Arrange the following 0.1 M aqueous solutions in order of...

Arrange the following 0.1 M aqueous solutions in order of decreasing pH (highest to lowest).

$$
\mathrm{Ba}\left(\mathrm{NO}_3\right)_2, \quad \mathrm{HNO}_3, \quad \mathrm{NH}_4 \mathrm{NO}_3, \quad \mathrm{Al}\left(\mathrm{NO}_3\right)_3, \quad \mathrm{NaF}
$$

Key Concepts

pH Scale

The pH scale is a logarithmic scale used to quantify the acidity or basicity of a solution. It measures the concentration of hydrogen ions (H?) present, with lower pH values indicating higher acidity and higher pH values indicating greater basicity. Understanding the pH scale is essential for comparing different solutions based on their hydrogen ion concentration.

Salt Hydrolysis

Salt hydrolysis refers to the reaction that occurs when the ions of a dissolved salt interact with water, potentially producing an acidic or basic solution. The pH of the resulting solution depends on whether the anion, the cation, or both react with water to either accept or donate protons. This concept helps determine how salts formed from weak acids or weak bases can alter the pH of a solution.

Strength of Acids and Bases

The strength of an acid or base refers to its degree of dissociation in water. Strong acids and bases ionize completely, leading to predictable pH behaviors, while weak acids and bases only partially dissociate. This distinction is crucial when analyzing aqueous solutions, as it affects the concentration of ions that contribute to the overall pH.

Metal Cation Hydrolysis

Some metal cations, especially those with high charge densities like Al³?, can polarize water molecules and undergo hydrolysis. This process releases hydrogen ions into the solution, causing it to become acidic. Understanding metal cation hydrolysis is important in the study of solution pH, as it explains why certain metal salts yield acidic solutions even when prepared at the same concentration as other salts.

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