Question

Identify each of the following conditions as acidic, basic, or neutral. (a) \(\left[\mathrm{OH}^{-}\right]=1.0 \times 10^{-11} M\) (b) \(\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]=1.0 \times 10^{-9} M\) (c) \(\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]>\left[\mathrm{OH}^{-}\right]\)

Short answer

Every condition is acidic.

Step-by-step solution

Interpretation of part (a)

Evaluate the concentration of \( \mathrm{OH}^{-} = 1.0 \times 10^{-11} M \). This is lesser than the standard neutral concentration ( \(1.0 \times 10^{-7} M\) ). Hence, as \( \mathrm{OH}^{-} \) concentration is lesser, \( \mathrm{H}_{3} \mathrm{O}^{+} \) concentration would be higher and the solution is acidic.

Interpretation of part (b)

Check the concentration of \( \mathrm{H}_{3} \mathrm{O}^{+} = 1.0 \times 10^{-9} M \). Here, the concentration is more than the neutral concentration. So, the solution is acidic.

Interpretation of part (c)

As stated, \( \mathrm{H}_{3} \mathrm{O}^{+} \) concentration is more than \( \mathrm{OH}^{-} \). If \( \mathrm{H}_{3} \mathrm{O}^{+} \) concentration is more, it indicates an acidic solution.

Key concepts

Understanding pH Calculation

The term 'pH' stands for 'potential of hydrogen' and it represents the acidity or basicity of a solution. It is a logarithmic scale that ranges from 0 to 14, with 7 being neutral, numbers below 7 indicating acidity, and numbers above 7 indicating basicity.

The pH value is calculated by taking the negative base 10 logarithm of the hydronium ion concentration ([H_{3}O^{+}]), represented as:
For example, if the hydronium ion concentration is 1.0 × 10^-9 M, the pH is calculated as:-9),which equals 9. Therefore, this solution is considered basic, because its pH is above 7.

Understanding how to calculate pH is crucial for identifying whether solutions are acidic, basic, or neutral. Moreover, this skill is essential in a wide range of applications from chemistry laboratories to the food industry, and to environmental science.

Exploring Hydroxide Ion Concentration

Hydroxide ions (OH⁻) play a significant role in determining the basicity of a solution. The hydroxide ion concentration is often given in molarity (M), which is moles per liter. In a neutral solution, water dissociates to equal concentrations of hydronium and hydroxide ions, each being 1.0 × 10^-7 M.

When the hydroxide ion concentration is greater than 1.0 × 10^-7 M, the solution is basic. Conversely, when it is less than 1.0 × 10^-7 M, the solution is acidic due to the relative increase in hydronium ions. These concepts are essential in processes such as water purification, where balanced pH levels are critical for safe drinking water.

Hydronium Ion Concentration and Its Implications

The concentration of hydronium ions (H_{3}O⁺) is a direct measure of a solution's acidity. For neutral conditions, the concentration of hydronium ions is 1.0 × 10^-7 M. A higher concentration than this indicates an acidic environment, while a lower concentration suggests a basic environment.

For instance, a hydronium ion concentration of 1.0 × 10^-9 M implies a pH of 9, which means the solution is less acidic than neutral water and therefore basic. The control of hydronium ion concentrations is vital in chemical manufacturing and biochemical reactions, where the acidity or basicity can influence reaction rates and product formation.

The Nuts and Bolts of Acid-Base Chemistry

At the heart of acid-base chemistry is the relationship between hydronium (H_{3}O⁺) and hydroxide (OH⁻) ions. In an acidic solution, the concentration of hydronium ions exceeds the concentration of hydroxide ions. Basic solutions are just the opposite, with hydroxide ions outnumbering hydronium ions.

Understanding this fundamental balance is key to numerous chemical applications, including neutralization reactions, titrations, and buffer solutions. These principles are also applied in environmental monitoring to maintain the pH balance in ecosystems and avoid the detrimental effects of acid rain or over-alkalinity in bodies of water.