Electrolytes as chemicals have been known since ancient times. However, they have conquered most of their areas of application relatively recently. We will discuss the highest priority areas for the industry to use these substances and figure out what the latter are and how they differ from each other. But let's start with a digression into history.
History
The oldest known electrolytes are s alts and acids discovered in the ancient world. However, ideas about the structure and properties of electrolytes have evolved over time. Theories of these processes have evolved since the 1880s, when a number of discoveries were made related to theories of the properties of electrolytes. There have been several qualitative leaps in theories describing the mechanisms of the interaction of electrolytes with water (after all, only in solution do they acquire the properties due to which they are used in industry).
Now we will analyze in detail several theories that have had the greatest influence on the development of ideas about electrolytes and their properties. And let's start with the most common and simple theory that each of us took in school.
Arrhenius Theory of Electrolytic Dissociation
in 1887Swedish chemist Svante Arrhenius and Russian-German chemist Wilhelm Ostwald created the theory of electrolytic dissociation. However, everything is not so simple here either. Arrhenius himself was a supporter of the so-called physical theory of solutions, which did not take into account the interaction of the constituent substances with water and argued that there are free charged particles (ions) in the solution. By the way, it is from such positions that electrolytic dissociation is considered at school today.
Let's still talk about what this theory gives and how it explains to us the mechanism of interaction of substances with water. Like everyone else, she has several postulates that she uses:
1. When interacting with water, the substance decomposes into ions (positive - cation and negative - anion). These particles undergo hydration: they attract water molecules, which, by the way, are positively charged on one side and negatively charged on the other (form a dipole), as a result, they form into aqua complexes (solvates).
2. The process of dissociation is reversible - that is, if the substance has broken up into ions, then under the influence of any factors it can again turn into the original one.
3. If you connect electrodes to the solution and start a current, then the cations will begin to move towards the negative electrode - the cathode, and the anions towards the positively charged - the anode. That is why substances that are highly soluble in water conduct electricity better than water itself. They are also called electrolytes for the same reason.
4. The degree of dissociation of the electrolyte characterizes the percentage of the substance that has undergone dissolution. Thisthe indicator depends on the properties of the solvent and the solute itself, on the concentration of the latter and on the external temperature.
Here, in fact, and all the basic postulates of this simple theory. We will use them in this article to describe what happens in an electrolyte solution. We will analyze examples of these compounds a little later, but now we will consider another theory.
Lewis theory of acids and bases
According to the theory of electrolytic dissociation, an acid is a substance in which a hydrogen cation is present, and a base is a compound that decomposes into a hydroxide anion in solution. There is another theory named after the famous chemist Gilbert Lewis. It allows you to somewhat expand the concept of acid and base. According to the Lewis theory, acids are ions or molecules of a substance that have free electron orbitals and are able to accept an electron from another molecule. It is easy to guess that the bases will be such particles that are able to donate one or more of their electrons to the "use" of the acid. It is very interesting here that not only an electrolyte, but also any substance, even insoluble in water, can be an acid or base.
Brandsted-Lowry protolithic theory
In 1923, independently of each other, two scientists - J. Bronsted and T. Lowry - proposed a theory that is now actively used by scientists to describe chemical processes. The essence of this theory is thatdissociation is reduced to the transfer of a proton from an acid to a base. Thus, the latter is understood here as a proton acceptor. Then the acid is their donor. The theory also explains well the existence of substances that exhibit the properties of both acids and bases. Such compounds are called amphoteric. In the Bronsted-Lowry theory, the term ampholytes is also used for them, while acids or bases are usually called protoliths.
We have come to the next part of the article. Here we will tell you how strong and weak electrolytes differ from each other and discuss the influence of external factors on their properties. And then we will begin to describe their practical application.
Strong and weak electrolytes
Each substance interacts with water individually. Some dissolve well in it (for example, table s alt), while some do not dissolve at all (for example, chalk). Thus, all substances are divided into strong and weak electrolytes. The latter are substances that interact poorly with water and settle at the bottom of the solution. This means that they have a very low degree of dissociation and a high bond energy, which under normal conditions does not allow the molecule to decompose into its constituent ions. The dissociation of weak electrolytes occurs either very slowly, or with an increase in temperature and concentration of this substance in solution.
Let's talk about strong electrolytes. These include all soluble s alts, as well as strong acids and alkalis. They easily break up into ions and it is very difficult to collect them in precipitation. The current in electrolytes, by the way, is conductedprecisely because of the ions contained in the solution. Therefore, strong electrolytes conduct current best of all. Examples of the latter: strong acids, alkalis, soluble s alts.
Factors affecting the behavior of electrolytes
Now let's figure out how changes in the external environment affect the properties of substances. The concentration directly affects the degree of electrolyte dissociation. Moreover, this ratio can be expressed mathematically. The law describing this relationship is called the Ostwald dilution law and is written as follows: a=(K / c)1/2. Here a is the degree of dissociation (taken in fractions), K is the dissociation constant, which is different for each substance, and c is the concentration of the electrolyte in the solution. By this formula, you can learn a lot about the substance and its behavior in solution.
But we digress. In addition to concentration, the degree of dissociation is also affected by the temperature of the electrolyte. For most substances, increasing it increases solubility and reactivity. This can explain the occurrence of some reactions only at elevated temperatures. Under normal conditions, they go either very slowly, or in both directions (such a process is called reversible).
We have analyzed the factors that determine the behavior of a system such as an electrolyte solution. Now let's move on to the practical application of these, no doubt, very important chemicals.
Industrial use
Of course, everyone has heard the word "electrolyte"in relation to batteries. The car uses lead-acid batteries, the electrolyte in which is 40% sulfuric acid. To understand why this substance is needed there at all, it is worth understanding the features of the batteries.
