Final answer:
To find Kb for a weak base, we first calculate pOH and then [OH-] using the provided concentration of the base and pH. We then use this information in the equilibrium expression for Kb to solve for its value.
Step-by-step explanation:
In the given question, we have the concentration of weak base and the pH. We can use the formula for pOH (14 - pH) to find pOH. Then use the formula for pOH to find [OH-]. The concentration of the weak base (B) is given as 0.140 M.
We use the expression for Kb, [OH-][HB+]/[B], where [OH-] and [HB+] are equal (due to the ionization of the base B to form OH- and HB+), and [B] is the initial concentration of base - the concentration of OH-.
Setting these values and solving for Kb can give us the answer. Our answer must be given in two significant figures.
Learn more about Weak Base Equilibrium