What creates current in liquids. Electric current in liquids: its origin, quantitative and qualitative characteristics

Absolutely everyone knows that liquids can perfectly conduct electrical energy. And it is also a well-known fact that all conductors are divided into several subgroups according to their type. We propose to consider in our article how an electric current is carried out in liquids, metals and other semiconductors, as well as the laws of electrolysis and its types.

Theory of electrolysis

To make it easier to understand what in question, we propose to start with a theory, electricity, if we consider an electric charge as a kind of liquid, has been known for over 200 years. Charges are made up of individual electrons, but those are so small that any large charge behaves like a continuous flow, a liquid.

Like solid-type bodies, liquid conductors can be of three types:

• semiconductors (selenium, sulfides and others);
• dielectrics ( alkaline solutions, salts and acids);
• conductors (say, in a plasma).

The process in which electrolytes dissolve and ions disintegrate under the influence of an electric molar field is called dissociation. In turn, the proportion of molecules that have decayed into ions, or decayed ions in a solute, depends entirely on physical properties and temperatures in various conductors and melts. Be sure to remember that ions can recombine or recombine. If the conditions do not change, then the number of decayed ions and united will be equally proportional.

In electrolytes, ions conduct energy, because. they can be both positively charged particles and negatively. During the connection of the liquid (or rather, the vessel with the liquid to the mains), the movement of particles to opposite charges will begin (positive ions will begin to be attracted to the cathodes, and negative ions to the anodes). In this case, energy is transported directly by ions, so this type of conductivity is called ionic.

During this type of conduction, current is carried by ions and substances are released at the electrodes that are constituents of electrolytes. Chemically speaking, oxidation and reduction occur. Thus, electric current in gases and liquids is transported by means of electrolysis.

The laws of physics and current in liquids

Electricity in our homes and appliances is usually not transmitted in metal wires. In a metal, electrons can move from atom to atom and thus carry a negative charge.

Like liquids, they are driven in the form of electrical voltage, known as voltage, measured in units of volts, after the Italian scientist Alessandro Volta.

Video: Electricity in liquids: a complete theory

Also, electric current flows from high voltage to low voltage and is measured in units known as amperes, named after André-Marie Ampère. And according to the theory and formula, if you increase the voltage, then its strength will also increase proportionally. This relationship is known as Ohm's law. As an example, the virtual current characteristic is below.

Figure: current versus voltage

Ohm's law (with additional details on wire length and thickness) is typically one of the first things taught in physics classes, and many students and teachers therefore view electric current in gases and liquids as a basic law in physics.

In order to see with your own eyes the movement of charges, you need to prepare a flask with salt water, flat rectangular electrodes and power sources, you will also need an ammeter installation, with the help of which energy will be conducted from the power supply to the electrodes.

Pattern: Current and salt

The plates that act as conductors must be lowered into the liquid and the voltage turned on. After that, the chaotic movement of particles will begin, but after the appearance magnetic field between conductors, this process will be streamlined.

As soon as the ions begin to change charges and combine, the anodes become cathodes, and the cathodes become anodes. But here you need to take into account the electrical resistance. Of course, the theoretical curve plays an important role, but the main influence is the temperature and the level of dissociation (depending on which carriers are chosen), as well as the choice of alternating current or direct current. Completing this experimental study, you can notice that a thin layer of salt has formed on solid bodies (metal plates).

Electrolysis and vacuum

Electric current in vacuum and liquids is a rather complicated issue. The fact is that in such media there are no charges in the bodies, which means that it is a dielectric. In other words, our goal is to create conditions so that an atom of an electron can start its movement.

To do this, you need to use a modular device, conductors and metal plates, and then proceed as in the method above.

Conductors and vacuum Current characteristic in vacuum

Application of electrolysis

This process is applied in almost all areas of life. Even the most elementary work sometimes requires the intervention of an electric current in liquids, say,

With the help of this simple process, solid bodies are coated with the thinnest layer of any metal, for example, nickel plating or chromium plating. this is one of possible ways fight against corrosion processes. Similar technologies are used in the manufacture of transformers, meters and other electrical appliances.

