Taking an antacid for acid reflux, heartburn or indigestion helps to relieve the burning sensations and the pain. An antacid, containing a base like calcium carbonate or magnesium hydroxide, relieves pain by neutralizing stomach acid. A reaction between an acid and a base is called neutralization.
Acid and Base Definition and Examples
An acid is a chemical species that donates hydrogen ions, H+, in an aqueous solution; it loses a proton. A base creates hydroxide ions, OH-, in an aqueous solution; it gains a proton.
An acid-base reaction will produce water and a salt. In the above reaction, the salt sodium chloride will form. Note that the salt product of a neutralizing reaction has a broader meaning than table salt, sodium chloride. It refers to a compound with two parts adhering to each other through an ionic bond.
Besides antacids, other examples of neutralization reactions are used in first aid. Both acids and bases can cause burns, and if a solution comes into contact with skin, the opposite could be applied to neutralize the effect. For example, the base baking soda (NaHCO3) can be used on acid burns or the acid vinegar (CH3COOH) can treat lye.
Acid-Base Reaction Equations
The general equation for an acid-base reaction is:
acid + base = salt + water
The chemical equation for the hydrochloric acid and sodium hydroxide reaction is:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
The ionic equation of the above reaction is:
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) → Na+(aq) + Cl-(aq) + H2O(l)
Notice that the chlorine and sodium ions are found on both sides of the equation, and the net ionic equation is:
H+(aq) + OH-(aq) → H2O(l)
All reactions between a strong base and strong acid neutralize to this equation. Note that this reaction complies with the definitions of acids and bases; the presence of H+ and OH- are in aqueous solution. The acid loses the H+ ion, and it is transferred to the base.
The reaction of an acid and base of equal magnitude will result in a pH equal to 7, a neutral solution. If a strong acid, like hydrochloric acid, and a strong base, like sodium hydroxide, are reacted, a neutral solution will result.
Neutralization Reaction and Equivalents
In a neutralization reaction, equivalent amounts of acid and base combine to form equivalent amounts of salt and water. An equivalent is the reactive capacity of a chemical species.
In acids, the equivalent unit is the number of hydrogen ions (H+) provided for a reaction. In hydrochloric acid, HCl, the equivalent is 1, and in sulfuric acid, H2SO4, it is 2.
In bases, the equivalent is the number of hydroxide ions (OH-) provided for a reaction. In sodium hydroxide, NaOH, the equivalent is one, and in barium hydroxide Ba(OH)2 it is two.
One equivalent of an acid reacts with one equivalent of a base. The acid HCl and the base NaOH, both with one equivalent, have the same reactivity. If H2SO4, with two equivalents, reacts with NaOH, with one equivalent, it will take twice the amount of the NaOH to react with the sulfuric acid.
Neutralization Reactions: Titrations
In the chemistry laboratory, acid-base reactions are commonly completed through a process called titration. A solution of known concentration is carefully added into one of unknown concentration.
An indicator, like phenolphthalein, is added into the unknown concentration. When the solution changes color (such as colorless to pink), the titration or neutralization point has been reached, and the unknown concentration may be calculated.