Question

Identify each of the following conditions as acidic, basic, or neutral. (a) \(\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]<\left[\mathrm{OH}^{-}\right]\) (b) \(\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]=1.0 \times 10^{-4} M\) (c) \(\left[\mathrm{OH}^{-}\right]=1.0 \times 10^{-3} M\)

Short answer

(a) Basic (b) Acidic (c) Basic

Step-by-step solution

Analyze (a)

For condition (a), the concentration of \(\mathrm{H}_{3} \mathrm{O}^{+}\) ions is less than the concentration of \(\mathrm{OH}^{-}\) ions. Therefore, it's an alkaline or basic solution, because the higher concentration of \(\mathrm{OH}^{-}\) ions implies a lower pH.

Analyze (b)

For condition (b), \(\left[\mathrm{H}_{3} \mathrm{O}^{+}\right] = 1.0 \times 10^{-4} M\), which is higher than the neutral solution concentration of \(1.0 \times 10^{-7} M\). Therefore, it's an acidic solution, because the higher concentration of \(\mathrm{H}_{3} \mathrm{O}^{+}\) ions implies a lower pH.

Analyze (c)

For condition (c), \(\left[\mathrm{OH}^{-}\right] = 1.0 \times 10^{-3} M\). This is larger than the neutral concentration of \(1.0 \times 10^{-7} M\), implying that there is a lower concentration of \(\mathrm{H}_{3} \mathrm{O}^{+}\) ions. Therefore, it's a basic solution.

Key concepts

pH Concentration

Understanding pH is crucial when analysing substances to determine whether they're acidic, basic, or neutral. The pH scale quantifies how acidic or basic a solution is, with a range typically from 0 to 14. Low pH values (less than 7) indicate acidic conditions, high pH values (more than 7) suggest basic conditions, and a pH of 7 is neutral, which is the pH of pure water at 25°C.

pH concentration refers to the concentration of hydronium ions \(\mathrm{H}_3\mathrm{O}^{+}\) in a solution. To find the pH mathematically, we use the formula \(\text{pH} = -\log \left[\mathrm{H}_3\mathrm{O}^{+}\right]\). Conversely, to find the concentration from the pH, we reverse this equation: \(\left[\mathrm{H}_3\mathrm{O}^{+}\right] = 10^{-\text{pH}}\). Identifying pH concentration helps determine the acidity or basicity of a solution, key for many chemical reactions and processes.

Acid-Base Chemistry

Acid-base chemistry is a fundamental concept of chemistry that involves the balance between hydronium \(\mathrm{H}_3\mathrm{O}^{+}\) and hydroxide \(\mathrm{OH}^{-}\) ions. Acids are substances that increase the concentration of hydronium ions when dissolved in water, while bases are those that increase the concentration of hydroxide ions.

The balance between these ions is critical; when their concentrations are equal \(\left[\mathrm{H}_3\mathrm{O}^{+}\right] = \left[\mathrm{OH}^{-}\right]\), the solution is neutral. If the concentration of hydronium ions is higher, the solution is acidic, and if the concentration of hydroxide ions is higher, the solution is basic. This relationship is vital in various applications, from industrial processes to biological systems.

Hydroxide Ions

Hydroxide ions \(\mathrm{OH}^{-}\) play an essential role in determining the basicity of a substance. When a base dissolves in water, it releases hydroxide ions, which can combine with hydronium ions to form water. This neutralization reaction is a fundamental aspect of acid-base chemistry.

The concentration of hydroxide ions in a solution is a direct indicator of its basicity. More hydroxide ions mean a higher pH and thus a more basic solution. It's important to note that increasing the hydroxide ion concentration decreases the concentration of hydronium ions, due to the equilibrium of water dissociation.

Hydronium Ions

Hydronium ions \(\mathrm{H}_3\mathrm{O}^{+}\), are indicative of acidity in a solution. Acids release these ions when they are dissolved in water. The more hydronium ions present, the lower the pH, and the more acidic the solution is considered to be.

Measuring the concentration of hydronium ions provides direct information about the solution's pH. In the exercise solutions provided, the pH is inferred from the concentration of these ions: a higher hydronium ion concentration indicates an acidic condition, while a lower concentration indicates a basic condition. In a neutral condition, the concentration of hydronium ions is equal to that of hydroxide ions, which is typically \(1.0 \times 10^{-7} M\) at 25°C.