Acid-base reactions, also known as neutralization reactions, are important in biochemistry as well as industrial chemistry. Furthermore, many of the compounds we come into contact with in our daily life are acids or bases. Aspirin, for example, is an acid (acetylsalicylic acid), whereas antacids are bases. In fact, every home cook who has made mayonnaise or squeezed a lemon wedge to marinade a piece of fish has performed an acid-base reaction.
Acid-base reactions are among the simplest to recognize and comprehend. Second, some types of organic substances have obviously acidic qualities, while others behave as bases, thus we must determine these aspects of their chemistry. Finally, acids and/or bases are typically used as catalysts in organic processes. Although these transformations may appear complicated, our comprehension of how they happen frequently starts with how the catalyst works.
What is acid-base reaction?
The acid-base reaction definition outlines the chemical change that occurs in a reaction between acid and base.
Acids exchange protons for electrons from bases. When a base receives a proton from another molecule, a conjugate acid is created. It is referred to as an acid due to its ability to function. The conjugate base and conjugate acid are the acid-base reaction products. A conjugate base is the chemical created when an acid loses its proton, according to Bronsted-Lowry. It is called a base because it can act as one by reaccepting lost protons.
A hydrogen ion, H+, is transported from one chemical species to another in an acid-base reaction. Such reactions are critical to a wide range of natural and manmade processes, from the chemical transformations that occur within cells and in lakes and oceans to the industrial-scale manufacture of fertilizers, medicines, and other societally important compounds. Although acids and bases have distinct chemistries, their chemistry cancels out to form water.
The general acid-base reaction is,
acid + base ⟶ water + salt
where the ‘salt’ refers to any ionic compound (soluble or insoluble) produced by the interaction of an acid and a base.
What are Acids and Bases?
An acid is any hydrogen-containing substance capable of transferring a proton (hydrogen ion) to another substance.
A base is a molecule or ion that can accept a hydrogen ion from an acid.
Acids dissociate to produce a solution that is enriched in protons H+ and the corresponding conjugate base.
HA ⇋ H+ + A−
Bases dissociate to produce a solution rich in hydroxyl ions OH– and their conjugate acids.
BOH ⇋ B+ + OH−
The conjugate base and conjugate acid are the acid-base reaction products.
The conjugate base of an acid is what remains after the acid has donated a proton. Because it can accept a proton to reform the original acid, this species is base.
The conjugate acid of a base is the product of the base accepting a proton. This species is classified as an acid since it can give up a proton to reform the original base.
Definitions of Acids and Bases
Arrhenius Acid-base reactions: According to the Arrhenius theory, acid-base reactions always create water (along with salt) because H+ ions (produced by acids) and OH– ions (produced by bases) react in an aqueous solution to form water.
An ionic equation of an Arrhenius acid-base reaction:
H+ (aq) + OH− (aq) → H2O (l)
Brønsted-Lowry Acid-base reactions: According to the Brønsted-Lowry theory, acid-base reactions involve the transfer of protons or H+. The dissociation of acid (or base) in water is the best example of this type of reaction. Because it receives a proton from the acid, water behaves as both a solvent and a base in this reaction.
Not all neutralisations result in the formation of water. Consider the following reaction between ammonia (base) and hydrogen chloride (acid):
Lewis Acid-base Reaction: A Lewis acid-base reaction occurs when a Lewis acid reacts with a Lewis base. Lewis acids (also known as electrophiles) receive electrons from Lewis bases (also called a nucleophile). An electrophile “loves electrons” and has an empty orbital that can accommodate the nucleophile lone pair of electrons. The positively charged electrophile is “attacked” by the nucleophile, which provides it with an extra lone pair of electrons.
Boron trifluoride, BF3, is an example of a Lewis acid. Because it contains a vacancy in its octet, it can accept a pair of electrons. The fluoride ion has a complete octet and can contribute two electrons.
Strong Acid and a Strong Base
Strong acids and strong bases both dissociate entirely into their respective ions. This means that the molecules of both acids and bases will separate fully. They reform to form the conjugate acid and conjugate base, which are salt and water.
Complete neutralization of a strong acid and a strong base occurs when the mole quantities of strong acid and strong base are identical. An aqueous solution with a pH of 7 is the end product.
Strong acids and strong bases are listed below
|Strong Acid||Strong Base|
|Hydrobromic acid||HBr||Barium hydroxide||Ba (OH)2|
|Hydrochloric acid||HCl||Calcium hydroxide||Ca (OH)2|
|Hydroiodic acid||HI||Lithium hydroxide||LiOH|
|Nitric acid||HNO3||Potassium hydroxide||KOH|
|Perchloric acid||HClO4||Sodium hydroxide||NaOH|
|Sulfuric acid||H2SO4||Strontium hydroxide||Sr (OH)2|
Weak Acid and Weak Base
The results of a weak acid and a weak base reaction are the same as the products of a strong acid and a strong base reaction. A neutral solution of salt and water is generated when equal amounts of weak acids and weak bases are used.
A weak acid or base dissociates only partially.
Weak acid: HA + H2O ↔ A–(aq) + H3O+(aq)
Weak base: BOH + H2O ↔ B+(aq) + OH–(aq)
If both the acid and the base are weak, the ultimate pH will be determined by their pKa. The pH of a solution might be acidic, basic, or neutral. Due to the limited dissociation of the weak acid and weak base, these reactions frequently fail to complete.
|Weak Acid||Weak Base|
|Hydrocyanic acid||HCN||Sodium bicarbonate||NaHCO3|
Strong Acid and a Weak Base
The conjugate base and conjugate acid are the results of the reaction between a strong acid and a weak base. The products of this specific acid-base interaction have an acidic pH; it is less than 7. This is due to the fact that the effects of the powerful acid are more dominating. This indicates that the final solution will be more acidic.
Weak Acid and a Strong Base
When a precise amount of a weak acid reacts with an equivalent amount of a strong base, a basic solution is created. Because the properties of the strong base are more prevalent, the pH of their products is higher than 7.
Some of Acid-Base Reaction Examples
- HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
- HBr (aq) + KOH (aq) → KBr (aq) + H2O (l)
- HCl (aq) + NH3 (aq) → NH4Cl (aq)
- 2 HCl (aq) + Mg (OH)2 (aq) ⟶ 2 H2O (l) + MgCl2 (aq)
- H2SO4 (aq) + Sr (OH)2 (aq) ⟶ 2 H2O (l) + SrSO4 (aq)
- 2 H3PO4 (aq) + 3 Ca(OH)2 (aq) ⟶ 6 H2O (l) + Ca3(PO4)2 (s)
- 2HCl (aq)+CaCO3 (aq) → CaCl2 (aq) + H2O (l) + CO2 (g)
- HCl (aq)+NaHCO3 (aq) → NaCl (aq) + H2O (l) + CO2 (g)
- Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2000). Organic Chemistry (First ed.). Oxford University Press.
- Finston, H.L.; Rychtman, A.C. (1983). A New View of Current Acid-Base Theories. New York: John Wiley & Sons.
- Meyers, R. (2003). The Basics of Chemistry. Greenwood Press.
- Paik, Seoung-Hey (2015). “Understanding the Relationship Among Arrhenius, Brønsted–Lowry, and Lewis Theories”. Journal of Chemical Education
- Whitten K.W., Galley K.D. and Davis R.E. General Chemistry (4th ed., Saunders 1992)