For a long time, substances with special characteristics that are of great practical interest have been known and used, which are currently known as acids and bases, which are defined as very common chemical reagents, to which a large part can be developed. of its chemical compounds in aqueous media.
There are some reactions involving acids and bases, called acid-base, which in order to study them, the principles of chemical equilibrium must be applied to solutions, in this type of reactions there is a substance that plays a very important role, which is called solvent, since acids and bases they usually exchange protons with it, thanks to this these can also be called proton exchange reactions.
In ancient times it was already known that some foods such as vinegar and lemon have a characteristic acid taste, although it was not until a few centuries ago that I knew the reason for its peculiar flavor. The word acid actually comes from the ancient Latin language, exactly from its term "acidus" which translates as sour.
What are acids?
This is called as any chemical compound that when going through a dissolution process in water produces a solution with a hydronium cation activity greater than the same water in its purest state, in this situation a pH lower than 7 is presented.
Any chemical substance that possesses the properties of an acid is called acidic substances.
Characteristics of acids
Among the most important properties and characteristics of acids are the following.
- They have the quality of reacting with substances called bases, in order to form salt plus water.
- They are extremely corrosive due to their components.
- They work as excellent conductors of electricity in humid or aqueous environments.
- They have a peculiar sour or sour tasteAn example of this could be foods that contain citric acid such as oranges, limes, grapefruits, lemon, among others.
- They can react with metal oxides to form salt plus water, just like the reaction they do with base substances.
- In some cases they can be harmful, and even cause skin burns.
- It has the ability to generate salt and hydrogen through a reaction process with active metals.
- It has qualities that make phenolphthalein, and in turn can cause litmus paper to change colors, for example from orange to red, and from blue to pink.
What are the Bases?
This is also known as alkali, whose origin is from the Arabic language, exactly from the word "Al-Qaly", they are called as all those substances that possess alkaline properties, although it can also be determined as any solution that, when subjected to an aqueous solution, presents ions to the medium.
Characteristics of the bases
Boyle determined that these substances are all those that possess the following properties.
- To the touch it can be noted that they are soapy in nature.
- They are characterized by their distinguished bitter taste.
- They have the ability to react with acids, in order to generate salt and more water.
- They can turn litmus paper from red to blue.
- They are soluble in water, especially when it comes to hydroxides.
- The vast majority of these so-called base substances are harmful to human skin, because they have characteristics that damage tissues.
Although Boyle and other great chemists tried several times to explain why acids and bases behave in such a way, the first definition of acids and bases was not accepted until 200 years later.
Acid-base reactions
Also known as the neutralization reaction, it is termed as a chemical reaction that happens between an acid and a base that results in salt and water. It should be noted that the word salt describes any compound that has ionic characteristics, whose cation comes from a certain base.
All the neutralization reactions, in which there must always be the presence of acids and bases, they are in most cases exothermic, which means that they release energy in their processes, this reaction is called neutralizing because when an acid is combined with a base , these neutralize each other, leaving their properties null.
Acid-base reaction practice
To start with a neutralizing reaction process, it is necessary to have an Erlenmeyer flask, in which a hydrochloric acid solution is placed, and in turn a few drops of phenolphthalein indicator are added, it turns pink in a base medium, but when It is found in an acidic medium and does not present any color, so it is colorless.
Acid and base neutralizers are produced equally, that is, "equivalent-equivalent", this means that an equivalent of acid will always be completely neutralized by an equivalent of any type of base.
After the previous process, a sodium hydroxide solution is placed in a burette and then cautiously and slowly open the tap, when it is falling little by little, it will react with the hydrochloric acid to form water and chloride. of sodium, This has the effect that the PH increases, and the acid levels decrease.
Once all the acid has been used up, the next drop of base is added to a basic solution, with the effect that the indicator turns pink, this serves to realize that the acid has been completely neutralized.
Generally, the mass of a gram equivalent is determined taking into account the type of substance, this is because the substances are different, each one having its own characteristics, for example the calculation of a salt is not the same as that of a acid, also considering the type of reaction that is being carried out, since depending on the type of reaction the dimensions of the substances are different, so the calculations cannot be reused.
The molar mass of an acid divided by the number of hydrogens that can be dissociated from it is equal to the mass of one gram equivalent of a given acid.