We hope that our rationale has answered all the questions that arise when studying the phenomenon of electric current in liquids. If you need better answers, then we advise you to visit the forum of electricians, where you will be happy to consult for free.

>>Physics: Electric current in liquids

Liquids, like solid bodies, can be dielectrics, conductors and semiconductors. Dielectrics include distilled water, conductors include solutions and melts of electrolytes: acids, alkalis and salts. Liquid semiconductors are molten selenium, sulfide melts, etc.
electrolytic dissociation. When electrolytes are dissolved under the influence electric field polar water molecules, electrolyte molecules break down into ions. This process is called electrolytic dissociation.
Degree of dissociation, i.e., the proportion of molecules in the solute that have decayed into ions depends on the temperature, concentration of the solution, and electrical properties solvent. With increasing temperature, the degree of dissociation increases and, consequently, the concentration of positively and negatively charged ions increases.
Ions of different signs, upon meeting, can again unite into neutral molecules - recombine. Under constant conditions, a dynamic equilibrium is established in the solution, at which the number of molecules that decay into ions per second is equal to the number of pairs of ions that recombine into neutral molecules in the same time.
Ionic conduction. Charge carriers in aqueous solutions or electrolyte melts are positively and negatively charged ions.
If a vessel with an electrolyte solution is included in an electrical circuit, then negative ions will begin to move towards the positive electrode - the anode, and positive - towards the negative - cathode. As a result, an electric current will be established. Since the charge transfer in aqueous solutions or electrolyte melts is carried out by ions, such conductivity is called ionic.
Liquids can also have electronic conductivity. Such conductivity is possessed, for example, by liquid metals.
Electrolysis. With ionic conductivity, the passage of current is associated with the transfer of matter. On the electrodes, substances that make up electrolytes are released. At the anode, negative ions donate their extra electrons (in chemistry, this is called an oxidative reaction), and at the cathode, positive ions receive the missing electrons (reduction reaction). The process of release of a substance at the electrode, associated with redox reactions, is called electrolysis.
Application of electrolysis. Electrolysis is widely used in engineering for various purposes. Electrolytically cover 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 good peeling of the electrolytic coating is ensured from the surface on which the metal is deposited (this is achieved, for example, by applying graphite to the surface), then a copy can be obtained from the relief surface.
In the printing industry, such copies (stereotypes) are obtained from matrices (an imprint of a set on a plastic material), for which a thick layer of iron or another substance is deposited on the matrices. This allows you to reproduce the set in the desired number of copies. If earlier the circulation of a book was limited by the number of prints that can be obtained from one set (when printing, the set is gradually erased), now the use of stereotypes can significantly increase the circulation. True, at present, with the help of electrolysis, stereotypes are obtained only for books of high quality printing.
The process of obtaining peelable coatings - electrotype- was developed by the Russian scientist B. S. Jacobi (1801-1874), who in 1836 applied this method to make hollow figures for St. Isaac's Cathedral in St. Petersburg.
Electrolysis removes impurities from metals. Thus, crude copper obtained from the ore is cast in the form of thick sheets, which are then placed in a bath as anodes. During electrolysis, the anode copper dissolves, impurities containing valuable and rare metals fall to the bottom, and pure copper settles on the cathode.
Aluminum is obtained from molten bauxite by electrolysis. It was this method of obtaining aluminum that made it cheap and, along with iron, the most common in technology and everyday life.
With the help of electrolysis, electronic circuit boards are obtained, which serve as the basis for all electronic products. A thin copper plate is glued onto the dielectric, on which a complex pattern of connecting wires is applied with a special paint. Then the plate is placed in an electrolyte, where the areas of the copper layer that are not covered with paint are etched. After that, the paint is washed off and the details of the microcircuit appear on the board.
In solutions and melts of electrolytes, free electric charges appear due to the decay of neutral molecules into ions. The movement of ions in the field means the transfer of matter. This process is widely used in practice (electrolysis).

