Question

What is the concentration of hydrogen ion in the solution when the concentration of hydroxyl ion is \(0.08\) mol / dm\(^3\) at \(298\) K ?

• A. \(0.125\) mol/L
• B. \(0.125\times 10^{-12}\) mol/L
• C. \(0.0125\) mol/L
• D. \(0.125\times 10^{-10}\) mol/L

Hint:

Use \(K_w = [\text{H}^+][\text{OH}^-] = 10^{-14}\) at 298 K.

Answer 1

The Correct Option is B

Step 1: Idea:
Compute pOH first, then pH, then the hydrogen ion concentration.

Step 2: Steps:
\[ \text{pOH} = -\log(0.08) = 1.097 \]
\[ \text{pH} = 14 - 1.097 = 12.903 \]
\[ [\text{H}^+] = 10^{-12.903} = 1.25\times10^{-13}\ \text{mol/L} = 0.125\times10^{-12}\ \text{mol/L} \]
Only option B has this value. The strong base means a tiny acid concentration, so options A and C are impossible.

Final Answer:
$[\text{H}^+] = 0.125\times10^{-12}$ mol/L, which is option (B). \[ \boxed{0.125\times10^{-12}\ \text{mol/L}} \]