Question

If \([\text{H}_3\text{O}^+]\) of a solution is \(1\times 10^{-4}\). What is the value of pOH at \(298\,\text{K}\) ?

• A. \(4\)
• B. \(10\)
• C. \(12\)
• D. \(14\)

Hint:

First get pH from the hydronium concentration, then use pH + pOH = 14.

Answer 1

The Correct Option is B

Step 1: Understand the concept
At 298 K, the ion product of water gives \(\text{pH} + \text{pOH} = 14\). So we need the pH first.

Step 2: Find pH
\[ \text{pH} = -\log(1 \times 10^{-4}) = 4 \]

Step 3: Find pOH
\[ \text{pOH} = 14 - 4 = 10 \]

Step 4: Check the options
The value 4 is the pH, not the pOH, so (A) is a mix-up. The value 12 would mean pH 2, and 14 would mean pH 0. Neither fits a hydronium concentration of \(10^{-4}\) M. The solution is acidic, so the pOH must be larger than 7, and 10 satisfies this.

Final Answer:
The pOH is 10. This is option (B). \[ \boxed{\text{(B) }10} \]