???
1. What is called electrolytic dissociation?
2. Why does a substance transfer occur when a current passes through an electrolyte solution, but does not transfer a substance when passing through a metal conductor?
3. What is the similarity and difference between the intrinsic conductivity of semiconductors and electrolyte solutions?

G.Ya.Myakishev, B.B.Bukhovtsev, N.N.Sotsky, Physics Grade 10

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Liquids according to the degree of electrical conductivity are divided into:
dielectrics (distilled water),
conductors (electrolytes),
semiconductors (molten selenium).

Electrolyte

It is a conductive liquid (solutions of acids, alkalis, salts and molten salts).

Electrolytic dissociation
(disconnection)

During dissolution, as a result of thermal motion, collisions of solvent molecules and neutral electrolyte molecules occur.
Molecules break up into positive and negative ions.

The phenomenon of electrolysis

- accompanies the passage of electric current through the liquid;
- this is the release on the electrodes of substances included in electrolytes;
Positively charged anions tend to the negative cathode under the action of an electric field, and negatively charged cations tend to the positive anode.
At the anode, negative ions donate extra electrons ( oxidative reaction)
At the cathode, the positive ions gain the missing electrons (reduction reaction).

law of electrolysis

1833 - Faraday

The law of electrolysis determines the mass of the substance released on the electrode during electrolysis during the passage of an electric current.

k is the electrochemical equivalent of a substance, numerically equal to the mass of the substance released on the electrode when a charge of 1 C passes through the electrolyte.
Knowing the mass of the released substance, it is possible to determine the charge of the electron.

For example, dissolving copper sulfate in water.

Conductivity of electrolytes, the ability of electrolytes to conduct an electric current when an electric voltage is applied. Current carriers are positively and negatively charged ions - cations and anions that exist in solution due to electrolytic dissociation. The ionic electrical conductivity of electrolytes, in contrast to the electronic conductivity characteristic of metals, is accompanied by the transfer of matter to the electrodes with the formation of new ones near them. chemical compounds. The total (total) conductivity consists of the conductivity of cations and anions, which, under the action of an external electric field, move in opposite directions. The share of the total amount of electricity carried by individual ions is called the transfer numbers, the sum of which for all types of ions involved in the transfer is equal to one.

Semiconductor

Monocrystalline silicon is the most widely used semiconductor material in industry today.

Semiconductor- a material that, in its specific conductivity, occupies an intermediate position between conductors and dielectrics and differs from conductors in a strong dependence of specific conductivity on the concentration of impurities, temperature and exposure to various types of radiation. The main property of a semiconductor is an increase in electrical conductivity with increasing temperature.

Semiconductors are substances whose band gap is on the order of a few electron volts (eV). For example, a diamond can be classified as wide gap semiconductors, and indium arsenide - to narrow-gap. Many semiconductors are chemical elements(germanium, silicon, selenium, tellurium, arsenic and others), a huge number of alloys and chemical compounds (gallium arsenide, etc.). Almost all inorganic substances the world around us - semiconductors. The most common semiconductor in nature is silicon, which makes up almost 30% of the earth's crust.

Depending on whether the impurity atom donates or captures an electron, impurity atoms are called donor or acceptor atoms. The nature of the impurity may vary depending on which atom crystal lattice it replaces in which crystallographic plane it is embedded.

The conductivity of semiconductors is highly dependent on temperature. near temperature absolute zero semiconductors have the properties of dielectrics.

