Question

Calculate the pH of a \(0.001\,M\) \(NaOH\) solution at \(298\,K\).

• A. \(11\)
• B. \(10\)
• C. \(3\)
• D. \(7\)

Hint:

For strong bases, concentration of \(OH^-\) equals the base concentration. First compute pOH, then use \(pH + pOH = 14\).

Answer 1

The Correct Option is A

Concept: For a strong base like \(NaOH\): \[ \text{pOH} = -\log[OH^-] \] and \[ \text{pH} + \text{pOH} = 14 \] at \(298\,K\).

Step 1: Determine the hydroxide ion concentration. Since \(NaOH\) is a strong base, it completely dissociates: \[ NaOH \rightarrow Na^+ + OH^- \] \[ [OH^-] = 0.001 = 10^{-3} \]

Step 2: Calculate pOH. \[ pOH = -\log(10^{-3}) \] \[ pOH = 3 \]

Step 3: Find pH. \[ pH + pOH = 14 \] \[ pH = 14 - 3 \] \[ pH = 11 \]