Everyone is familiar with the definition of electric current. It is represented as a directed motion of charged particles. Such movement in different environments has fundamental differences. As a basic example of this phenomenon, one can imagine the flow and propagation of electric current in liquids. Such phenomena are characterized by different properties and are seriously different from the ordered movement of charged particles, which occurs under normal conditions not under the influence of various liquids.

Picture 1. Electricity in liquids. Author24 - online exchange of student papers

Formation of electric current in liquids

Despite the fact that the process of conduction of electric current is carried out by means of metal devices (conductors), the current in liquids depends on the movement of charged ions that have acquired or lost such atoms and molecules for some specific reason. An indicator of such a movement is a change in the properties of a certain substance, where the ions pass. Thus, it is necessary to rely on the basic definition of electric current in order to form a specific concept of the formation of current in various liquids. It is determined that the decomposition of negatively charged ions contributes to the movement to the region of the current source with positive values. Positively charged ions in such processes will move in the opposite direction - to a negative current source.

Liquid conductors are divided into three main types:

• semiconductors;
• dielectrics;
• conductors.

Definition 1

Electrolytic dissociation - the process of decomposition of molecules certain solution into negative and positive charged ions.

It can be established that an electric current in liquids can occur after a change in the composition and chemical properties of the liquids used. This completely contradicts the theory of the propagation of electric current in other ways when using a conventional metal conductor.

Faraday's experiments and electrolysis

The flow of electric current in liquids is a product of the movement of charged ions. The problems associated with the emergence and propagation of electric current in liquids led to the study of the famous scientist Michael Faraday. He, with the help of numerous practical research was able to find evidence that the mass of a substance released during electrolysis depends on the amount of time and electricity. In this case, the time during which the experiments were carried out is important.

The scientist was also able to find out that in the process of electrolysis, when a certain amount of a substance is released, the same amount is needed. electric charges. This number was accurately determined and fixed in constant value, which is called the Faraday number.

In liquids, electric current has different propagation conditions. It interacts with water molecules. They significantly impede all movement of ions, which was not observed in experiments using a conventional metal conductor. It follows from this that the generation of current at electrolytic reactions won't be that big. However, as the temperature of the solution increases, the conductivity gradually increases. This means that the voltage of the electric current is increasing. Also in the process of electrolysis, it was noticed that the probability of a certain molecule decaying into negative or positive ion charges increases due to a large number molecules of the substance or solvent used. When the solution is saturated with ions in excess of a certain norm, the reverse process occurs. The conductivity of the solution begins to decrease again.

Currently, the electrolysis process has found its application in many fields and fields of science and in production. Industrial enterprises use it in the production or processing of metal. Electrochemical reactions are involved in:

• salt electrolysis;
• electroplating;
• surface polishing;
• other redox processes.

Electric current in vacuum and liquids

The propagation of electric current in liquids and other media is a rather complex process that has its own characteristics, features and properties. The fact is that in such media there are completely no charges in the bodies, therefore they are usually called dielectrics. The main goal of the research was to create such conditions under which atoms and molecules could begin their movement and the process of generating an electric current began. For this, it is customary to use special mechanisms or devices. The main element of such modular devices are conductors in the form of metal plates.

To determine the main parameters of the current, it is necessary to use known theories and formulas. The most common is Ohm's law. It acts as a universal ampere characteristic, where the principle of current-voltage dependence is implemented. Recall that voltage is measured in units of amperes.

For experiments with water and salt, it is necessary to prepare a vessel with salt water. This will give a practical and visual representation of the processes that occur when an electric current is generated in liquids. Also, the installation should contain rectangular electrodes and power supplies. For full-scale preparation for experiments, you need to have an ampere installation. It will help conduct energy from the power supply to the electrodes.

Metal plates will act as conductors. They are dipped into the liquid used, and then the voltage is connected. The movement of particles begins immediately. It runs randomly. When magnetic field between the conductors, all the processes of particle movement are ordered.

The ions begin to change charges and combine. Thus cathodes become anodes and anodes become cathodes. In this process, there are also several other important factors to consider:

• dissociation level;
• temperature;
• electrical resistance;
• use of alternating or direct current.

At the end of the experiment, a layer of salt is formed on the plates.

