The Solution Is Acidic When:
A. POH > 7
B. PH > 7
C. [OH-] > 1.0 x 10-7
D. [H+] < 1.0 x 10-7
The Correct Answer and Explanation is:
The correct answer is D. [H+] < 1.0 x 10⁻⁷.
Explanation:
To understand why D is the correct answer, we need to review some key concepts about acids, bases, pH, and ion concentration in aqueous solutions.
pH and Acidity
- pH is a measure of the hydrogen ion concentration ([H⁺]) in a solution.
- pH is calculated as: $$
\text{pH} = -\log[H^+]
$$ - A solution is acidic if the concentration of hydrogen ions is greater than that in pure water, meaning: $$
[H^+] > 1.0 \times 10^{-7} \text{ M}
$$ - A solution is neutral if: $$
[H^+] = 1.0 \times 10^{-7} \text{ M}
$$ (This corresponds to a pH of 7.) - A solution is basic (alkaline) if: $$
[H^+] < 1.0 \times 10^{-7} \text{ M}
$$
Since the pH scale is logarithmic, a small change in hydrogen ion concentration causes a significant change in pH value.
Explanation of Each Option
- A. POH > 7
This is incorrect because POH (pOH) measures the hydroxide ion concentration ([OH⁻]). For acidic solutions, pOH is less than 7, not greater. When a solution is acidic, it has more H⁺ ions and fewer OH⁻ ions, so pOH is low. - B. pH > 7
This is incorrect because a pH greater than 7 indicates a basic (alkaline) solution, not acidic. - C. [OH⁻] > 1.0 x 10⁻⁷
This is incorrect because a hydroxide ion concentration greater than 1.0 x 10⁻⁷ means the solution is basic, not acidic. Acidic solutions have lower [OH⁻]. - D. [H⁺] < 1.0 x 10⁻⁷
This is actually the condition for a basic solution, so it seems contradictory.
Correction and Clarification:
The correct answer should be:
The solution is acidic when [H⁺] > 1.0 x 10⁻⁷ M.
It looks like there is a mistake in the options provided. The option for acidic solution should be when hydrogen ion concentration is greater than 1.0 x 10⁻⁷, not less.