The most common type of base among all those that exist is hydroxide, and its gram equivalent is determined by dividing its molar mass by the number of OH groups in the hydroxide.
The volume of these reactions is calculated by means of a formula, which allows to neutralize a given acid of a base is this: Nto * Vto = Nb* Va, the first being the properties of the acid and the remaining the properties of the base.
In order to calculate the normality of a solution of an acid, one has to proceed as follows: normality = molarity.
Importance of the acid-base reaction
They have a very relevant importance in terms of their ability as techniques for quantitative analysis of volumes, whose processes are determined as acid-base titrations.
To perform these reactions an indicator solution is usually used, which serve as a guide to know the neutralization point, and how it develops, although there are also some electrochemical processes to perform certain tasks.
Three types of reactions can be shown that are divided based on the characteristics of acids and bases, especially on whether they are weak or strong, such as the following.
Reaction of a weak acid and base
In these it can be seen that the cation of the base, and the anion of the acid undergo hydrolysis, so their PH is equal to> 7 if the acid is weaker, and if the base is weaker it is <7.
Reaction between a strong base and a weak acid
In this case, it can be seen how only the anion of the acid undergoes hydrolysis, so its PH remains at <7.
Reaction between a weak base and a strong acid
In this type of reaction, it is only observed how the base cation undergoes hydrolysis, so the PH in it remains> 7.
In order to choose which is the perfect indicator for each type of reaction, it is necessary to know how the final PH will be, in order to correctly calculate the equivalence point.
Historical definitions of the acid-base reaction
There were many definitions of this reaction process between acids and bases, the importance of the same is shown according to the capacity of analysis that each one contains, and more when it is applied to neutralizing reactions with liquid or gaseous substances, or when the characters and properties of acids and bases are usually less evident. .
Definition of Antoine Lavoisier
Lavoisier's knowledge was restricted to strong acids at first, as they were more specific to oxacids which have a high oxidation state in their central atoms, which in turn were surrounded by oxygen atoms, however He did not have full knowledge of the acidic acids, he managed to establish the acids by determining them as the oxygen content, for this he had to use the ancient Greek to name this acid builder.
This theory or definition was ranked as the most important for an incredible 30 years, however in 1810 an article was published that demonstrated some contradictions with bases and foundations, which made Lavoisier's definition lose credibility.
Bronsted-Lowry definition
This definition was formulated independently in 1923, whose bases can be noticed in the protonation of the bases, through the deprotonation process of acids, which can be defined for greater understanding as the ability of acids to be able to donate hydrogen cations to bases, who proceed to accept this procedure.
This has a great difference with the Arrhenius definition, because it does not consist in the formation of water and salt, but rather in that of conjugated acids and bases, which are achieved by the transfer of a proton that can make an acid to deliver it to a base.
In this definition, a drastic change can be observed in the terms with which acids and bases are known, because an acid is known as a compound that has the ability to donate a proton, while bases are all those substances enabled to receive the proton, as a consequence of this, it can be said that an acid-base reaction is the elimination of a hydrogen cation from the acid, and by default the addition of this to the base.
This process wants to refer to the elimination of a proton from the nucleus of an atom, this process is not very easy to achieve, since the simple dissociation of acids is not enough, but rather it is necessary to proceed with the elimination of a cation hydrogen.
Lewis definition
This definition includes the foundations of the Bronsted-Lowry theory as well as the concept that this proposed for the solvent system, this theory was postulated in 1923 by the chemist Gilbert Lewis.
Lewis in this definition proposes a base, which he named "the Lewis base" which has the ability to donate an electronic pair and acids as "Lewis acid" being this the respective receptor of said electronic pair. This definition is completely different from those proposed and postulated above, because they do not mention that acids and bases are measured with protons or some bound substance.
This supposed in his theory that the anion was the acid, and the cation was the base that has a non-shared electronic pair, if this definition is used, the acid-base reaction could be understood as the direct donation of an electronic pair comes from of the anion, delivering it to the cation, managing to form a coordinated covalent bond. This combination is known as the formation of the most vital compound for life, water.
Definition of Liebig
This was proposed in 1828, a few decades later than Lavoisier's, this theory was based on his extensive work on the chemical composition of organic acids. Before this definition there was a doctrinal distinction which was initiated by Davy, which focused more than anything on acids based on oxygen, and acids based on hydrogen.
