In this branch of science, molality is known with the concentration of a substance, with which it is possible to determine how much solute is needed to be able to dissolve another substance, it should be noted that this is a unit provided by the International System Of units.
With the correct use of molality, know the exact concentration of a certain substance, as well as it will also be possible to establish what is the mass of the solvent, which is extremely necessary to be able to understand the masses of both substances (solute and solvent) and their molalities.
The preparation system to determine the molality of substances is not usually as complex as that of molarity, because it is not necessary to use a volumetric flask, but rather, with the use of a beaker and an analytical balance. it will be enough to carry out the experiment.
Molality has advantages over molarity, because thanks to its methods it is not dependent on affecting factors such as temperature and pressure, because it is not based mainly on volume calculations in the substances studied.
Molality (Concentration)
Molality is defined as the concentration of a solution, clearly speaking in chemical terms, which refers to the relationship or proportion that can exist between two substances, known in this medium as the solute and the solution, or component to be dissolved.
Molality is also known as a term used to indicate that a concentration is being carried out, which involves increasing the proportion of a solute in a solvent, while the opposite process is known as dilution.
For a better understanding of this process, the substance called solute is one that dissolves, while the solvent is all that substance capable of dissolving others. In turn, the dissolution is the result of the homogeneous mixture that was made previously with the two aforementioned substances.
While there is less amount of solute in the mixture, the lower the concentration, and when we speak of a greater amount of solute in the solvent, the concentration would be more proportionate, which implies that a solution is nothing more than a homogeneous mixture between possibly two or more substances.
Solubility
This is a term used to establish the maximum amount of solute that can exist in a solvent, which is totally dependent on some factors such as temperature or pressure that the environment or the same components may present, as well as other previously dissolved substances. or that are in a state of suspension.
This is because there is a certain amount in which the solute can no longer be dissolved by the solvent, and when this happens it is determined that a substance is fully saturated, an example of this could be when a teaspoon of sugar is added to it. a glass of water, if the content is shaken it will be possible to observe how the sugar dissolves, but if the substance continues to be added it will be observed how the sugar will stop dissolving and will remain floating in the water, until a point where it reaches the bottom of the glass. This process can be carried out again if the temperature is changed, for example by heating the water, because this process can be altered with the temperature factor, of course to a certain point, and if the water is cooled, the result will be the possibility of less sugar dissolving in the water.
What are the ways to express molality?
Two basic ways to measure concentration (molality) in substances, which are quantitative and qualitative, being the first of a numerical nature, which are used when you want to know the exact quantities such as molarity, formality, normality and parts per million, while that the qualitative ones are empirical results, so the quantities of the substances in the solution are not exactly known.
Quantitative concentration
This type of knowledge of the proportions of molality in solutions is used mostly in scientific experiments, as well as in industrial procedures, because they are more precise, since they show the exact amounts of the substances.
For the uses of science, and industries such as pharmacies, among others, the use of qualitative concentrations is not efficient, because they do not provide an exact and determined amount and the substances, because they are empirical and not numerical.
The quantitative solution terms are as follows:
- Normality (N): number of equivalents of solute contained in 1 liter of solution, which can be observed as: Equivalence of solute / liters of solution, its property being the volume of the solution.
- Molality: number of moles of solute per kilogram of solvent, which can be observed as: Moles of solute / kilograms of solvent, its property being the weight of solution.
- Molarity: number of moles of solute contained in 1 liter of solvent, which can be seen as: Moles of solute / liters of solution, its property being the volume of solution.
- Weight percent: Weight units of solute contained in 100 weight units of solution, which can be seen as: Grams of solute / 100 grams of solution, its property being the weight of solution.
- Concentration by weight: weight of solute contained in a unit of volume of solution, which can be observed as: Grams of solute / liters of solution, its property being the volume of solution.
The ways of expressing the concentration with these quantitative techniques are the mass-mass or volume-volume percentages, as well as mass-volume, as well as the already known molality, molarity, formality, normality, the molar fraction. When quantities are really small, they are expressed as parts per million, trillion or trillion, being their graphic representations in order as follows: PPM, PPB, PPT.
Qualitative concentration
In this way of determining the amounts of solute in the solvent, numerical techniques are not used so the results are not exact, but rather are known to be empirical, which have a classification depending on the proportion of concentration, as are the following.
Established, saturated and oversaturated
The concentrations of the solutions, or homogeneous mixtures can be classified, of course speaking in terms of solubility, depending on whether the solute is dissolved in the solvent, guided by the amount of it.
- Supersaturated solution: These refer to when a solution contains much more solute than it normally can, that is, it exceeds the allowed limit, this is because the mixtures can be heated, and since the temperature is an affecting factor of the solutions, this can absorb more being under these circumstances, and even when cooled it can continue to contain the same amount as when it was hot, although it can be disturbed even by the slightest movement, changing its composition, and making it a saturated solution.
- Saturated solution: It can be said that a mixture is saturated, when there is an equilibrium between the two substances known as solute and solvent, that is, that the amount of proportion is adequate, so it remains stable without the need to change the temperature pressure factors to be able to complete.
