Perchloric acid, \(\mathrm{HClO}_{4}\), is a strong acid. (a) Write the chemical equation for the reaction between perchloric acid and water. (b) List all species present in an aqueous solution of perchloric acid in order of concentration, highest to lowest. (c) Calculate the concentration of all species (except \(\mathrm{H}_{2} \mathrm{O}\) ) present in a \(0.100 \mathrm{M} \mathrm{HClO}_{4}\) solution. (d) What is the \(\mathrm{pH}\) of this solution?

Understanding strong acids is crucial for comprehending their behavior in water. A strong acid is one that completely dissociates into its ions when dissolved in water. Perchloric acid, symbolized as \(\mathrm{HClO}_{4}\), is a prime example of a strong acid.

Dissociation refers to the process where an acid's molecules split into cations and anions. This complete dissociation is what characterizes strong acids, resulting in a high concentration of hydronium ions \(\mathrm{H}_{3}\mathrm{O}^{+}\) in the solution. This leads to low pH values and indicates the strength of the acid in terms of its capacity to donate protons to water, effectively increasing the \(\mathrm{H}_{3}\mathrm{O}^{+}\) concentration.

The chemical equation represents the reaction between substances through chemical formulas. For the reaction between perchloric acid and water, correct representation is vital for understanding the process. The balanced chemical equation is:
\[\mathrm{HClO}_{4} \, (aq) + \mathrm{H}_{2}\mathrm{O} \, (l) \rightarrow \mathrm{H}_{3}\mathrm{O}^{+}_{\, (aq)} + \mathrm{ClO}_{4}^{-}_{\, (aq)}\]

In this equation, \(\mathrm{HClO}_{4}\) (perchloric acid) reacts with \(\mathrm{H}_{2}\mathrm{O}\) (water) to produce \(\mathrm{H}_{3}\mathrm{O}^{+}\) (hydronium ions) and \(\mathrm{ClO}_{4}^{-}\) (perchlorate ions), illustrating the products and their states in the reaction.

An aqueous solution contains solute particles dissolved in water. Perchloric acid in water forms an aqueous solution where several species are present. Following the chemical equation outlined earlier, the primary species in perchloric acid's aqueous solution are hydronium ions \(\mathrm{H}_{3}\mathrm{O}^{+}\) and perchlorate ions \(\mathrm{ClO}_{4}^{-}\), alongside water molecules.

When you have a strong acid, like perchloric acid, the species must be listed in order of concentration. Typically, the solvent water is present in the largest amount, followed by the ions produced by the acid's dissociation, which are present in equal concentrations in the case of a monoprotic acid such as \(\mathrm{HClO}_{4}\).

The pH scale is a logarithmic measure of the hydrogen ion concentration and is a vital parameter in determining how acidic or basic a solution is. To calculate the pH of an aqueous solution, we use the formula:
\[\mathrm{pH} = -\log_{10} [\mathrm{H}_{3}\mathrm{O}^{+}]\]

For a 0.100 M solution of perchloric acid, the concentration of hydronium ions is 0.100 M, since there is a one-to-one ratio of \(\mathrm{HClO}_{4}\) dissociating into \(\mathrm{H}_{3}\mathrm{O}^{+}\) and \(\mathrm{ClO}_{4}^{-}\) ions. Therefore, you simply plug in the concentration of hydronium ions into the pH equation to find that the pH is 1.00. This low pH value reflects the high acidity of the solution, a characteristic of strong acids in aqueous solution.