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 electric circuit, the element of which is a vessel with a solution table 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 through a circuit whose element is a solution causes the substance of this element of the electric circuit to move, and, consequently, a change in its chemical properties, while when an electric current passes through a metal conductor, there are no changes in the conductor happening.

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 checked for 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 tensions electric field. 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 as follows: the probability of decay of molecules into ions is proportional to the number of solvent molecules and the number of molecules solute in a unit of 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 the total number of ions is small. 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. During freezing, 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 are: electrolytic production of metals from aqueous solutions of 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. Galvanoplasty - obtaining metal copies from relief images of any surfaces. Electropolishing - leveling of metal surfaces.

Almost every person knows the definition of electric current as However, the whole point is that its origin and movement in various media are quite different from each other. In particular, electric current in liquids has somewhat different properties than It's about about the same metal conductors.

The main difference is that the current in liquids is the movement of charged ions, that is, atoms or even molecules that have lost or gained electrons for some reason. At the same time, one of the indicators of this movement is a change in the properties of the substance through which these ions pass. Based on the definition of electric current, we can assume that during decomposition, negatively charged ions will move towards positive and positive, on the contrary, towards negative.

The process of decomposition of solution molecules into positive and negative charged ions is called in science electrolytic dissociation. Thus, an electric current in liquids arises due to the fact that, in contrast to the same metallic conductor, the composition and Chemical properties these liquids, resulting in the process of movement of charged ions.

The electric current in liquids, its origin, quantitative and qualitative characteristics were one of the main problems studied by the famous physicist M. Faraday for a long time. In particular, with the help of numerous experiments, he managed to prove that the mass of the substance released during electrolysis directly depends on the amount of electricity and the time during which this electrolysis was carried out. From any other reasons, with the exception of the type of substance, this mass does not depend.

In addition, studying the current in liquids, Faraday experimentally found out that the same amount is needed to isolate one kilogram of any substance during electrolysis. This amount, equal to 9.65.10 7 k, was called the Faraday number.

Unlike metal conductors, the electric current in liquids is surrounded, which greatly complicates the movement of the ions of the substance. In this regard, in any electrolyte, only a small voltage can be generated. At the same time, if the temperature of the solution rises, then its conductivity increases, and the field increases.

Electrolysis has another interesting property. The thing is that the probability of the decay of a particular molecule into positive and negative charged ions is the higher, the more molecules of the substance itself and the solvent. At the same time, at a certain moment, the solution becomes supersaturated with ions, after which the conductivity of the solution begins to decrease. Thus, the strongest will take place in a solution where the concentration of ions is extremely low, but the electric current in such solutions will be extremely low.

The electrolysis process found wide application in various industrial productions related to electrochemical reactions. Among the most important of these are the production of metal using electrolytes, the electrolysis of salts containing chlorine and its derivatives, redox reactions, the production of such a necessary substance as hydrogen, surface polishing, and electroplating. For example, at many enterprises of mechanical engineering and instrument making, the refining method is very common, which is the production of metal without any unnecessary impurities.

With regard to their electrical properties fluids are very versatile. Molten metals, like metals in the solid state, have a high electrical conductivity associated with a high concentration of free electrons.

Many liquids, such as pure water, alcohol, kerosene, are good dielectrics, since their molecules are electrically neutral and there are no free charge carriers in them.

electrolytes. A special class of liquids are the so-called electrolytes, which include aqueous solutions inorganic acids, salts and bases, melts of ionic crystals, etc. Electrolytes are characterized by the presence of high concentrations of ions, which make it possible for an electric current to pass. These ions arise during melting and during dissolution, when, under the influence of the electric fields of the solvent molecules, the molecules of the solute are decomposed into separate positively and negatively charged ions. This process is called electrolytic dissociation.

electrolytic dissociation. The degree of dissociation a of a given substance, i.e., the proportion of molecules of the solute decomposed into ions, depends on the temperature, concentration of the solution, and the permittivity of the solvent. As the temperature increases, the degree of dissociation increases. Ions of opposite signs can recombine, uniting again into neutral molecules. Under constant external conditions, a dynamic equilibrium is established in the solution, in which the processes of recombination and dissociation compensate each other.

