Question

A weak base is \(5 \%\) dissociated in its 0.01 M solution. Calculate the dissociation constant.

• A. \(3.5\times 10^{-6}\)
• B. \(2.0\times 10^{-5}\)
• C. \(2.3\times 10^{-4}\)
• D. \(2.5\times 10^{-5}\)

Hint:

Use Ostwald's dilution law for a weak electrolyte with small degree of dissociation.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
For a weak base with small dissociation, \(K_b = C\alpha^2\).

Step 2: Values
\(C = 0.01\) M and \(\alpha = 5\% = 0.05\).

Step 3: Calculation
\(K_b = 0.01\times(0.05)^2 = 0.01\times 0.0025 = 2.5\times 10^{-5}\)

Final Answer:
The dissociation constant is \(2.5\times 10^{-5}\). \[ \boxed{\text{(D) }2.5\times 10^{-5}} \]