come together, their recombination (combination) into one molecule is possible

Slide 14

Michael Faraday - great English scientist, creator of the general doctrine of electromagnetic phenomena

Michael Faraday experimentally established the law of electrolysis in 1833. He introduced the now generally accepted terms: electrode, cathode, anode, electrolyte, electrolysis.

Slide 15

Complete test tasks

I. Indicate the incorrect answer 1. Liquids can be dielectrics, conductors, semiconductors. 2. All liquids are electrolytes. 3. Solutions of salts, alkalis, acids and molten salts that have electrical conductivity are called electrolytes. II. Electrolytic dissociation is called... III. Recombination is called... IV. Electrolysis is called... 1. the process of releasing substances that make up the electrolyte on the electrodes. 2. combining ions of different signs into neutral molecules. 3. the formation of positive and negative ions when substances are dissolved in a liquid. V. With increasing temperature of the electrolyte, its electrical conductivity... 1. increases. 2. decreases. 3. does not change.

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