Qualitatively, the dependence of the degree of dissociation a on the concentration of the solute can be established using the following simple reasoning. If a unit volume contains molecules of a solute, then some of them are dissociated, and the rest are not dissociated. The number of elementary acts of dissociation per unit volume of the solution is proportional to the number of unsplit molecules and therefore equals where A is a coefficient depending on the nature of the electrolyte and temperature. The number of recombination acts is proportional to the number of collisions of unlike ions, i.e., proportional to the number of both those and other ions. Therefore, it is equal to where B is a coefficient that is constant for a given substance at a certain temperature.

In a state of dynamic equilibrium

The ratio does not depend on the concentration It can be seen that the lower the concentration of the solution, the closer a is to unity: in very dilute solutions, almost all molecules of the solute are dissociated.

The higher the dielectric constant of the solvent, the more weakened ionic bonds in the molecules of the solute and, therefore, the greater the degree of dissociation. So, hydrochloric acid gives an electrolyte with high electrical conductivity when dissolved in water, while its solution in ethyl ether is a very poor conductor of electricity.

Unusual electrolytes. There are also very unusual electrolytes. For example, the electrolyte is glass, which is a highly supercooled liquid with an enormous viscosity. When heated, the glass softens and its viscosity is greatly reduced. The sodium ions present in the glass acquire a noticeable mobility, and the passage of an electric current becomes possible, although glass is a good insulator at ordinary temperatures.

Rice. 106. Demonstration of the electrical conductivity of glass when heated

A clear demonstration of this can serve as an experiment, the scheme of which is shown in Fig. 106. A glass rod is connected to the lighting network through a rheostat While the rod is cold, the current in the circuit is negligible due to the high resistance of the glass. If the stick is heated with a gas burner to a temperature of 300-400 ° C, then its resistance will drop to several tens of ohms and the light bulb filament L will become hot. Now you can short-circuit the light bulb with key K. In this case, the resistance of the circuit will decrease and the current will increase. Under such conditions, the stick will be effectively heated by electric current and heated to a bright glow, even if the burner is removed.

Ionic conduction. The passage of electric current in the electrolyte is described by Ohm's law

An electric current in the electrolyte occurs at an arbitrarily small applied voltage.

The charge carriers in the electrolyte are positively and negatively charged ions. The mechanism of electrical conductivity of electrolytes is in many respects similar to the mechanism of electrical conductivity of gases described above. The main differences are due to the fact that in gases the resistance to the movement of charge carriers is mainly due to their collisions with neutral atoms. In electrolytes, the mobility of ions is due to internal friction - viscosity - when they move in a solvent.

As the temperature rises, the conductivity of electrolytes, in contrast to metals, increases. This is due to the fact that with increasing temperature, the degree of dissociation increases and the viscosity decreases.

Unlike electronic conductivity, which is characteristic of metals and semiconductors, where the passage of an electric current is not accompanied by any change chemical composition substances, ionic conductivity is associated with the transfer of matter

and the release of substances that are part of the electrolytes on the electrodes. This process is called electrolysis.

Electrolysis. When a substance is released on the electrode, the concentration of the corresponding ions in the electrolyte region adjacent to the electrode decreases. Thus, the dynamic balance between dissociation and recombination is disturbed here: it is here that the decomposition of the substance occurs as a result of electrolysis.

Electrolysis was first observed in the decomposition of water by current from voltaic column. A few years later, the famous chemist G. Davy discovered sodium, separating it by electrolysis from caustic soda. The quantitative laws of electrolysis were experimentally established by M. Faraday in They are easy to justify based on the mechanism of the phenomenon of electrolysis.

Faraday's laws. Each ion has an electric charge that is a multiple of the elementary charge e. In other words, the charge of the ion is , where is an integer equal to the valency of the corresponding chemical element or compound. Let ions be released during the passage of current at the electrode. Their charge on absolute value equal to Positive ions reach the cathode and their charge is neutralized by electrons flowing to the cathode through the wires from the current source. Negative ions approach the anode and the same number of electrons go through the wires to the current source. In this case, a charge passes through a closed electrical circuit

Let us denote by the mass of the substance released on one of the electrodes, and by the mass of the ion (atom or molecule). It is obvious that, therefore, Multiplying the numerator and denominator of this fraction by the Avogadro constant, we get

where is the atomic or molar mass, the Faraday constant, given by

From (4) it can be seen that the Faraday constant has the meaning of "one mole of electricity", i.e., it is the total electric charge of one mole of elementary charges:

Formula (3) contains both Faraday's laws. She says that the mass of the substance released during electrolysis is proportional to the charge passed through the circuit (Faraday's first law):

The coefficient is called the electrochemical equivalent of a given substance and is expressed as

kilograms per pendant It has the meaning of the reciprocal of the specific charge of the ion.

