What is the normality of the solution? How to determine the normality of the solution? The formula for the normality of the solution

With solutions of different substances we meet every day. But it is unlikely that each of us represents how much these systems play. Much of their behavior has become clear today due to detailed study for millennia. During all this time, many terms were introduced that are incomprehensible to the common man. One of them is the normality of the solution. What it is? This will be discussed in our article. And we will start with immersion in the past.

History of research

The first bright minds that began the study of solutions were such well-known chemists as Arrhenius, Van't Hoff and Ostwald. Under the influence of their work, subsequent generations of chemists began to delve into the study of aqueous and dilute solutions. Of course, they have accumulated a huge body of knowledge, but non-aqueous solutions have remained without attention, which, by the way, play a big role both in industry and in other spheres of human life.

In the theory of non-aqueous solutions there were many incomprehensible. For example, if the value of conductivity increased with increasing dissociation , in analogous systems, but with a different solvent instead of water, everything was the other way around. Small values of electrical conductivity often correspond to high degrees of dissociation. Anomalies spurred scientists to explore this field of chemistry. A large body of data was accumulated, the processing of which allowed finding regularities that supplement the theory of electrolytic dissociation. In addition, it was possible to expand knowledge about electrolysis and the nature of complex ions of organic and inorganic compounds.

Then studies in the field of concentrated solutions began to be carried out more actively. Such systems differ significantly in properties from dilute ones due to the fact that when the concentration of the dissolved substance increases, an increasing role is played by its interaction with the solvent. More about this - in the next section.

Theory

At the moment, the theory of electrolytic dissociation best explains the behavior of ions, molecules, and atoms in solution. Since its creation by Svante Arrhenius in the 19th century, it has undergone some changes. Some laws were discovered (such as the Ostwald dilution law), which somewhat did not fit into the classical theory. But, thanks to the subsequent work of scientists, the theory was amended, and in the modern form it exists so far and with high accuracy describes the results obtained by experimental paths.

The main essence of the electrolytic theory of dissociation is that the substance dissolves into its constituent ions-particles that have a charge. Depending on the ability to decompose (dissociate) into parts, distinguish between strong and weak electrolytes. Strong, as a rule, completely dissociate into ions in solution, while weak ones - to a very small extent.

These particles, into which the molecule breaks up, can interact with the solvent. This phenomenon is called solvation. But it does not always happen, because it is due to the presence of a charge on the ion and molecules of the solvent. For example, a water molecule is a dipole, that is, a particle that is charged positively on one side, and negatively on the other. And the ions to which the electrolyte decays, also have a charge. Thus, these particles are attracted by differently charged sides. But this happens only with polar solvents (such is water). For example, in a solution of a substance in hexane, solvation will not occur.

To study solutions it is often necessary to know the amount of dissolved substance. In the formulas it is sometimes very inconvenient to substitute some quantities. Therefore, there are several types of concentrations, among which is the normality of the solution. Now we will tell in detail about all the ways of expressing the content of a substance in a solution and the methods for calculating it.

Concentration of solution

In chemistry, many formulas are used, and some of them are constructed in such a way that it is more convenient to take the value in a particular form.

The first and most familiar form of expression of concentration is the mass fraction. It is calculated very simply. We just need to divide the mass of matter in the solution into its total mass. So we get the answer in fractions of one. Multiplying the number by one hundred, we get the answer in percent.

A slightly less well-known form is the volume fraction. Most often it is used to express the concentration of alcohol in alcoholic beverages. It is also calculated quite simply: we divide the volume of the dissolved substance by the volume of the entire solution. Just like in the previous case, you can get the answer in percent. The labels often refer to: "40% vol.", Which means: 40 volume percent.

In chemistry, other types of concentration are often used. But before you go to them, let's talk about what a mole of matter. The amount of substance can be expressed in different ways: mass, volume. But the molecules of each substance have their own weight, and by the mass of the sample it is impossible to understand how many molecules there are in it, and this is necessary to understand the quantitative component of the chemical transformations. For this purpose, a quantity such as a mole of substance was introduced. In fact, one mole is a certain number of molecules: 6.02 * 10 ²³ . This is called the Avogadro number. Most often such unit, as mole of substance, is used for calculation of quantity of products of any reaction. In this regard, there is another form of expression of concentration - molarity. This is the amount of matter per unit volume. The molarity is expressed in mol / l (read: mole per liter).

There is very similar to the previous form of expression of the substance content in the system: molality. It differs from molarity in that it determines the amount of matter not in a unit of volume, but in a unit of mass. And expressed in moles per kilogram (or other multiples, for example per gram).

So we came to the last form, which we will discuss separately, since its description requires some theoretical information.

Normality of the solution

What is it? And what is different from the previous values? To begin with, it is necessary to understand the difference between such concepts as normality and molarity of solutions. In fact, they differ only by one value - the number of equivalence. Now you can even imagine what the normality of the solution is. It's just a modified molarity. The number of equivalence shows the number of particles capable of interacting with one mole of hydrogen ions or hydroxide ions.

We became acquainted with what is the normality of the solution. But it's worth digging deeper, and we'll see how simple this seemingly complex form of describing the concentration. So, let's take a closer look at the normality of the solution.

Formula

It is fairly easy to imagine a formula by a verbal description. It will look like this: С _н = z * n / N. Here, z is the equivalence factor, n is the amount of matter, and V is the volume of the solution. The first quantity is the most interesting. It just shows the equivalent of a substance, that is, the number of real or imaginary particles capable of reacting with one minimal particle of another substance. This, in fact, the normality of the solution, the formula of which was presented above, qualitatively differs from molarity.

And now let's move on to another important part: how to determine the normality of the solution. This is undoubtedly an important question, therefore it is worthwhile to approach this study with an understanding of each quantity indicated in the equation presented above.

How to find the normality of the solution?

The formula that we have discussed above is of a purely applied nature. All the quantities given in it can be easily calculated in practice. In fact, it is very easy to calculate the normality of a solution, knowing certain quantities: the mass of the dissolved substance, its formula and the volume of the solution. Since we know the formula of the molecules of matter, we can find its molecular mass. The ratio of the mass of the sample weighed to its molar mass will be equal to the number of moles of the substance. And knowing the volume of the whole solution, we can accurately say which molar concentration we have.

The next operation that we need to do in order to calculate the normality of the solution is an action to find an equivalence factor. To do this, we need to understand how dissociation results in the formation of particles capable of attaching protons or hydroxyl ions. For example, in sulfuric acid, the equiva- lence factor is 2, and, consequently, the normality of the solution in this case is calculated by simply multiplying by 2 its molarities.

Application

In chemical analytics, it is very often necessary to calculate the normality and molarity of solutions. This is very convenient for extracting the molecular formulas of substances.

What else to read?

To better understand what the normality of a solution is, it is best to open a textbook on general chemistry. And if you already know all this information, you should turn to the textbook on analytical chemistry for students of chemical specialties.

Conclusion

Thanks to the article, we think you understood that the normality of a solution is a form of expressing the concentration of a substance that is used mainly in chemical analysis. And now it's no secret to anyone how it is calculated.