Question

The pH of weak monoacidic base is 11.2, its OH\(^-\) ion concentration is:

• A. \( 1.585 \times 10^{-3} \) mol dm\(^{-3}\)
• B. \( 3.010 \times 10^{-11} \) mol dm\(^{-3}\)
• C. \( 3.010 \times 10^{-3} \) mol dm\(^{-3}\)
• D. \( 1.585 \times 10^{-11} \) mol dm\(^{-3}\)

Hint:

To calculate the OH\(^-\) concentration from pOH, use the formula \( [OH^-] = 10^{-pOH} \).

Answer 1

The Correct Option is A

Step 1: Use the pH and OH\(^-\) concentration relationship.
We know that for a weak base, \( pH + pOH = 14 \). The pH is given as 11.2, so we calculate pOH: \[ pOH = 14 - pH = 14 - 11.2 = 2.8 \] Next, the OH\(^-\) concentration is given by: \[ [OH^-] = 10^{-pOH} = 10^{-2.8} = 1.585 \times 10^{-3} \text{ mol dm}^{-3} \] Thus, the correct answer is (A).