Acids, Salts, and the Metal Activity Series
Ion charges explain salt formulas, while relative metal activity helps predict selected metal–acid reactions.
1. Acids and their ions
In water, acids increase the concentration of hydrogen-containing acidic species; introductory equations often write these as \(H^+\), although hydrated ions are present in real aqueous solution. The remaining negative ion is the acid residue or anion. Examples include chloride \(Cl^-\), nitrate \(NO_3^-\), sulfate \(SO_4^{2-}\), and carbonate \(CO_3^{2-}\).
| Acid formula | Name | Acid-residue ion |
|---|---|---|
| \(HCl\) | hydrochloric acid | \(Cl^-\), chloride |
| \(HNO_3\) | nitric acid | \(NO_3^-\), nitrate |
| \(H_2SO_4\) | sulfuric acid | \(SO_4^{2-}\), sulfate |
| \(H_2CO_3\) | carbonic acid | \(CO_3^{2-}\), carbonate |
2. Salts and charge balance
A salt is an ionic compound containing positive ions other than \(H^+\) and negative ions other than \(OH^-\) in the introductory classification. The total positive and negative charges in a formula unit must sum to zero. Use the smallest whole-number ion ratio.
\(Ca^{2+}\) and \(Cl^-\)
One calcium ion needs two chlorides: \(CaCl_2\).
\(Al^{3+}\) and \(O^{2-}\)
Least common charge 6 gives \(Al_2O_3\).
\(Al^{3+}\) and \(SO_4^{2-}\)
Two aluminium ions and three sulfates give \(Al_2(SO_4)_3\).