As the H3O+ ion concentration of a solution increases, the pH of the solution

As the H3O+ ion concentration of a solution increases, the pH of the solution

• A. Increases
• B. Remains the same
• C. Decreases
• D. Becomes undefined

Answer: (C)

pH is a measure of acidity defined by pH = -log10[H3O+]. When the hydronium ion concentration increases, the number inside the logarithm gets larger, and the negative sign makes the overall pH value smaller. In other words, higher [H3O+] means more acidic solution and a lower pH. For example, increasing [H3O+] from 1×10^-5 M to 1×10^-4 M raises the hydrogen ion concentration by a factor of 10, so the pH drops from 5 to 4. Therefore, the pH decreases as the hydronium concentration increases. The pH remains defined for typical aqueous solutions, so it doesn’t become undefined.

pH is a measure of acidity defined by pH = -log10[H3O+]. When the hydronium ion concentration increases, the number inside the logarithm gets larger, and the negative sign makes the overall pH value smaller. In other words, higher [H3O+] means more acidic solution and a lower pH. For example, increasing [H3O+] from 1×10^-5 M to 1×10^-4 M raises the hydrogen ion concentration by a factor of 10, so the pH drops from 5 to 4. Therefore, the pH decreases as the hydronium concentration increases. The pH remains defined for typical aqueous solutions, so it doesn’t become undefined.