The electrochemical equivalent to is proportional to the chemical equivalent of the substance (Faraday's second law).

Faraday's laws and elementary charge. Since at the time of Faraday the concept of the atomic nature of electricity did not yet exist, the experimental discovery of the laws of electrolysis was far from trivial. On the contrary, it was Faraday's laws that essentially served as the first experimental proof of the validity of these ideas.

Measurement by experience Faraday constant made it possible for the first time to obtain a numerical estimate of the value of the elementary charge long before direct measurements of the elementary electric charge in Millikan's experiments with oil drops. It is remarkable that the idea of ​​the atomic structure of electricity received unequivocal experimental confirmation in experiments on electrolysis carried out in the 30s of the 19th century, when even the idea of ​​the atomic structure of matter was not yet shared by all scientists. In a famous speech delivered to the Royal Society and dedicated to the memory of Faraday, Helmholtz commented on this circumstance in this way:

“If we admit the existence of atoms of chemical elements, then we cannot avoid the further conclusion that electricity, both positive and negative, is divided into certain elemental quantities, which behave like atoms of electricity.”

Chemical current sources. If any metal, such as zinc, is immersed in water, then a certain amount of positive zinc ions, under the influence of polar water molecules, will begin to move from the surface layer crystal lattice metal into water. As a result, zinc will be negatively charged, and water positively. A thin layer is formed at the interface between metal and water, called the electric double layer; there is a strong electric field in it, the intensity of which is directed from water to metal. This field prevents the further transition of zinc ions into water, and as a result, a dynamic equilibrium arises, in which the average number of ions coming from the metal to the water is equal to the number of ions returning from the water to the metal.

Dynamic equilibrium will also be established if the metal is immersed in water solution salts of the same metal, such as zinc in a solution of zinc sulfate. In solution, the salt dissociates into ions. The resulting zinc ions are no different from the zinc ions that enter the solution from the electrode. An increase in the concentration of zinc ions in the electrolyte facilitates the transition of these ions into the metal from solution and makes it difficult

transition from metal to solution. Therefore, in a solution of zinc sulfate, the immersed zinc electrode, although charged negatively, is weaker than in pure water.

When a metal is immersed in a solution, the metal is not always negatively charged. For example, if a copper electrode is immersed in a solution of copper sulphate, then ions will begin to precipitate from the solution on the electrode, charging it positively. The field strength in the electric double layer in this case is directed from copper to the solution.

Thus, when a metal is immersed in water or in an aqueous solution containing ions of the same metal, a potential difference arises at the interface between the metal and the solution. The sign and magnitude of this potential difference depends on the type of metal (copper, zinc, etc.) on the concentration of ions in the solution and is almost independent of temperature and pressure.

Two electrodes made of different metals, immersed in an electrolyte, form a galvanic cell. For example, in the Volta element, the zinc and copper electrodes are immersed in an aqueous solution of sulfuric acid. At the first moment, the solution contains neither zinc ions nor copper ions. However, later these ions enter the solution from the electrodes and a dynamic equilibrium is established. As long as the electrodes are not connected to each other by a wire, the electrolyte potential is the same at all points, and the potentials of the electrodes differ from the electrolyte potential due to the formation of double layers at their border with the electrolyte. In this case, the electrode potential of zinc is -0.763 V, and copper. The electromotive force of the Volt element, which is made up of these potential jumps, will be equal to

Current in a circuit with a galvanic cell. If the electrodes of a galvanic cell are connected with a wire, then the electrons will pass through this wire from the negative electrode (zinc) to the positive one (copper), which disrupts the dynamic balance between the electrodes and the electrolyte in which they are immersed. Zinc ions will begin to move from the electrode into solution, so as to maintain the electric double layer in the same state with a constant potential jump between the electrode and electrolyte. Similarly, at the copper electrode, copper ions will begin to move out of solution and deposit on the electrode. In this case, a deficiency of ions is formed near the negative electrode, and an excess of such ions is formed near the positive electrode. Total number ions in solution will not change.