So what is the principle of any battery? In them, a reversible reaction of the transformation of one substance into another occurs, as a result of which electrons are released. When the battery is charged, an interaction of substances takes place, which is not obtained under normal conditions. This can be represented as the accumulation of electricity in a substance as a result of a chemical reaction. When the discharge begins, the reverse transformation begins, leading the system to the initial state. These two processes together constitute one charge-discharge cycle.
Let's consider the above process on a specific example - a lead-acid battery. As you might guess, this current source consists of an element containing lead (as well as lead dioxide PbO2) and acid. Any battery consists of electrodes and the space between them, filled just with electrolyte. As the last, as we have already found out, in our example, sulfuric acid with a concentration of 40 percent is used. The cathode of such a battery is made of lead dioxide, and the anode is made of pure lead. All this is because different reversible reactions occur on these two electrodes with the participation of ions into which the acid has dissociated:
- PbO2 + SO42-+ 4H+ + 2e-=PbSO4 + 2H2O(reaction occurring at the negative electrode - cathode).
- Pb + SO42- - 2e-=PbSO 4 (Reaction at the positive electrode - anode).
If we read the reactions from left to right - we get the processes that occur when the battery is discharged, and if from right to left - when charging. In each chemical current source, these reactions are different, but the mechanism of their occurrence is generally described in the same way: two processes occur, in one of which electrons are "absorbed", and in the other, on the contrary, they "leave". The most important thing is that the number of absorbed electrons is equal to the number of emitted ones.
Actually, in addition to batteries, there are many applications of these substances. In general, electrolytes, examples of which we have given, are just a grain of the variety of substances that are combined under this term. They surround us everywhere, everywhere. Take, for example, the human body. Do you think these substances are not there? You are very mistaken. They are everywhere in us, and the largest amount is blood electrolytes. These include, for example, iron ions, which are part of hemoglobin and help transport oxygen to the tissues of our body. Blood electrolytes also play a key role in the regulation of water-s alt balance and heart function. This function is performed by potassium and sodium ions (there is even a process that occurs in cells, which is called the potassium-sodium pump).
Any substance that you can dissolve even a little is electrolytes. And there is no such industry and our life with you, wherewhatever they are applied. This is not only batteries in cars and batteries. This is any chemical and food production, military plants, clothing factories and so on.
The composition of the electrolyte, by the way, is different. So, it is possible to distinguish acidic and alkaline electrolyte. They fundamentally differ in their properties: as we have already said, acids are proton donors, and alkalis are acceptors. But over time, the composition of the electrolyte changes due to the loss of part of the substance, the concentration either decreases or increases (it all depends on what is lost, water or electrolyte).
We encounter them every day, but few people know exactly the definition of such a term as electrolytes. We have covered examples of specific substances, so let's move on to a little more complex concepts.
Physical properties of electrolytes
Now about physics. The most important thing to understand when studying this topic is how current is transmitted in electrolytes. Ions play a decisive role in this. These charged particles can transfer charge from one part of the solution to another. So, anions always tend to the positive electrode, and cations - to the negative. Thus, acting on the solution with an electric current, we separate the charges on different sides of the system.
Very interesting is such a physical characteristic as density. Many properties of the compounds we are discussing depend on it. And the question often pops up: "How to raise the density of the electrolyte?" In fact, the answer is simple: you need to downgrade the contentwater in solution. Since the density of the electrolyte is largely determined by the density of sulfuric acid, it largely depends on the concentration of the latter. There are two ways to carry out the plan. The first is quite simple: boil the electrolyte contained in the battery. To do this, you need to charge it so that the temperature inside rises slightly above one hundred degrees Celsius. If this method does not help, do not worry, there is another one: simply replace the old electrolyte with a new one. To do this, drain the old solution, clean the insides of sulfuric acid residues with distilled water, and then pour in a new portion. As a rule, high-quality electrolyte solutions immediately have the desired concentration. After replacement, you can forget for a long time about how to increase the density of the electrolyte.
The composition of the electrolyte largely determines its properties. Characteristics such as electrical conductivity and density, for example, are highly dependent on the nature of the solute and its concentration. There is a separate question about how much electrolyte can be in the battery. In fact, its volume is directly related to the declared power of the product. The more sulfuric acid inside the battery, the more powerful it is, i.e. the more voltage it can produce.
Where does it come in handy?
If you are a car enthusiast or just into cars, then you yourself understand everything. Surely you even know how to determine how much electrolyte is in the battery now. And if you are far from cars, then knowledgeproperties of these substances, their applications and how they interact with each other will not be superfluous at all. Knowing this, you will not be at a loss if you are asked to say which electrolyte is in the battery. Although even if you are not a car enthusiast, but you have a car, then knowing the battery device will not be superfluous at all and will help you with repairs. It will be much easier and cheaper to do everything yourself than to go to the auto center.
And in order to better study this topic, we recommend reading a chemistry textbook for schools and universities. If you know this science well and have read enough textbooks, Varypaev's "Chemical Current Sources" would be the best option. It outlines in detail the whole theory of the operation of batteries, various batteries and hydrogen cells.
Conclusion
We have come to the end. Let's summarize. Above, we have analyzed everything related to such a concept as electrolytes: examples, theory of structure and properties, functions and applications. Once again it is worth saying that these compounds are part of our life, without which our bodies and all areas of industry could not exist. Do you remember blood electrolytes? Thanks to them we live. What about our cars? With this knowledge, we will be able to fix any problem related to the battery, as now we understand how to increase the density of the electrolyte in it.
It's impossible to tell everything, and we didn't set such a goal. After all, this is not all that can be said about these amazing substances.