Mechanism of electrical conduction[edit | edit wiki text]

Semiconductors are characterized by both the properties of conductors and dielectrics. In semiconductor crystals, atoms establish covalent bonds (that is, one electron in a silicon crystal, like diamond, is bonded by two atoms), electrons need a level of internal energy to be released from an atom (1.76 10 −19 J versus 11.2 10 −19 J, which characterizes the difference between semiconductors and dielectrics). This energy appears in them with an increase in temperature (for example, at room temperature, the energy level of the thermal motion of atoms is 0.4 10 −19 J), and individual electrons receive energy to detach from the nucleus. As the temperature rises, the number of free electrons and holes increases; therefore, in a semiconductor that does not contain impurities, the electrical resistivity decreases. It is conventionally accepted to consider as semiconductors elements with an electron binding energy of less than 1.5-2 eV. The electron-hole mechanism of conduction manifests itself in intrinsic (that is, without impurities) semiconductors. It is called intrinsic electrical conductivity of semiconductors.

Hole[edit | edit wiki text]

Main article:Hole

When the bond between the electron and the nucleus is broken, free space appears in electron shell atom. This causes the transfer of an electron from another atom to an atom with free space. The atom, from which the electron has passed, enters another electron from another atom, etc. This process is determined by the covalent bonds of atoms. Thus, there is a movement of a positive charge without moving the atom itself. This conditional positive charge is called a hole.

A magnetic field

A magnetic field- a force field acting on moving electric charges and on bodies with a magnetic moment, regardless of the state of their movement; magnetic component of the electromagnetic field.

The magnetic field can be created by the current of charged particles and/or the magnetic moments of electrons in atoms (and the magnetic moments of other particles, which usually manifests itself to a much lesser extent) (permanent magnets).

In addition, it arises as a result of a change in time of the electric field.

The main power characteristic of the magnetic field is magnetic induction vector (magnetic field induction vector) . From a mathematical point of view - vector field that defines and specifies the physical concept of a magnetic field. Often the vector of magnetic induction is called simply a magnetic field for brevity (although this is probably not the most strict use of the term).

Another fundamental characteristic of the magnetic field (alternative magnetic induction and closely related to it, almost equal to it in physical meaning) is an vector potential .

Sources of the magnetic field[edit | edit wiki text]

The magnetic field is created (generated) by the current of charged particles, or by a time-varying electric field, or by the intrinsic magnetic moments of the particles (the latter, for the sake of uniformity of the picture, can be formally reduced to electric currents

The origin of an electric current (the movement of electric charges) through a solution differs significantly from the movement of electric charges along a metal conductor.

The difference, first of all, is that charge carriers in solutions are not electrons, but ions, i.e. atoms or molecules themselves that have lost or gained one or more electrons.

Naturally, this movement, one way or another, is accompanied by a change in the properties of the substance itself.

Consider an electrical circuit, the element of which is a vessel with a solution of common salt and with electrodes of any shape inserted into it from a plate. When connected to a power source, a current appears in the circuit, which is the movement of heavy charged particles - ions in the solution. The appearance of ions already means the possibility of chemical decomposition of the solution into two main elements - Na and Cl. Sodium that has lost an electron is a positively charged ion moving towards an electrode that is connected to the negative pole of a power source, electrical circuit. Chlorine, having “usurped” an electron, is a negative ion.

Negative chlorine ions move towards the electrode, which is connected to the positive pole of the electric power supply. chains.

The formation of positive and negative ions occurs due to the spontaneous decomposition of a sodium chloride molecule in an aqueous solution ( electrolytic dissociation). The movement of ions is due to the voltage applied to the electrodes dipped into the solution. Having reached the electrodes, the ions take or donate electrons, forming Cl and Na molecules, respectively. Similar phenomena are observed in solutions of many other substances. The molecules of these substances, like the molecules of table salt, consist of oppositely charged ions, into which they decompose in solutions. The number of decayed molecules, more precisely, the number of ions, characterizes the electrical resistance of the solution.

We emphasize once again that the origin of an electric current along a circuit, the element of which is a solution, causes the substance of this element of the electric circuit to move, and, consequently, its change chemical properties, while when an electric current passes through a metal conductor, no changes occur in the conductor.