As a result of the described processes, an electric current will be maintained in a closed circuit, which is created in the connecting wire by the movement of electrons, and in the electrolyte by ions. When an electric current is passed, the zinc electrode gradually dissolves and copper is deposited on the positive (copper) electrode.

electrode. The concentration of ions increases at the zinc electrode and decreases at the copper one.

Potential in a circuit with a galvanic cell. The described picture of the passage of electric current in an inhomogeneous closed circuit containing chemical element, corresponds to the potential distribution along the circuit, shown schematically in fig. 107. In an external circuit, i.e., in the wire connecting the electrodes, the potential gradually decreases from the value at the positive (copper) electrode A to the value at the negative (zinc) electrode B in accordance with Ohm's law for a homogeneous conductor. In the internal circuit, i.e., in the electrolyte between the electrodes, the potential gradually decreases from the value near the zinc electrode to the value near the copper electrode. If in the external circuit the current flows from the copper electrode to the zinc electrode, then inside the electrolyte - from zinc to copper. Potential jumps in electrical double layers are created as a result of the action of external (in this case, chemical) forces. The movement of electric charges in double layers due to external forces occurs against the direction of action of electric forces.

Rice. 107. Potential distribution along a chain containing a chemical element

The inclined sections of the potential change in fig. 107 correspond to the electrical resistance of the external and internal sections of the closed circuit. The total potential drop along these sections is equal to the sum of the potential jumps in the double layers, i.e., the electromotive force of the element.

The passage of electric current in a galvanic cell is complicated by by-products released on the electrodes and the appearance of a concentration drop in the electrolyte. These phenomena are referred to as electrolytic polarization. For example, in the Volta elements, when the circuit is closed, positive ions move towards the copper electrode and are deposited on it. As a result, after some time, the copper electrode is, as it were, replaced by a hydrogen one. Since the electrode potential of hydrogen is 0.337 V lower than the electrode potential of copper, the EMF of the element decreases by about the same amount. In addition, the hydrogen released on the copper electrode increases the internal resistance of the element.

For decreasing harmful influence hydrogen used depolarizers - various oxidizers. For example, in the most common element Leklanshe ("dry" batteries)

the positive electrode is a graphite rod surrounded by a compressed mass of manganese peroxide and graphite.

Batteries. A practically important variety of galvanic cells are batteries, for which, after discharging, a reverse charging process is possible with the conversion of electrical energy into chemical energy. Substances consumed when receiving electric current are restored inside the battery by electrolysis.

It can be seen that when the battery is charged, the concentration of sulfuric acid increases, which leads to an increase in the density of the electrolyte.

Thus, during the charging process, a sharp asymmetry of the electrodes is created: one becomes lead, the other from lead peroxide. A charged battery is a galvanic cell capable of serving as a current source.

When consumers of electrical energy are connected to the battery, an electric current will flow through the circuit, the direction of which is opposite to the charging current. chemical reactions go in the opposite direction and the battery returns to its original state. Both electrodes will be covered with a layer of salt, and the concentration of sulfuric acid will return to its original value.

A charged battery has an EMF of approximately 2.2 V. When discharging, it drops to 1.85 V. Further discharge is not recommended, since the formation of lead sulfate becomes irreversible and the battery deteriorates.

The maximum charge that a battery can give when discharging is called its capacity. Battery capacity typically

measured in ampere-hours. She is more than more surface plates.

electrolysis applications. Electrolysis is used in metallurgy. The most common electrolytic production of aluminum and pure copper. With the help of electrolysis, it is possible to create thin layers of some substances on the surface of others in order to obtain decorative and protective coatings (nickel plating, chromium plating). The process of obtaining peelable coatings (galvanoplasty) was developed by the Russian scientist B. S. Yakobi, who applied it to the manufacture of hollow sculptures that adorn Saint Isaac's Cathedral in St. Petersburg.

What is the difference between the physical mechanism of electrical conductivity in metals and electrolytes?

Explain why the degree of dissociation of a given substance depends on the permittivity of the solvent.

