Neutralization Reactions. Total and Partial Neutralization

Neutralization reactions occur when we mix an acid and a base so that the pH of the medium is neutralized and water and a salt are produced.

The acid releases H cations in the medium⁺ that bind to OH anions^- released by the base and, with that, water molecules are formed. Salt is formed by the union of the anion of the acid with the cation of the base.

Generically, we have:

HA + Boh → H₂O + BA
 ^{ACID BASE WATER SALT}

To understand how the medium is neutralized, think, for example, of a beaker containing nitric acid, which has a pH of approximately 2.0. Let's say that we are gradually adding milk of magnesia to the acid. Milk of magnesia is a solution of magnesium hydroxide base, which has a pH of approximately 10.0.

The higher the pH of a solution, the more basic it will be, and vice versa.

Over time, the pH of nitric acid will increase, meaning it is being neutralized by the milk of magnesia. There will come a point when the pH of the medium will reach the value equal to 7.0, which is the pH of water. We say, then, that the medium is neutral.

This is a reaction of total neutralization, which can be expressed by the following chemical equation:

2 hoursAT THE₃ + mg(OH)₂ → 2 hours₂O + Mg (NO₃)₂
^{ACID BASE WATER SALT NEUTRAL}

A full neutralization reaction occurs when the amount of H ions⁺ released by the acid is equal to the amount of OH ions^- released by the base.In the case of the example above, two H were released⁺ and two oh^-.

However, reactions of partial neutralization, that is, in which the amount of H ions⁺ and oh^- released by acid and base, respectively, is different.

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Partial neutralization can take place in two ways:

1. With the formation of a salt with an acidic character:

Here's an example: While each phosphoric acid formula releases three H⁺, each molecule of sodium hydroxide base releases only one OH^-. Thus, not all of the ionizable hydrogens in the acid are neutralized by the hydroxyls in the base. The result is the formation of a acid salt, also called hydrogen salt:

H₃DUST₄ + Inoh → H₂O  + InH₂DUST₄
^{ACID BASE WATER SAL ACID}

2. With formation of a salt with a basic character:

Here, the opposite of the previous case occurs, as the base releases more hydroxyls than the acid releases ionizable hydrogens. In this way, the salt produced will be a basic salt or hydroxysalt.

Example: Hydrochloric acid releases only one H cation⁺, while magnesium hydroxide releases two OH^-_. In this way, a hydroxyl will remain without being neutralized:

HCl + Mg(OH)₂ → H₂O + mg(OH)Cl
^{BASIC ACID WATER BASED SALT}

This is exactly the reaction that occurs in our stomach when we have heartburn and take an antacid. The main component of gastric juice is hydrochloric acid (HCl), some factors such as food, nervous tension and illness can increase the amount of HCl in our stomach, giving that feeling of burning. To neutralize this acidic environment, stomach antacids such as milk of magnesia (Mg(OH)₂), can be taken under medical advice. In this way, excess stomach acidity will be neutralized.

By Jennifer Fogaça
Graduated in Chemistry

Would you like to reference this text in a school or academic work? Look:

FOGAÇA, Jennifer Rocha Vargas. "Neutralizing Reactions"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/reacoes-neutralizacao.htm. Accessed on June 28, 2021.

b) Equate partial H neutralization reactions₃DUST₄ with aqueous potassium hydroxide (KOH) solution.