6.1.1 Acids

Acids

1. Acids form a class of chemical substances which contain hydrogen ions in aqueous solution, H⁺ (aq), as the only positive ion.
2. Acids are usually classified into mineral or organic acids.

3. Acids are substances that form hydrogen ions when dissolved in water.
4. A hydrogen ion is actually a proton. Therefore, acids are called the proton donors.

Examples
\[HCl\xrightarrow{{{H_2}O}}{H^ + } + C{l^ – }\]
\[HN{O_3}\xrightarrow{{{H_2}O}}{H^ + } + N{O_3}^ – \]
\[{H_2}S{O_4}\xrightarrow{{{H_2}O}}2{H^ + } + S{O_4}^{2 – }\]

The hydrogen ions produced will combine with the water molecule to form hydroxonium ions (H₃O⁺)
\[{H^ + } + {H_2}O \to {H_3}{O^ + }\]
Therefore the reaction can also be written as
\[HCl + {H_2}O \to {H_3}{O^ + } + C{l^ – }\]
\[HN{O_3} + {H_2}O \to {H_3}{O^ + } + N{O_3}^ – \]
\[{H_2}S{O_4} + 2{H_2}O \to 2{H_3}{O^ + } + S{O_4}^{2 – }\]