PH

Definition

pH, or the potential of hydrogen, is a measure of the acidity or basicity of a solution. It is a scale that ranges from 0 to 14, with 7 being neutral, values less than 7 being acidic, and values greater than 7 being basic or alkaline. The pH of a solution is directly related to the concentration of hydrogen ions (H+) present, and it is a critical factor in many chemical and biological processes.

5 Must Know Facts For Your Next Test

1. The pH scale is logarithmic, meaning a change of one pH unit represents a ten-fold change in the concentration of hydrogen ions.
2. The Henderson-Hasselbalch equation is used to calculate the pH of a solution based on the pKa of the acid and the ratio of the concentrations of the acid and its conjugate base.
3. Biological systems often function optimally within a narrow pH range, and deviations from this range can have significant consequences.
4. The pH of the human body is tightly regulated, with the blood typically maintaining a pH between 7.35 and 7.45, which is slightly basic.
5. Soap, a common household product, works by emulsifying oils and fats, and its effectiveness is influenced by the pH of the solution.

Review Questions

• Explain how the pH of a solution can be predicted using pKa values, as discussed in Section 2.9 on Predicting Acid–Base Reactions from pKa Values.
  • The pH of a solution can be predicted using pKa values through the Henderson-Hasselbalch equation. The pKa of an acid represents its strength, and by knowing the pKa and the ratio of the concentrations of the acid and its conjugate base, the pH of the solution can be calculated. This is useful in predicting the outcome of acid-base reactions, as the relative strengths of the acids and bases involved determine the final pH of the solution.
• Describe the role of pH in the context of biological acids and the Henderson–Hasselbalch equation, as discussed in Section 20.3 on Biological Acids and the Henderson–Hasselbalch Equation.
  • In biological systems, pH is a critical factor in maintaining homeostasis. Many biological molecules, such as proteins and enzymes, function optimally within a specific pH range. The Henderson-Hasselbalch equation is used to understand the pH of biological fluids, such as blood and urine, which are buffered to maintain a relatively constant pH. This equation allows for the prediction of the pH of these solutions based on the pKa values of the relevant acids and the concentrations of the acid and its conjugate base.
• Analyze how the pH of a solution affects the protonation state of biological amines, as discussed in Section 24.5 on Biological Amines and the Henderson–Hasselbalch Equation.
  • The pH of a solution directly affects the protonation state of biological amines, which are important functional groups in many biomolecules. The Henderson-Hasselbalch equation can be used to determine the extent of protonation of these amines based on their pKa values and the pH of the surrounding environment. This is crucial in understanding the behavior and reactivity of biological amines, as their protonation state influences their solubility, interactions with other molecules, and overall biological function.

Related terms

Acid:

A substance that releases hydrogen ions (H+) when dissolved in water, resulting in a pH less than 7.

Base:

A substance that accepts hydrogen ions (H+) when dissolved in water, resulting in a pH greater than 7.

pKa:

The negative logarithm of the acid dissociation constant (Ka), which represents the strength of an acid and is used to predict the pH of a solution.