According to Liebig an acid can be defined as a substance that contains in itself hydrogen, and that can even be replaced, or changed by a metal. This theory despite being based mostly on empirical methods, managed to be in force for 5 decades.
Definition of Arrhenius
The Swedish chemist Svante Arrhenius sought to modernize the terms and definitions that had been given to the reaction that occurred between acids and bases, in turn seeking to simplify the terms of this.
In 1884 he carried out a joint work with Friedrich Wilhelm in which they managed to establish the presence of ions in an aqueous solution, due to the importance of a certain work Arrhenius was granted the prodigious opportunity to receive a Nobel Prize in chemistry in the year 1903.
The traditional definition of aqueous acid-base can be described as the peculiar formation of the component known as water from hydroxyl and hydrogen ions, or also as the formation of these from the dissociation of acids and a base in aqueous solution.
Pearson's definition (hard-soft)
This definition postulated by Ralph Pearson in 1963 although it was developed more strongly in 1984 with the support of the work of Robert Parr, whose name is the reaction acid-base hard-soft, these adjectives are used as follows, Soft is used to refer to the larger spices, which have low oxidation states, and they are strongly polarized, Hard is used to refer to the smallest species, and they are characterized by having higher oxidation states.
This definition has been very useful for the processes of organic and inorganic chemistry, and its main practices indicate that acids and bases can interact with each other, and the most common are the reactions of compounds that have the same traits, such as for example soft-soft, or hard-hard.
This theory is also known as the ABDB definition, which is very useful for predicting the products of metathesis reactions. Today it has been proven that this reaction can demonstrate the sensitivity and performance of explosive materials.
This theory is based more on qualitative characteristics than quantitative ones, which help to understand in a simpler way the predominant factors of chemistry and reactions.
Definition of Usanovich
Mikhail Usanovich, a Russian chemist, also made a definition of what the acid-base reaction implies, and it can be said that this is the most generalized of all, in which it is determined that acids are all those chemical substances that are capable of accept negative species, or that, failing that, donates positive species, the concept of the base being given by Usanovich, the opposite of those of acids.
The reaction of acids and bases proposed by this Russian chemist coincides with another chemical reaction, known as the "redox reaction" which involves an oxidation-reduction reaction, so it is not favored by chemists.
Most of the proposed reactions are based on bond formation and breaking, but redox and Usanovich's are set more like physical electronic transfer processes, which causes the distinction between these two to be totally diffuse.
Definition of Lux-Flood
This definition is generally used in modern geochemistry and electrochemistry of molten salts, whose postulation was made in 1939 by a German chemist known as Hermann Lux, and was developed again achieving a significant improvement in 1947 by the chemist Hakon Flood, for this reason is known to this reaction by the two surnames of the same ones.
In this we can see very peculiar concepts of acids and bases, the base being a donor of oxide anions, while acids are the recipients of said anions.
Definition of solvent system
This definition is very important to know in relation to this issue, since several of the chemists who have carried out their theories over the years have sometimes commented on the solvent system, which is based on a generalization of the Arrhenius definition. exposed above.
There is a certain amount of positive species in most of these solvents, known as solvonium cations, and failing that, they also have negative species such as solvonium anions, which are in a state of equilibrium with the neutral molecules of the solvent.
In this definition, the base can be described as a solute that causes an increase in the concentration of solvonium cations, while the acids are those that cause a decrease in the solvonium anions.
This definition depends on both the compound and the solvent, so depending on the solvent chosen, the compound may have the ability to change its own behavior.
It is very interesting how the different chemists from different parts of the world, and different times, each spoke and proposed a different definition on the same topic, and in turn this is very important for the study and history of chemistry, because putting together With all these terms, it has been possible to know even better all the aspects considered about acids and bases and their neutralizing reactions.
I am poorly educated and with little knowledge in chemical science but even so, I have a doubt with the phrase "the elimination of a hydrogen cation" that apparently in the text is opposed to the concept "PROTON" as something different, which probably thus In other words, but apart from technicalities, yes to an H atom that I think has a single electron, this is removed, what remains is obviously a proton, so for example, we talk about a proton pump that I understand that generates acidity in the stomach .
In any case, this article is very good.