Explain why in highly dilute electrolyte solutions almost all solute molecules are dissociated.

Explain how the mechanism of electrical conductivity of electrolytes is similar to the mechanism of electrical conductivity of gases. Why, under constant external conditions, the electric current is proportional to the applied voltage?

What role does the law of conservation of electric charge play in deriving the law of electrolysis (3)?

Explain the relationship between the electrochemical equivalent of a substance and the specific charge of its ions.

How can one experimentally determine the ratio of electrochemical equivalents different substances if there are several electrolytic baths, but there are no instruments for measuring current strength?

How can the phenomenon of electrolysis be used to create an electricity consumption meter in a DC network?

Why can Faraday's laws be considered as experimental proof of the ideas about the atomic nature of electricity?

What processes occur when metal electrodes are immersed in water and in an electrolyte containing ions of these metals?

Describe the processes occurring in the electrolyte near the electrodes of a galvanic cell during the passage of current.

Why do positive ions inside a galvanic cell move from the negative (zinc) electrode to the positive (copper) electrode? How does a potential distribution arise in the circuit that causes the ions to move in this way?

Why can the degree of charge of an acid battery be checked using a hydrometer, i.e. a device for measuring the density of a liquid?

What is the fundamental difference between processes in batteries and processes in "dry" batteries?

What part of the electrical energy expended in the process of charging the battery c can be used when discharging it, if during the process of charging the battery, voltage was maintained at its terminals

Electron current in liquids

In an iron conductor, an electronic current appears by the directed movement of free electrons, and that with all this, no changes in the substance from which the conductor is made occur.

Such conductors, in which the passage of an electron current is not accompanied by chemical changes in their substance, are called conductors of the first kind. These include all metals, coal and a number of other substances.

But there are also such conductors of electronic current in nature, in which chemical phenomena occur during the passage of current. These conductors are called conductors of the second kind. These include mainly different mixtures of acids, salts and alkalis in water.

If you pour water into a glass vessel and add a few drops of sulfuric acid (or some other acid or alkali) to it, and then take two iron plates and attach conductors to them by lowering these plates into the vessel, and connect a current source to the other ends of the conductors through a switch and an ammeter, then gas will be released from the solution, while it will last continuously until the circuit is closed. acidified water is indeed a conductor. In addition, the plates will begin to be covered with gas bubbles. Then these bubbles will break away from the plates and come out.

When an electron current passes through the solution, chemical changes occur, as a result of which gas is released.

Conductors of the second kind are called electrolytes, and the phenomenon that occurs in an electrolyte when an electronic current passes through it is.

Iron plates immersed in an electrolyte are called electrodes; one of them, connected to the positive pole of the current source, is called the anode, and the other, connected to the negative pole, is the cathode.

What is the reason for the passage of an electron current in a watery conductor? It turns out that in such mixtures (electrolytes), acid molecules (alkalis, salts) under the action of a solvent (in this case, water) decompose into two components, while one part of the molecule has a positive electronic charge, and the other negative.

The particles of a molecule that have an electronic charge are called ions. When an acid, salt or alkali is dissolved in water, a great amount both positive and negatively charged ions.

Now it should become clear why an electronic current passed through the solution, because a potential difference was created between the electrodes connected to the current source, in other words, one of them turned out to be positively charged and the other negatively. Under the influence of this potential difference, positive ions began to move towards the negative electrode - the cathode, and negative ions - towards the anode.

Thus, the chaotic movement of ions has become an ordered counter-movement of negatively charged ions in one direction and positive ones in the other. This process of charge transfer constitutes the flow of the electron current through the electrolyte and occurs as long as there is a potential difference across the electrodes. With the disappearance of the potential difference, the current through the electrolyte stops, the orderly movement of ions is disturbed, and chaotic movement sets in again.

As an example, consider the phenomenon of electrolysis when an electron current is passed through a solution of copper sulphate CuSO4 with copper electrodes lowered into it.

The phenomenon of electrolysis when current passes through a solution of copper sulphate: C - vessel with electrolyte, B - current source, C - switch

There will also be a counter movement of ions to the electrodes. The positive ion will be the copper (Cu) ion, and the negative ion will be the acid residue (SO4) ion. Copper ions, upon contact with the cathode, will be discharged (attaching the missing electrons to themselves), i.e., they will be converted into neutral molecules of pure copper, and deposited on the cathode in the form of the thinnest (molecular) layer.

