The mass concentration of a solution is one of the common concepts in modern chemistry. In the article we will identify the features of solutions, their types, application. Let us note some examples of calculating different types of concentrations.
Features of solutions
Solution is a homogeneous system with a variable composition. Of the two components of a solution, one always acts as a medium. It is in it that the structural fragments of other substances will dissolve. It is called a solvent, inside which the molecules of the solute are located.
If two gaseous substances are mixed, then no solvent is emitted. Special calculations are always made for each specific situation.
Obtaining homogeneous systems
To obtain homogeneous solutions, it is necessary to crush the dissolved substances to structural units. Only then will the systems be true. When crushed to small droplets, grains of sand, which will be distributed in the medium, colloidal solutions, emulsions, suspensions are obtained.
Using solutions
By the way, inconstruction, a mixture of sand, cement, water is also called a solution, but from a chemical point of view, it is a suspension. The practical importance of solutions can be explained for various reasons.
Chemical reactions in liquid solutions occur in the bulk of the solvent. This makes them available for reaction without any additional action on the system. In a mixture containing solid particles, it is impossible to carry out the reaction in full. To speed up the process, the particles will need to touch at some points. To increase the reaction rate, the crystals are ground in a mortar, then they are pressed. But it is not immediately possible to achieve the completeness of the process.
In a solution, the process proceeds differently. Molecules move freely, and when they collide, chemical transformations occur. The energy that begins to be released in such an interaction is accumulated by the solvent, the system practically does not heat up.
Physical properties and concentration of solutions
The mass fraction of a substance allows you to determine the quantitative ratio of the solute and solvent taken for their preparation. Metal alloys, by the way, are also solutions, but solid, characterized by certain physical parameters.
Solutions have the ability to change the strength of the dissolved component. This makes them in demand in agriculture and medicine. For example, a solution of potassium permanganate (potassium permanganate) is used to treat abrasions and wounds in medium concentration. But practicalits low concentration is also important. Thus, a mass fraction of a substance of 2-3% gives the solution a slightly pink color, which is in demand for gastric lavage.
Dark purple crystals of potassium permanganate are not used for medical purposes because they have strong oxidizing properties. In general, the intensity of the color is directly related to what its concentration is. The mass fraction of the substance allows you to adjust the toxicity of the finished solution.
Mass fraction
How is this concentration calculated? The mass fraction of a substance is characterized by the ratio of the mass of the substance to the mass of the solution, taken as a percentage. Their organoleptic properties are influenced not only by what will dissolve, but also by a quantitative indicator. For example, for a weak solution of common s alt, there is almost no taste, and at high concentrations, it manifests itself to varying degrees.
How is concentration determined in practice? The mass fraction of a substance in a solution is considered in the school course of inorganic chemistry. Tasks for its determination are included in the test tasks for Grade 9 graduates.
Let's give an example of a task that uses concentration.
Mass fraction of table s alt 25%. The mass of the solution is 250 grams. Determine the mass of water contained in it. To perform calculations, you first need to find out the mass of the substance. Based on the proportion, we find that the substances in the solution are 62.5 grams. To determine the mass of water, subtract the mass of the substance itself from 250 grams, as a resultwe get 187.5 g.
Types of concentrations
What is concentration? Mass fractions in the solution may contain no more than one hundred percent. In chemistry, the term "concentration" implies a certain amount of a solute. There are several options: molar, mass concentration.
For example, if you need to prepare a solution of 80 grams of water and 20 grams of table s alt and determine the mass fractions of a substance in a solution, you first need to determine the mass of the solution. It will be one hundred grams. The percentage of the substance is 20 percent.
We analyzed what constitutes a mass fraction. Molar concentration refers to the ratio of the amount of a substance to the volume of the solution taken. To prepare a solution with a given molar concentration, the mass of the substance is first determined. Then it is weighed in the right amount and dissolved in a liter of solvent.
Calculation of molar concentration
So, to prepare 2 liters of a solution with a concentration of 0.15 mol/l, first calculate the mass of s alt contained in the solution. To do this, you need to divide 0.15 mol by 2 liters, we get 0.075 mol. Now we calculate the mass: 0.075 mol is multiplied by 58.5 g / mol. Result - 4, 39
Problems of Analytical Chemistry
An analysis is considered as an applied chemical problem. With its help, the composition of the mixture is revealed, diagnostic tests are carried out, and rocks are analyzed. To do this, you need to determine the qualitative and quantitative composition of the solution.
Among those tasks that are most often encountered in inorganic chemistry, we single out the determination of the concentration of one substance from a given value in another substance. With the help of experiments, it is possible to carry out a gradual addition to a solution, in which the molar concentration is known, of the desired solution. This process is called titration.
Solubility and solvents
The most common solvent is water. It perfectly dissolves bases, acids, s alts, some organic compounds. It is aqueous solutions that are the most common systems in nature. Water acts as a biological solvent. It is considered the basis for the flow of many media: blood, cytosols, intercellular fluids. Many types of animals and plants live in the aquatic environment.
Solubility is the property of a substance to dissolve in a chosen solvent. This is a complex phenomenon that requires taking into account certain nuances and structural features of the solvent.
Alcohols can be noted as good organic substances. They include hydroxyl groups in their composition, therefore they have high solubility.
Conclusion
Any liquid can be considered as a solvent. That is why we often talk about the mutual solubility of different liquid substances. For example, among organic substances one can mention the water solubility of esters.
Different types of concentrations used in inorganic and organic chemistry help to carry outqualitative and quantitative determinations of substances. The theory of solutions is in demand in analytical chemistry, pharmaceuticals and modern medicine.
