CK-12-Chemistry Intermediate

http://www.ck12.org Chapter 21. Acids and Bases

This is merely a simplification of the previous equation, but it is commonly used. Any hydrogen ions in an aqueous
solution will be attached to water molecules as hydronium ions.

Not all hydrogen atoms in molecular compounds are ionizable. In methane (CH 4 ), the hydrogen atoms are covalently
bonded to carbon in bonds that are only slightly polar. The hydrogen atoms are not capable of ionizing, and methane
has no acidic properties. Acetic acid (CH 3 COOH) (Figure21.3) belongs to a class of acids called organic acids.
There are four hydrogen atoms in the molecule, but only the one hydrogen that is bonded to an oxygen atom is
ionizable.

FIGURE 21.3

The O-H bond can be ionized to yield the H+ion and the acetate ion. The

other hydrogen atoms in this molecule are not acidic.

TheTable21.1 lists some of the more common acids. Recall that the rules for naming acids were covered in the
chapterChemical Nomenclature.

TABLE21.1: Common Acids

Acid Name Formula

Hydrochloric acid HCl

Nitric acid HNO 3

Sulfuric acid H 2 SO 4

Phosphoric acid H 3 PO 4

Acetic acid CH 3 COOH

Hypochlorous acid HClO

Amonoprotic acidis an acid that contains only one ionizable hydrogen. Hydrochloric acid and acetic acid are
monoprotic acids. Apolyprotic acidis an acid that contains multiple ionizable hydrogens. Most common polyprotic
acids are either diprotic (such as H 2 SO 4 ) or triprotic (such as H 3 PO 4 ).

Arrhenius Bases

Bases are ionic compounds which yield the hydroxide ion (OH−) upon dissociating in water. TheTable21.2 lists
several of the more common bases.

TABLE21.2: Common Bases

Base Name Formula

Sodium hydroxide NaOH

Potassium hydroxide KOH

Magnesium hydroxide Mg(OH) 2

Calcium hydroxide Ca(OH) 2

All of the bases listed in the table are solids at room temperature. Upon dissolving in water, each dissociates into a
metal cation and the hydroxide ion.