pH Assignment Vocabulary

Reference Materials and Scope

Reference materials for studying acid-base balance, acidosis, alkalosis, and pH fundamentals include:

• Merck Manuals: Overview of Acid-Base Balance, Acidosis Symptoms, Alkalosis Symptoms
• Bozeman Science: Acids, Bases and pH
• Textbook: Chapter 2, Section 4 (pages $69$–$71$) and Chapter 27, Sections 5 and 6 (pages $835$–$843$)

Biological Significance of Acid-Base Balance

Maintaining a stable pH in body fluids is essential for proper physiological functioning and survival. An extreme change in body fluid pH causes body proteins to denature, which disrupts structural and enzymatic properties and causes cells to stop working properly.

Disruptions in systemic acid-base balance lead to specific symptom profiles depending on whether the condition is acidosis or alkalosis:

• Acidosis Symptoms: Resulting from an excess of acid or a deficit of base in body fluids, symptoms include headache, confusion, tiredness, weakness, swelling, coma, and shortness of breath.
• Alkalosis Symptoms: Resulting from an excess of base or a deficit of acid in body fluids, symptoms include confusion, dizziness, and muscle spasms or twitching.
• Worst-Case Scenario: Uncorrected, severe shifts in body fluid pH ultimately lead to coma or death.

Fundamentals of the pH Scale

The pH scale measures the concentration of hydrogen ions ($H^+$) in a solution, indicating how acidic or basic (alkaline) that solution is.

• Neutral Value: A pH value of $7$ (or $7.0$) represents a neutral solution.
• Acidic Range: Acids possess a pH value strictly below $7$ (covering values from $0$ to $6$).
• Basic Range: Bases (alkalines) possess a pH value strictly above $7$ (covering values from $8$ to $14$).

On a standard numerical pH scale spanning from $0$ to $14$:

• The number $0$ represents the greatest concentration of hydrogen ions ($H^+$) and corresponds to the strongest acid.
• The number $14$ represents the least concentration of hydrogen ions ($H^+$) and corresponds to the strongest base.
• Moving closer to $0$ indicates an increasingly strong acid with a higher $H^+$ concentration, whereas moving closer to $7$ from below indicates a weaker acid. Moving closer to $14$ indicates an increasingly strong base with a lower $H^+$ concentration, whereas moving closer to $7$ from above indicates a weaker base.

Mathematical Principles of pH Differences

The pH scale is logarithmic. A difference of $1$ unit on the pH scale represents a $10\text{-fold}$ ($10^1$) difference in the number of hydrogen ions ($H^+$) and in relative acid or base strength.

• Comparing pH 2 to pH 3: A solution with a pH of $2$ has $10$ times more $H^+$ ions than a solution with a pH of $3$. Because the strongest acid is closest to $0$, a pH of $2$ is a $10$ times stronger acid than a pH of $3$. Conversely, because the weakest acid is closest to $7$, a pH of $3$ is a $10$ times weaker acid than a pH of $2$
• Comparing pH 10 to pH 8: A solution with a pH of $10$ has $100$ ($10^2$) times fewer $H^+$ ions than a solution with a pH of $8$. Because the strongest base is closest to $14$, a pH of $10$ is a $100$ times stronger base than a pH of $8$. Conversely, because the weakest base is closest to $7$, a pH of $8$ is a $100$ times weaker base than a pH of $10$
• Comparing pH 4 to pH 8: A solution with a pH of $4$ has a difference of $4$ units compared to a solution with a pH of $8$ ($8 - 4 = 4$). Consequently, a pH of $4$ has $10^4 = 10,000$ times more $H^+$ ions than a pH of $8$. Between these two, pH $4$ is the stronger acid, whereas pH $8$ is the weaker acid (and is mildly basic).

Human Blood pH Regulation

Human physiological mechanisms maintain blood pH within an extremely precise range to ensure cellular homeostasis.

• Blood pH Set Point: The standard normal set point for blood pH is $7.4$
• Normal Blood pH Range: The normal allowable range for human blood pH is strictly between $7.35$ and $7.45$