What determines the amount of substance released during electrolysis at the electrodes? Faraday was the first to answer this question. Faraday showed experimentally that the mass of the released substance is related to the strength of the current and the time of its flow t by the relation (Faraday's law):

The mass of a substance released during the electrolysis of a substance is directly proportional to the amount of electricity passed through the electrolyte and does not depend on other reasons, except for the type of substance.

This pattern can be verified in the following experiments. Let's pour the same electrolyte into several baths, but with different concentrations. Let us put electrodes with different areas into the baths and place them in the baths at different distances. We connect all the baths in series and pass current through them. Then through each of the baths, obviously, the same amount of electricity will pass. Weighing the cathodes before and after the experiment, we find that the same amount of substance was released on all cathodes. By connecting all the baths in parallel and passing a current through them, one can be convinced that the amount of substance released on the cathodes is directly proportional to the amount of electricity that has passed through each of them. Finally, by connecting the baths with different electrolytes in series, it is easy to establish that the amount of the released substance depends on the type of this substance.

The value characterizing the dependence of the amount of a substance released during electrolysis on its kind is called the electrochemical equivalent and is denoted by the letter k.

The mass of the substance released during electrolysis is the total mass of all ions discharged at the electrode. By subjecting various salts to electrolysis, one can experimentally determine the amount of electricity that must pass through the electrolyte in order to release one kilogram - the equivalent of a given substance. Faraday was the first to make such experiments. He found that the release of one kilogram - the equivalent of any substance during electrolysis requires the same amount of electricity, equal to 9.65 107 k.

The amount of electricity required to release a kilogram - the equivalent of a substance during electrolysis, is called the Faraday number and is denoted by the letter F:

F = 9.65 107 k.

In the electrolyte, the ion is surrounded by solvent molecules (water) that have significant dipole moments. Interacting with an ion, dipole molecules turn towards it with their ends, which have a charge whose sign is opposite to the charge of the ion, so the orderly movement of the ion in an electric field is difficult, and the mobility of ions is much inferior to the mobility of conduction electrons in the metal. Since the concentration of ions is usually not high compared to the concentration of electrons in a metal, the electrical conductivity of electrolytes is always significantly less than the electrical conductivity of metals.

Due to the strong heating by the current in electrolytes, only insignificant current densities are achievable, i.e. small electric field strengths. With an increase in the temperature of the electrolyte, the ordered orientation of the dipoles of the solvent deteriorates under the influence of the increased random motion of the molecules, so the dipole shell is partially destroyed, the mobility of the ions and the conductivity of the solution increase. The dependence of electrical conductivity on concentration at a constant temperature is complex. If dissolution is possible in any proportion, then at a certain concentration, the electrical conductivity has a maximum. The reason for this is this: the probability of decay of molecules into ions is proportional to the number of solvent molecules and the number of solute molecules per unit volume. But the reverse process is also possible: (recombination of ions into molecules), the probability of which is proportional to the square of the number of pairs of ions. Finally, electrical conductivity is proportional to the number of pairs of ions per unit volume. Therefore, at low concentrations, dissociation is complete, but total number few ions. At very high concentrations, dissociation is weak and the number of ions is also small. If the solubility of a substance is limited, then usually a maximum of electrical conductivity is not observed. When frozen, the viscosity of an aqueous solution increases sharply, the mobility of ions decreases sharply, and the specific electrical conductivity drops a thousand times. When liquid metals solidify, the electron mobility and electrical conductivity remain almost unchanged.

Electrolysis is widely used in various electrochemical industries. The most important of them: electrolytic production of metals from aqueous solutions their salts and from their molten salts; electrolysis of chloride salts; electrolytic oxidation and reduction; hydrogen production by electrolysis; electroplating; electrotype; electropolishing. By refining, a pure metal is obtained, freed from impurities. Electroplating is the coating of metal objects with another layer of metal. Electroplating - obtaining metal copies from relief images of any surfaces. Electropolishing - leveling of metal surfaces.

