With solutions of various substances we meet every day. But it is unlikely that each of us imagines how big a role these systems play. Much of their behavior has become clear today through detailed study over millennia. For all this time, many terms have been introduced, incomprehensible to a simple person. One of them is the normality of the solution. What it is? This will be discussed in our article. And we will begin by diving into the past.
The first bright minds to start the study of solutions were such well-known chemists as Arrhenius, Van 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, which, by the way, also play a large role both in industry and in other spheres of human life, have gone unnoticed.
In the theory of non-aqueous solutions, there was much incomprehensible. For example, if in water, with an increase in the degree of dissociation, the conductivity increased, in analogous systems, but with a different solvent instead of water, it was the other way around. Small values of electrical conductivity often correspond to high degrees of dissociation. Anomalies spurred scientists to study this area of chemistry. A large body of data was accumulated, the processing of which allowed us to find patterns that complement the theory of electrolytic dissociation. In addition, it was possible to expand knowledge of 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 diluted ones due to the fact that with an increase in the concentration of the dissolved substance, its interaction with the solvent begins to play an increasingly important role. More on this in the next section.
At the moment, only the theory of electrolytic dissociation explains the best behavior of ions, molecules, and atoms in solution. Since its inception by Svante Arrhenius in the 19th century, it has undergone some changes. Some laws were discovered (such as the Ostwald dilution law), which did not fit somewhat into classical theory. But, thanks to the subsequent work of scientists, the theory was amended, and in its present form it still exists and describes with high accuracy the results obtained by experimental means.
The main essence of the electrolytic theory of dissociation is that a substance, when dissolved, decomposes into its constituent ions - particles having 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 - 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 solvent molecules. For example, a water molecule is a dipole, that is, a particle positively charged on one side and negatively charged on the other. And the ions into which the electrolyte decays also have a charge. Thus, these particles are attracted by oppositely charged sides. But this happens only with polar solvents (such is water). For example, in a solution of any substance in hexane, solvation will not occur.
To study solutions, it is often necessary to know the amount of solute. It is sometimes very inconvenient to substitute some quantities into formulas. 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 its calculation methods.
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 one or another specific 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 the substance in the solution by its total mass. Thus we get the answer in fractions of a unit. Multiplying the resulting 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. As in the previous case, you can get the answer in percent. The labels often indicate: "40% vol.", Which means: 40 volume percent.
Other types of concentration are often used in chemistry. But before we go to them, let's talk about what a mole of a substance is. 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 are in it, and this is necessary to understand the quantitative component of chemical transformations. For this, 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 a unit as a mole of a substance is used to calculate the amount of products of a reaction. In this regard, there is another form of expression of concentration - molarity. This is the amount of substance per unit volume. Molarity is expressed in mol / L (read: mol per liter).
There is very similar to the previous type of expression of the substance content in the system: molality. It differs from molarity in that it determines the amount of a substance not in a unit volume, but in a unit mass. And it is expressed in moles per kilogram (or another multiple, for example, per gram).
So we come to the last form, which we will now discuss separately, since its description requires a little theoretical information.
The normality of the solution
What is it? And how is it different from previous values? First you need to understand the difference between such concepts as the normality and molarity of solutions. In fact, they differ by only one amount - the number of equivalence. Now you can even imagine what the normality of the solution is. This is just a modified molarity. The equivalence number indicates the number of particles capable of interacting with one mole of hydrogen ions or hydroxide ions.
We got acquainted with what is the normality of the solution. But it’s worth digging deeper, and we will see how simple this seemingly complex form of describing concentration is. So, we will analyze in more detail what the normality of the solution is.
It is fairly easy to imagine a formula from a verbal description. It will look like this: Cn= z * n / N. Here z is the equivalence factor, n is the amount of substance, V is the volume of the solution. The first value is the most interesting. Just it 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, differs qualitatively from molarity.
And now let's move on to another important part: how to determine the normality of a solution. This is undoubtedly an important issue, therefore, it is worthwhile to study it with an understanding of each quantity indicated in the equation presented above.
How to find the normality of the solution?
The formula that we examined above is purely applied in nature. All values given in it are easily calculated in practice. In fact, it is very easy to calculate the normality of a solution, knowing some values: the mass of the dissolved substance, its formula and the volume of the solution. Since we know the formula of the molecules of a substance, we can find its molecular mass. The ratio of the mass of a sample of solute to its molar mass will be equal to the number of moles of substance. And knowing the volume of the whole solution, we can say for sure what our molar concentration is.
The next operation that we need to perform in order to calculate the normality of the solution is the action of finding the equivalence factor. To do this, we need to understand how many particles are formed as a result of dissociation that can attach protons or hydroxyl ions. For example, in sulfuric acid the equivalence factor is 2, and therefore, the normality of the solution in this case is calculated by simply multiplying by 2 its molarity.