Calculate the pH of centimolar solution of monoacidic weak base. Which is 10% dissociated in its aqueous solution?
Show Hint
Always pay close attention to terminology. "Decimolar" is 0.1 M, "Centimolar" is 0.01 M, and "Millimolar" is 0.001 M. Also, remember to convert pOH to pH when dealing with bases!
Step 1: Understanding the Concept:
For a weak base, the concentration of hydroxyl ions $[OH^-]$ is given by the product of the initial concentration ($C$) and the degree of dissociation ($\alpha$). Step 2: Formula Application:
"Centimolar" means $C = 10^{-2}$ M.
$\alpha = 10% = 0.1$.
$[OH^-] = C \alpha$. Step 3: Explanation:
$[OH^-] = 10^{-2} \times 0.1 = 10^{-3}$ M.
$pOH = -\log[OH^-] = -\log(10^{-3}) = 3$.
Since $pH + pOH = 14$ at 25°C,
$pH = 14 - 3 = 11$. Step 4: Final Answer:
The pH of the solution is 11.