Question

Using the assumptions we ordinarily make in calculating the pH of an aqueous solution of a weak acid, calculate the pH of a 1.0 × 10^-6 M solution of hypobromous acid (HBrO, K_a = 2 × 10^-9). What is wrong with your answer? Why is it wrong? Without trying to solve the problem, tell what has to be included to solve the problem correctly?

Short answer

Answer

pH of the given phenol solution comes out to be 7.4. Acids cannot have pH more than 7.

Step-by-step solution

 Calculation of [H+] for HOBr

For weak acids like HOBr,

$$\begin{gathered} \left[{\mathrm{H}}^{+}\right]=\sqrt{Ka\times C} \\ \left[H^{+}\right]=\sqrt{2\times {10}^{-9}\times 1\times {10}^{-8}}=4.4\times {10}^{-8} \end{gathered}$$

pH of HOBr

$$\begin{gathered} pH=-\log \left[H^{+}\right] \\ pH=\log \left(4.4\times {10}^{-8}\right) \end{gathered}$$