PH Scale

Definition

The pH scale is a measure of the acidity or basicity of a solution, ranging from 0 to 14. It is a logarithmic scale that quantifies the concentration of hydrogen ions (H+) in a solution, with lower values indicating higher acidity and higher values indicating higher basicity or alkalinity. The pH scale is a fundamental concept in understanding Brønsted-Lowry acids and bases, as well as the relationship between pH and pOH, and the behavior of polyprotic acids.

5 Must Know Facts For Your Next Test

1. The pH scale ranges from 0 to 14, with 7 being the neutral point where the concentration of H+ and OH- ions are equal.
2. Solutions with a pH less than 7 are considered acidic, while solutions with a pH greater than 7 are considered basic or alkaline.
3. The pH scale is logarithmic, meaning that each unit change in pH represents a ten-fold change in the concentration of H+ ions.
4. The relationship between pH and pOH is defined by the equation: pH + pOH = 14, where pOH is the negative logarithm of the hydroxide ion concentration.
5. Polyprotic acids, such as carbonic acid (H2CO3) and phosphoric acid (H3PO4), can donate multiple protons and have multiple pH endpoints, which are important in understanding their behavior.

Review Questions

• Explain how the pH scale is related to the Brønsted-Lowry definition of acids and bases.
  • The pH scale is directly connected to the Brønsted-Lowry definition of acids and bases. Acids are substances that donate protons (H+ ions) to other substances, resulting in a lower pH value. Bases are substances that accept protons, leading to a higher pH value. The pH scale quantifies the concentration of H+ ions in a solution, allowing us to determine the relative acidity or basicity of a substance based on its position on the pH scale.
• Describe the relationship between pH and pOH, and how this relationship is used to determine the nature of a solution.
  • The relationship between pH and pOH is defined by the equation pH + pOH = 14. This means that as the pH of a solution increases, the pOH (the negative logarithm of the hydroxide ion concentration) decreases, and vice versa. This relationship is used to determine the nature of a solution. If the pH of a solution is less than 7, it is considered acidic, as the concentration of H+ ions is greater than the concentration of OH- ions. If the pH is greater than 7, the solution is considered basic or alkaline, with a higher concentration of OH- ions than H+ ions. A pH of 7 indicates a neutral solution, where the concentrations of H+ and OH- ions are equal.
• Analyze how the pH scale is used to understand the behavior of polyprotic acids, such as carbonic acid (H2CO3) and phosphoric acid (H3PO4).
  • Polyprotic acids, like carbonic acid and phosphoric acid, can donate multiple protons (H+ ions) in a stepwise fashion. This means they have multiple pH endpoints, which can be understood using the pH scale. The pH scale allows us to track the progressive deprotonation of these acids as the concentration of H+ ions changes. For example, carbonic acid (H2CO3) can donate two protons, forming bicarbonate (HCO3-) and then carbonate (CO3^2-) ions. The pH scale helps us identify the predominant species present at different pH values, which is crucial for understanding the behavior and properties of polyprotic acids.

Related terms

Acidity: The measure of the concentration of hydrogen ions (H+) in a solution, with lower pH values indicating higher acidity.

Basicity: The measure of the concentration of hydroxide ions (OH-) in a solution, with higher pH values indicating higher basicity or alkalinity.

Neutralization:

The process of combining an acid and a base to produce a neutral solution with a pH of 7.