Acid-Base Chemical Reaction

Mixing an acid with a base is a common chemical reaction. Here is a look at what happens and the products resulting from the mixture.

Understanding the Acid-Base Chemical Reaction

First, it helps to understand what acids and bases are. Acids are chemicals with a pH less than 7 that can donate a proton or H⁺ ion in a reaction. Bases have a pH greater than 7 and can accept a proton or produce an OH^- ion in a reaction. If you mix equal amounts of a strong acid and a strong base, the two chemicals essentially cancel each other out and produce a salt and water. Mixing equal amounts of a strong acid with a strong base also produces a neutral pH (pH = 7) solution. This is called a neutralization reaction and looks like this:

HA + BOH → BA + H₂O + heat

An example would be the reaction between the strong acid HCl (hydrochloric acid) with the strong base NaOH (sodium hydroxide):

HCl + NaOH → NaCl + H₂O + heat

The salt that is produced is table salt or sodium chloride. Now, if you had more acid than base in this reaction, not all of the acid would react, so the result would be salt, water, and leftover acid, so the solution would still be acidic (pH < 7 ). If you had more base than acid, there would be leftover base and the final solution would be basic (pH > 7).

A similar outcome occurs when one or both of the reactants are 'weak'. A weak acid or weak base doesn't fully break apart (dissociate) in water, so there may be leftover reactants at the end of the reaction, influencing the pH. Also, water may not be formed because most weak bases are not hydroxides (no OH^- available to form water).

Gases and Salts

Sometimes gases are produced. For example, when you mix baking soda (a weak base) with vinegar (a weak acid), you get carbon dioxide. Other gases are flammable, depending on the reactants, and sometimes these gases are flammable, so you should use care when mixing acids and bases, especially if their identity is unknown.

Some salts remain in solution as ions. For example, in water, the reaction between hydrochloric acid and sodium hydroxide really looks like a bunch of ions in aqueous solution:

H⁺(aq) + Cl^-(aq) + Na⁺(aq) + OH^-(aq) → Na⁺(aq) + Cl^-(aq) + H₂O

Other salts are not soluble in water, so they form a solid precipitant. In either case, it's easy to see the acid and base were neutralized.

Test your understanding with an acids and bases quiz.