- Unsaturated solution: this type of solution can be distinguished when the solute does not reach the maximum levels of dissolution, so they cannot dilute the solvents with their full capacity.
In other words, it can be said that unsaturated solutions are those that contain the least amount of solute, than they are capable of dissolving, saturated solutions are those that contain the maximum amount of solute that can exist in a solvent, at a certain temperature, and the supersaturated ones are those that contain more than the allowed amount of solute in a solvent, at a given temperature for that occasion.
Diluted or concentrated
These terms are usually used more colloquially because the dilute solutions They can be distinguished by being weak or at relatively low levels, while when we are talking about a concentrated or compound solution it is when the substances are at relatively high levels. It is said relative because these are empirical in nature, so their concentration levels are not known exactly, this can be demonstrated with examples that happen daily in everyday life, such as when you want to make a lemonade you You can see if it is diluted or concentrated by its color or flavor.
In order to understand a little more what these types of solutions imply, the concepts given according to the chemical criteria will be shown below, which are the following.
- Diluted solution: It is one in which the solute can be appreciated in really low proportions in certain volumes given for the occasion.
- Concentrated solution: are those in which the amount of solute can be appreciated a little better, since they are more considerable.
Alternate ways of knowing concentration
There are some solutions that are very common for some branches of science and research for which some alternative or different methods need to be used, due to certain aspects, among which the following can be mentioned.
Baumé scale
This is a scale that was specially designed by the pharmacist and at the same time chemist Antoine Baumé in approximately 1768, close to the date on which he managed to build his aerometer, which he created with the intention of measuring the concentration of some substances such as acids and syrups, the characteristic elements of this scale being the Baumé degrees, which are usually represented by a B or by Bé.
Brix scale
This scale uses as main element Brix degrees, which are usually symbolized with Bx, and their main function is to determine the amount of sucrose in a solution, that is, the amount of sugar that can be dissolved in any type of liquid.
In order to determine the level of sucrose in a liquid, a special instrument called a saccharimeter is necessary, which has the ability to measure the density of liquids, for example if a substance has 25 grams of Bx, it means that there are 25 grams of sucrose per 100 grams of liquid.
This is a scale that was created based on the foundations of other scales capable of measuring the molality (concentration) of solutions, such as the Balling or Plato scale, the Brix being characteristic of sweet substances, such as juice juices. fruits, fruit wines and any substance that resembles them.
Density
Exactly it cannot be said that density is a way of deciphering the concentration of substances, although it has characteristics proportional to that of concentration, as long as they are under the same pressure and temperature conditions, due to this it can be seen that in certain circumstances the density of the solutions is usually said instead of the concentration.
The use of density is not very practical, and it is usually applied to very wide solutions, as well as some tables of conversion of density to molality (concentration) can be mentioned although these techniques are no longer used very frequently.
Definitions of percentages used in these procedures
The most common percentages that can be used to carry out some of the exercises to determine the concentration of the solutions are those of mass-mass, volume-volume and mass-volume, each having its own characteristics.
Volume-volume percentage
With this it is possible to know and express the amounts of solute volume that may exist for every one hundred volume units of the solution, the volume is a very important parameter in this type of solutions, because these are usually composed of liquid or gaseous substances. This means that the amount of volume of total solute refers to the whole amount of volume of solution.
Mass-mass percentage
This is very easily defined, since this percentage wants to express the amount of solute mass, for every hundred mass units in the solution, to understand a little better, if you put 20 grams of salt in 80 grams of water, you will get 20% of the total amount of solute in the solution.
Mass-volume percentage
In this percentage, its elements can be used to obtain a result of what the density of the solution would be, although it is not highly recommended to interlace the procedures, because in most cases it causes confusion to the performers.
The concentration (molality) is the mass of solute, divided by the volume of the solution per hundred units, while the density is the volume of the solution divided by its mass, for this type of procedures they are usually expressed in grams per milliliters (g / ml)
In order to correctly perform the calculations of these percentages, the following two definitions must be taken into account, in order to achieve a perfect or at least effective management.
- The rule of three will always be used as the main tool to perform the calculations of the aforementioned proportions.
- In all cases the sum of the mass of the solute plus the mass of the solvent is equal to the mass of the solution, this means that the solution is equal to the sum of the solute and the solvent.
Normal
This is represented by the letter N and is defined as the number of solute equivalents, between the volume of the solution in liters, to represent the equivalents the letters eq-g are used, the solute the acronym sto, while the liters are used. represented graphically with a capital L.
It should be noted the existence of Redox Normality, which is usually used as a reaction to an antioxidant agent or a reducing agent.
Molarity
It is known as the molar concentration It is represented graphically with the capital M, it is defined as the determination of the amount of solute substance for each liter of solution.
This is the most common method in chemistry that is used to determine the concentrations of substances, and even more so when working with stoichiometric relationships and chemical reactions, although a problem can usually be found during this process, which is the temperature applied to substances, which is usually constant.
Formality
This is known as the molecular mass or more technically as the weight-formula-gram number that can be found relatively in a solution, this is usually represented graphically with the signs g7PFG.
And as the last of these we have Molality, which, as is already known, is the number of moles of solute that each kilogram of solvent contains.
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