Negative ions, having reached the anode, are also discharged (give away extra electrons). But with all this, they enter into a chemical reaction with the copper of the anode, as a result of which a molecule of copper Cu is attached to the acidic residue SO4 and a molecule of copper sulfate CuS O4 appears, which is returned back to the electrolyte.

Because this chemical process takes a long time, copper is deposited on the cathode, which is released from the electrolyte. With all this, the electrolyte, instead of the copper molecules that have gone to the cathode, receives new copper molecules due to the dissolution of the second electrode - the anode.

The same process occurs if zinc electrodes are taken instead of copper ones, and the electrolyte is a solution of zinc sulfate Zn SO4. Zinc will also be transferred from the anode to the cathode.

In such a way, difference between electronic current in metals and watery conductors consists in the fact that in metals only free electrons, i.e., negative charges, are charge carriers, while in electrolytes electricity is carried by oppositely charged particles of matter - ions moving in opposite directions. That's why they say that electrolytes have ionic conductivity.

The phenomenon of electrolysis was discovered in 1837 by B. S. Jacobi, who created countless experiments on the study and improvement of chemical current sources. Jacobi found that one of the electrodes placed in a solution of copper sulphate, when an electron current passes through it, is covered with copper.

This phenomenon is called electroplating, finds on this moment very huge practical use. One example of this is the coating of iron objects with a thin layer of other metals, i.e. nickel plating, gilding, silver plating, etc.

Gases (including air) do not conduct electron current under normal conditions. For example, naked wires of overhead lines, being suspended parallel to each other, are isolated from one another by a layer of air.

But under the influence of the highest temperature, a large potential difference and other circumstances, gases, like watery conductors, ionize, that is, particles of gas molecules appear in them in large quantities, which, being carriers of electricity, facilitate the passage of electron current through the gas.

But at the same time, the ionization of a gas differs from the ionization of a watery conductor. If in water a molecule breaks up into two charged parts, then in gases, under the action of ionization, electrons are always separated from each molecule and an ion remains in the form of a positively charged part of the molecule.

As soon as the ionization of a gas is completed, it ceases to be conductive, while a liquid always remains a conductor of electron current. As follows, the conductivity of a gas is a temporary phenomenon, depending on the action of external circumstances.

But there is another kind of discharge called arc discharge or just an electronic arc. The phenomenon of an electronic arc was discovered at the beginning of the 19th century by the first Russian electrical engineer V. V. Petrov.

V. V. Petrov, doing countless experiments, found that between 2 charcoal connected to a current source, a continuous electronic discharge appears through the air, accompanied by a bright light. In his own writings, V. V. Petrov wrote that with all this, “black peace can be quite brightly illuminated.” So for the first time electronic light was obtained, which was actually used by another Russian electrical scientist Pavel Nikolaevich Yablochkov.

"Yablochkov's Candle", whose work is based on the use of an electronic arc, made a real revolution in electrical engineering in those days.

The arc discharge is used as a light source in our days, for example, in searchlights and projectors. The highest temperature of the arc discharge allows it to be used for the construction of an arc furnace. Currently, arc furnaces powered by current are very great strength, are used in a number of industries: for smelting steel, cast iron, ferroalloys, bronze, etc. And in 1882, N. N. Benardos for the first time used an arc discharge for cutting and welding metal.

In gas tubes, fluorescent lamps, voltage stabilizers, to obtain electric and ion beams, the so-called glow gas discharge.

The spark discharge is used to measure huge potential differences with the help of a spherical spark gap, the electrodes of which are two iron balls with a polished surface. The balls are moved apart, and a measured potential difference is applied to them. Then the balls are brought together until a spark jumps between them. Knowing the diameter of the balls, the distance between them, the pressure, temperature and humidity of the air, they find the potential difference between the balls according to special tables. In this way, it is possible to determine, with an accuracy of several percent, a potential difference of the order of 10 thousand volts.

That's all for now. Well, if you want to find out more, I recommend paying attention to Misha Vanyushin's CD:

"About electricity for beginners in video format on DVD"