Question

The pH of weak monoacidic base is 11.2, its OH⁻ ion concentration is:

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

Answer 1

The Correct Option is A

Given, pH = 11.2

We know the relation between pH and pOH: \[ \text{pH} + \text{pOH} = 14 \]

Substituting the given pH value: \[ \text{pOH} = 14 - 11.2 = 2.8 \]

Now, the hydroxide ion concentration is given by: \[ [\text{OH}^-] = 10^{-\text{pOH}} \]

Substituting the value of pOH: \[ [\text{OH}^-] = 10^{-2.8} \]

We can simplify this as: \[ 10^{-2.8} = 10^{-3 + 0.2} = 10^{-3} \times 10^{0.2} \]

Since \( 10^{0.2} \approx 1.585 \), \[ [\text{OH}^-] = 1.585 \times 10^{-3} \, \text{mol dm}^{-3} \]

Therefore, the hydroxide ion concentration is: \[ [\text{OH}^-] = 1.585 \times 10^{-3} \, \text{mol dm}^{-3} \]