We encounter solutions of various substances every day. But it is unlikely that each of us realizes how big a role these systems play. Much of their behavior has become clear today through detailed study over thousands of years. During all this time, many terms that are incomprehensible to the common man have been introduced. One of them is the normality of the solution. What it is? This will be discussed in our article. Let's start by diving into the past.
Research History
The first bright minds who began to study 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 amount of knowledge, but non-aqueous solutions were left without attention, which, by the way, also play a big role both in industry and in other areas of human life.
There was a lot of incomprehensibility in the theory of non-aqueous solutions. For example, if in aqueous systems the value of conductivity increased with an increase in the degree of dissociation, then in similar systems, but with a different solvent instead of water, it was the other way around. Small electric valuesconductivities often correspond to high degrees of dissociation. Anomalies spurred scientists to explore this area of chemistry. A large array of data was accumulated, the processing of which made it possible to find 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 more active research began in the field of concentrated solutions. Such systems significantly differ in properties from dilute ones due to the fact that with increasing concentration of the dissolved substance, its interaction with the solvent begins to play an increasingly important role. More on this in the next section.
Theory
At the moment, the best explanation of the behavior of ions, molecules and atoms in solution is only the theory of electrolytic dissociation. Since its creation by Svante Arrhenius in the 19th century, it has undergone some changes. Some laws were discovered (such as Ostwald's dilution law) that somewhat did not fit into the classical theory. But, thanks to the subsequent work of scientists, amendments were made to the theory, and in its modern form it still exists and describes the results obtained experimentally with high accuracy.
The main essence of the electrolytic theory of dissociation is that the substance, when dissolved, decomposes into its constituent ions - particles that have a charge. Depending on the ability to decompose (dissociate) into parts, there are strong and weakelectrolytes. Strong ones tend to completely dissociate into ions in solution, while weak ones only 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 occur, since 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 charged positively on one side and negatively charged on the other. And the ions into which the electrolyte decomposes 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 very often necessary to know the amount of a solute. It is sometimes very inconvenient to substitute certain 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 ways of expressing the content of a substance in a solution and methods for calculating it.
Concentration of solution
There are many formulas in chemistry, and some of them are constructed in such a way that it is more convenient to take the value in one particular form or another.
The first, and most familiar to us, 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 solution by its total mass. SoThus, we get the answer in fractions of one. Multiplying the resulting number by one hundred, we get the answer as a percentage.
A slightly lesser known form is 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 solute by the volume of the entire solution. As in the previous case, you can get the answer as a percentage. Labels often say: "40% vol.", which means: 40 volume percent.
In chemistry, other types of concentration are often used. But before moving on to them, let's talk about what a mole of a substance is. The amount of a substance can be expressed in different ways: mass, volume. But after all, 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, such a quantity as a mole of a substance was introduced. In fact, one mole is a certain number of molecules: 6.021023. This is called Avogadro's 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 expressing concentration - molarity. This is the amount of substance per unit volume. Molarity is expressed in mol/L (read: moles per liter).
There is a very similar type of expression for the content of a substance in a system: molality. It differs from molarity in that it determines the amount of a substance not in a unit of volume, but in a unit of mass. And expressed in prayersper kilogram (or other multiple, such as per gram).
So we come to the last form, which we will now discuss separately, since its description requires some theoretical information.
Solution normality
What is this? And how is it different from previous values? First you need to understand the difference between such concepts as normality and molarity of solutions. In fact, they differ only by one value - the equivalence number. Now you can even imagine what the normality of the solution is. It's just a modified molarity. The equivalence number indicates the number of particles that can interact with one mole of hydrogen ions or hydroxide ions.
We got acquainted with what is the normality of the solution. But after all, it is worth digging deeper, and we will see how simple this, at first glance, complex form of describing concentration is. So, let's take a closer look at what the normality of the solution is.
Formula
It's pretty easy to imagine a formula from a verbal description. It will look like this: Cn=zn/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. It just shows the equivalent of a substance, that is, the number of real or imaginary particles that can react with one minimal particle of another substance. By this, in fact, the normality of the solution, the formula of which was presented above, qualitatively differsfrom 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, so it is worth approaching its study with an understanding of each value indicated in the equation presented above.
How to find the normality of a solution?
The formula we discussed above is purely applied. All the values given in it are easily calculated in practice. In fact, it is very easy to calculate the normality of a solution, knowing some quantities: the mass of the solute, its formula and the volume of the solution. Since we know the formula of the molecules of a substance, we can find its molecular weight. The ratio of the mass of a sample of a solute to its molar mass will be equal to the number of moles of the substance. And knowing the volume of the entire solution, we can say for sure what our molar concentration is.
The next operation that we need to carry out 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 its molarity by 2.
Application
In chemical analytics, one often has to calculate the normality and molarity of solutions. This is very convenient forcalculation of 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 refer to the textbook on analytical chemistry for students of chemical speci alties.
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, which is used mainly in chemical analysis. And now it's not a secret to anyone how it is calculated.
