A acid is a substance that is capable of releasing ions of hydrogen (H+) in a solution. However, an acid is also considered a substance that can receive a pair of electrons.
Refering to base, This is considered as a substance capable of dissociating ions of hydroxide (OH-) in a solution. In addition, substances capable of donating a pair of electrons are also considered..
Both acids and bases can be identified according to their position on the pH scale. In the case of acids, these have a value lower than 7, while bases (alkalines) have a value higher than 7.
| Acid | Base | |
|---|---|---|
| Definition | An acid is a substance that is capable of releasing hydrogen ions H+ in solution. | A base is a substance capable of dissociating OH hydroxide ions- in a solution. |
| Arrhenius theory | It is a substance that releases hydrogen ions H+ in aqueous solution. | It is a substance that dissociates a hydroxide anion OH- in an aqueous medium. |
| Brønsted-Lowry theory | They are substances with the ability to donate or give up protons (hydrogen atoms without their negative electron: H+). | It is a substance capable of accepting protons (H+) in solution. |
| Lewis theory | It is a substance capable of accepting a pair of electrons. | It is a substance that has the ability to donate or give electrons. |
| Properties |
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| PH level | Less than 7. | Greater than 7. |
| Examples |
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An acid is a substance capable of releasing hydrogen ions in a solution. In addition, a compound that can receive a pair of electrons is also considered as acid..
The word "acid" comes from the Latin acidus, which means 'sour' or 'sharp', and refers to the unpleasant taste of certain substances (for example, vinegar).
Acids can be considered strong or weak depending on how they dissociate in an aqueous medium, that is, according to the amount of hydrogen ions they release in a solution.
An acid is strong when it is easily ionized, that is, the vast majority of its hydrogen ions or protons are given up in solution. These acids are highly corrosive and good electrical conductors..
Examples of strong acids are sulfuric acid HtwoSW4, hydrobromic acid (HBr) and hydrochloric acid (HCl).
In contrast, acids weak They are those that do not release a large amount of hydrogen ions and are less corrosive than strong acids. Examples of weak acids are carbonic acid (HtwoCO3) and acetylsalicylic acid (C9H8OR4).
Discover other characteristics of acids and bases.
A base is a substance capable of dissociating hydroxide ions in a solution, having a pH greater than 7. A substance capable of donating a pair of electrons is also considered as a base, and includes all alkaline solutions.
The word "base" comes from the Greek basis and means 'to go' or 'to walk', while "alkaline" comes from the Latin alkali, which in turn comes from the Arabic Al-Qali, y means 'ashes', particularly those from burned wood.
Strong bases ionize completely, yielding their hydroxide ions to solution. Examples of strong bases are lithium hydroxide (LiOH), potassium hydroxide (KOH), and sodium hydroxide (NaOH)..
As for the weak bases, these are those that partially dissociate. Examples of weak bases are ammonia (NH3) and sodium bicarbonate (NaHCO3).
Get more examples of acids and bases here.
Historically, these substances have been studied based on their properties and interactions with other elements. There are various theories that explain these phenomena and that are still in force..
Some of the best known, and which will be presented below, are the acid-base theory of Arrhenius (derived from his theory of electrolytic dissociation) of 1887, the acid-base theory of Brønsted-Lowry (which presents the notion of conjugated acid-base pairs) of 1923, and the Lewis theory (in which the reception and donation of electrons is fundamental).
According to the Swedish chemist Svante August Arrhenius (1859-1927), an acid is a substance that releases hydrogen ions H+ in an aqueous solution (water).
In the theory of electrolytic dissociation of Arrhenius (1887), acids are compounds that have hydrogen and that, when dissolved in a aqueous medium, release hydrogen ions (protons) or hydronium (H3OR+ protons surrounded by water molecules). In this case, electrolytes (anions or cations) are capable of conducting electrical charges..
For its part, the base is a substance that dissociates a negatively charged ion (anion) hydroxide (OH-) in an aqueous medium.
The Arrhenius definition has the limitation that it does not consider reactions in which there is no aqueous solution, nor those basic compounds that do not release hydroxide..
Acid: hydrochloric acid or HCI → CI-(aq) + H+(aq)
Base: sodium hydroxide or NaOH → Na+(aq) + OH-(aq)
The Danish scientist Johannes Nicolaus Brønsted (1879-1947) and the English scientist Thomas Martin Lowry (1874-1936) published studies (1923) in which acids are defined as substances with the ability to donate or give protons (hydrogen ions H+ without their negative electron) to another that must accept them. As for the base, this is a substance capable of accept protons (H+) in solution.
Within this theory, acids are not restricted to dissolution in water, other solvents are also included.
Thus, this definition expands the one presented by Arrhenius, in which an acid was limited to a substance that releases hydrogen ions in an aqueous medium. That is, an acid is a substance that donates protons to another substance, while a base accepts them from another substance..
With the Brønsted-Lowry theory, the notion of conjugated acid-base pairs is introduced, by a proton transfer, in which the acid donates them and the base accepts them. In this case, acid and base coexist, since an acid can only act in the presence of a base and vice versa..
When an acid donates a proton, this acid is called conjugate base. The same thing happens, on the contrary, when a base receives a proton. This base is known as conjugated acid.
This happens because the acid becomes a conjugate base by donating a proton, that is, a substance that is capable of accepting a proton. In the case of the base, when it accepts a proton, it becomes a substance capable of giving up a proton.
A neutralization reaction occurs when an acid and a base produce water and a salt.
Hydrochloric acid and ammonia:
HCl (is the acid) + NH3 (is the base) ⇋ NH4+ (is the conjugated acid) + Cl- (is the conjugate base)
The American scientist Gilbert Lewis (1875-1946), proposed a theory at the same height (1923) in which the Brønsted-Lowry theory was presented. For this scientist, an acid is a substance capable of to accept a pair of electrons.
This definition of acid includes all Brønsted-Lowry acids, since hydrogen ions (protons) are electron receptors, and it encompasses many other substances that do not contain hydrogen..
In Lewis theory, bases are substances that have the ability to donate a pair of electrons.
By including Brønsted-Lowry acids and bases (proton donors and receptors, respectively), the Lewis theory also incorporates Arrhenius acids and bases (hydrogen and hydroxide ions that react in an aqueous medium).
Ammonia and boron trifluoride:
BF3 (is the acid) + NH3 (is the base) → H3N - BF3
Also know the Difference between organic and inorganic compounds.
PH is the hydrogen potential of a solution, devised by the Danish scientist Søren Peder Lauritz Sørensen (1868-1939) in 1909. It indicates the concentration of hydrogen ions in a substance. To represent this concentration, a scale is used that indicates the level of alkalinity or acidity of a solution..
This scale is quantified from 0 to 14. Substances that have a level less than 7 are considered acidic, while substances that have a level greater than 7 are considered bases (alkaline)..
PH scale: pH = -log10 [H+]
Each movement from one point to another on the scale is logarithmic, which means that one step increases or decreases the acidity / basicity 10 times with respect to the step immediately below or above. That is, if the acidity of vinegar is pH 3, the acidity of lemon juice is 10 times higher, with a pH of 2.
Water has a pH ranging from 6.5 to 8.5, where the pH of the pure water is 7 (which is considered neutral). When water has a pH lower than 6.5, it can have toxic metals in its composition, being corrosive and acidic. When its pH is higher than 8.5, it is called hard water, more basic or alkaline, with a higher presence of magnesium and carbonates.
It may interest you Strong and weak acids and bases.
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