Theory According to Bronsted-Lowry
Acids are donor protons, while bases are proton acceptors.
The acid-base theory from Arrhenius apparently cannot apply to all solvents, because it is specifically for water solvents. Likewise it is not suitable with the salting reaction because not all salts are neutral, but some are acidic and some are alkaline.
The concept of acid base is more commonly proposed by Johannes Bronsted, base is a substance that can receive protons. Ionization of hydrochloric acid in water is seen as the transfer of protons from acids to bases.
HCl + H 2 O -> H 3 O + + Cl -
Likewise the reaction between hydrochloric acid and ammonia, involves the transfer of protons from HCl to NH 3.
HCl + NH 3 ⇄ NH 4 + + Cl -
Ionization of weak acids can be described in the same way.
HOAc + H 2 O ⇄ H 3 O + + OAc -
In 1923 a British chemist named T.M. Lowry also proposed the same thing with Bronsted so his acid-base theory was called Bronsted-Lowry. It should be noted here that H + from acids combine with water molecules to form polyatomic ions H 3 O + called Hydronium ions. Common reactions that occur when acid is dissolved in water are:
HA + H 2 O ⇄ H 3 O + + A -
This presentation shows the great role of polar water molecules in attracting protons from acids.
Note that conjugate acids are formed if the proton still remains after the acid has lost one proton. Both are conjugate acid-base pairs consisting of two substances that are related to each other because of the proton administration or proton reception. However, acid-base dissociation is still used in Arrhenius, but the true meaning we must understand
Johannes N. Bronsted and Thomas M. Lowry prove that not all acids contain H + ions and not all bases contain OH - ions.
Bronsted - Lowry put forward the theory that acids are species that give H + (donor protons) and bases are species that accept H + (proton acceptors). If an acid gives an H + to a base molecule, then the rest will be the conjugate base of the original acid. Likewise, if the base receives H +, then the rest is the conjugate acid from the original base. Bronsted - Lowry's theory clearly shows the presence of Hydronium ions (H 3 O +) significantly.
HF is a pair of F - and H 2 O is a pair of H 3 O +. Water has ampiprotic properties because it can be as a base and can be as an acid.
HCl + H 2 O -> H 3 O + + Cl -
Alkaline Acid
NH 3 + H 2 O ⇄ NH 4 + + OH -
The benefits of the acid-base theory according to Bronsted - Lowry are as follows:
1. The application is not limited to water solvents, but to all solvents containing Hydrogen atoms and even without solvents.
2. Acids and bases are not only molecular, but can also be anions and cations.
Another example:
HAc (aq) + H 2 O (l) -> H 3 O + (aq) + Ac - (aq)
acid-1 base-2 acid-2 base-1
HAc with Ac - is a conjugate acid-base pair.
H 3 O + with H 2 O is the conjugate acid-base pair.
H 2 O (l) + NH 3 (aq) -> NH 4 + (aq) + OH - (aq)
acid-1 base-2 acid-2 base-1
H 2 O with OH - is a conjugate acid-base pair. NH 4 + with NH 3 is the conjugate acid-base pair.
In the example above it appears that water can be both acidic (donor proton) and basic (proton acceptor). Substances or ions or species like this are ampiprotic (amphoteric).