Question

Compare the magnitudes of \(\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]\) and \(\left[\mathrm{OH}^{-}\right]\) in aqueous solutions that are acidic, basic, and neutral.

Short answer

Acidic: \\([ \mathrm{H}_{3}\mathrm{O}^{+}] > [\mathrm{OH}^{-}]\\); Basic: \\([ \mathrm{H}_{3}\mathrm{O}^{+}] < [\mathrm{OH}^{-}]\\); Neutral: \\([ \mathrm{H}_{3}\mathrm{O}^{+}] = [\mathrm{OH}^{-}]\\).

Step-by-step solution

Understanding Acidic, Basic, and Neutral Solutions

In aqueous solutions, pH and pOH define if the solution is acidic, basic, or neutral. A neutral solution has a pH of 7, meaning \([\mathrm{H}_{3}\mathrm{O}^{+}] = [\mathrm{OH}^{-}]\). An acidic solution has a pH less than 7, meaning \([\mathrm{H}_{3}\mathrm{O}^{+}] > [\mathrm{OH}^{-}]\). A basic solution has a pH greater than 7, meaning \([\mathrm{H}_{3}\mathrm{O}^{+}] < [\mathrm{OH}^{-}]\).

Key concepts

Acidic Solutions

Acidic solutions are characterized by an abundance of hydrogen ions, or hydronium ions, represented as \([\mathrm{H}_{3}\mathrm{O}^{+}]\). In such solutions, the concentration of hydrogen ions exceeds that of hydroxide ions \([\mathrm{OH}^{-}]\). This is due to the nature of acids, which donate protons \(\mathrm{H}^{+}\) in solution, leading to the formation of hydronium ions. The pH scale, ranging from 0 to 14, measures how acidic or basic a solution is. For acidic solutions, the pH value is less than 7.
One can often find acids like vinegar, lemon juice, or stomach acid in everyday life, all having a pH less than 7.

• High concentration of \([\mathrm{H}_{3}\mathrm{O}^{+}]\)
• Low pH (less than 7)
• Examples include lemon juice, vinegar

To summarize, when a solution has more \([\mathrm{H}_{3}\mathrm{O}^{+}]\) than \([\mathrm{OH}^{-}]\), it is classified as acidic. As a result, the solution’s pH is lower, making it more corrosive and capable of breaking down substances.

Basic Solutions

Basic solutions are the opposite of acidic solutions and have a higher concentration of hydroxide ions \(\mathrm{OH}^{-}\) compared to hydronium ions \(\mathrm{H}_{3}\mathrm{O}^{+}\). When a solution is basic, its pH value is greater than 7, indicating excess hydroxide ions in the solution. Bases can accept protons or release hydroxide ions into the solution, which accounts for the increase in \(\mathrm{OH}^{-}\) concentration.

• High concentration of \(\mathrm{OH}^{-}\)
• pH greater than 7
• Examples include baking soda, soap

You will find basic solutions in many household products. For example, soap and baking soda solution are both basic. These solutions often feel slippery and can neutralize acids. In summary, when there are more hydroxide ions than hydronium ions, a solution is basic. This results in a higher pH and often a bitter taste and a slippery feel.

Neutral Solutions

Neutral solutions have equal concentrations of hydronium ions and hydroxide ions. This perfect balance gives them a pH of exactly 7. Water is the most common example of a neutral solution, making it neither acidic nor basic. In a neutral solution, the interaction between \(\mathrm{H}_{3}\mathrm{O}^{+}\) and \(\mathrm{OH}^{-}\) is in equilibrium, meaning neither ion is in excess.

• Equal \(\mathrm{H}_{3}\mathrm{O}^{+}\) and \(\mathrm{OH}^{-}\) concentrations
• Exactly pH 7
• Example includes pure water

Neutral solutions often serve as a baseline in experiments, allowing scientists to detect changes in acidity or basicity when substances are added. Since neutral solutions do not favor either acidic or basic characteristics, they are often used in dilution and during pH testing to gauge the properties of other materials.