Liquids that are conductors include melts and electrolyte solutions, i.e. salts, acids and alkalis.

When electrolytes dissolve in water, their molecules break down into ions - electrolytic dissociation. The degree of dissociation, i.e. the proportion of molecules in the solute that have decomposed into ions depends on the temperature, the concentration of the solution, and the electrical properties of the solvent. With increasing temperature, the degree of dissociation increases and, consequently, the concentration of positively and negatively charged ions increases. Ions of different signs, upon meeting, can again unite into neutral molecules. This process is called recombination. Under constant conditions, a dynamic equilibrium is established in the solution, at which the number of molecules that decay into ions per second is equal to the number of pairs of ions that recombine into neutral molecules in the same time.

Thus, free charge carriers in conductive liquids are positive and negative ions. If electrodes connected to a current source are placed in a liquid, then these ions will begin to move. One of the electrodes is connected to the negative pole of the current source - it is called the cathode - the other is connected to the positive - the anode. When connected to a current source, ions in an electrolyte solution, negative ions begin to move towards the positive electrode (anode), and positive ions, respectively, towards the negative (cathode). That is, an electric current is established. Such conductivity in liquids is called ionic, since ions are charge carriers.

When current passes through the electrolyte solution on the electrodes, a substance is released associated with redox reactions. At the anode, negatively charged ions donate their extra electrons (oxidative reaction), and at the cathode, positive ions accept the missing electrons (reduction reaction). This process is called electrolysis.

During electrolysis, a substance is released at the electrodes. The dependence of the mass of the released substance m on the strength of the current, the time of passage of the current and the substance itself was established by M. Faraday. This law can be obtained theoretically. So, the mass of the released substance is equal to the product of the mass of one ion m i by the number of ions N i that reached the electrode during the time Dt. The mass of the ion according to the formula for the amount of substance is m i \u003d M / N a, where M is molar mass substances, N a is the Avogadro constant. The number of ions that have reached the electrode is N i =Dq/qi, where Dq is the charge that passed through the electrolyte during the time Dt (Dq=I*Dt), qi is the charge of the ion, which is determined by the valency of the atom (qi = n*e, where n is the valency of the atom, e is the elementary charge). Substituting these formulas, we obtain that m=M/(neN a)*IDt. If we denote by k (proportionality factor) =M/(neN a), then we have m=kIDt. This is the mathematical notation of Faraday's first law, one of the laws of electrolysis. The mass of the substance released on the electrode during the time Dt during the passage of an electric current is proportional to the current strength and this time interval. The value of k is called the electrochemical equivalent of a given substance, which is numerically equal to the mass of the substance released on the electrodes during the transfer of a charge of 1 C by ions. [k]= 1 kg/C. k = M/(neN a) = 1/F*M/n , where F is Faraday's constant. F \u003d eN a \u003d 9.65 * 10 4 C / mol. The derived formula k=(1/F)*(M/n) is Faraday's second law.

Electrolysis is widely used in engineering for various purposes, for example, the surface of one metal is covered with a thin layer of another (nickel plating, chromium plating, copper plating, etc.). If good peeling of the electrolytic coating from the surface is ensured, a copy of the surface topography can be obtained. This process is called electroplating. Also, using electrolysis, metals are purified from impurities, for example, thick sheets of unrefined copper obtained from ore are placed in a bath as an anode. During electrolysis, copper dissolves, impurities fall to the bottom, and pure copper settles on the cathode. With the help of electrolysis, electronic circuit boards are also obtained. A thin, complex pattern of connecting wires is glued onto the dielectric, then the plate is placed in an electrolyte, where the unpainted areas of the copper layer are etched away. After that, the paint is washed off and the details of the microcircuit appear on the board.