Definition of Acids and Bases

Candela Rocío Barbisan | Nov. 2021
Chemical engineer

To better understand the idea, we move on with a reaction where H + (proton) are transferred:

HCl_(g)+ H₂OR_(l) → Cl^-_(ac) + H₃OR⁺_(ac)

In this reaction it is seen how hydrogen chloride (HCl) loses an H⁺, obtaining Cl- and said proton is accepted by the Water forming a hydronium ion H₃OR⁺. It is now easy to identify the acid and the base, as the name implies, hydrochloric acid will be the acid while water will act as the base.

Examples

Acid-base reactions are very important both in everyday chemistry and in industry. And perhaps, despite not knowing in depth how these reactions developed, there was a preconception of the acids and bases with which we are usually in contact. Examples include:

- Citrus fruits, characteristic for their "sour" taste, are the most popular acids.

- vinegar, it is made up of acetic acid.

- sodium hydroxide, a strong base used in many industrial processes, famously known as “caustic soda”

- calcium oxide, is the lime that can be bought in hardware stores.

And so we could continue for a long time, since there are thousands of acids and bases that, when combined, give rise to acid-base reactions.

Another typical case is that of vinegar, mentioned above, formed through the dissolution of acetic acid in water, let's see the reaction at play:

HC₂ H₃ OR_2(ac) + H₂OR_(l) ↔ C₂H₃OR₂^-_(ac)+ H₃OR⁺_(ac)

You can identify certain analogy with the reaction of hydrogen chloride, in this case acetic acid loses an H⁺, which is received by water, forming two ionic species, two electrolytes. Any hydrogen atom in an acid that can be donated to a base is known as acidic hydrogen. If we look back at the last reaction we see that only one of the four hydrogens that it has participates in the donation, is the only acidic hydrogen that the compound has. Well, there are compounds that have more than one acidic hydrogen, however, each of them will be more or less easily transferred.

When the compound has a single acidic hydrogen it is said to be monoprotic, and this is the case of acids seen above, both hydrochloric acid and acetic acid are acids monoprotic. But let's look at some diprotic acids as an example, one of the most recognized is sulfuric acid H₂SW₄, who is able to donate his two acidic hydrogens, one of them more easily than the other. In this case, if you only donate an acidic hydrogen it forms HSO₄^-, called hydrogen sulfate, while if you donate two acidic hydrogens it forms SO₄^-2, sulfate, an ion with a negative charge more than the previous one.

As for the bases, the simplest are those that come from ionic compounds, such as hydroxides. Many of them are soluble in water and, when dissolved, are capable of dissociating, for example, we previously spoke of caustic soda or sodium hydroxide:

NaOH_(s) → H₂O Na⁺_(ac)+ OH^-_(ac)

We can easily identify that it is a base, since when it dissociates in water we see hydroxyl ions (OH^-) characteristic. And like sodium hydroxide we can name some more like KOH or Al (OH)₃. Another example is that of ammonia, the base of which can react with water to form the ion hydronium as follows:

NH_3(ac)+ H₂OR_(l) ↔ NH₄⁺_(ac) + OH^-_(ac)

It should be noted that, in the case of NaOH, there is simply a dissociation in water while, in the case of NH₃, hydroxyl ions are produced because there is a chemical reaction, in which the water acts as an acid against the base, donating protons.

To identify acids and bases there are different tests, some can be done at home and others in the laboratory. In a simple way we could take litmus paper and, when put in contact with an acid, it turns to reddish colors, while when put in contact with a base it turns to blue. However, indicators There are acid-base of different prices, qualities and availabilities and their functioning is based on the color change when exposed to a substance acidic or basic and one of the most recognized for its availability and price is phenolphthalein.