${\mathrm{P}}^{\mathrm{H}}$ of a weak acid solution in 0.1 M solution is 4.3. What is the ${\mathrm{P}}^{\mathrm{H}}$ in 0.01M solution?

(nearest integer)

$$\begin{gathered} {\mathrm{P}}^{\mathrm{H}}=\frac{1}{2}\left({\mathrm{P}}^{{\mathrm{K}}_{\mathrm{a}}}-\log \mathrm{c}\right) \mathrm{c}=0.1, \mathrm{M}={10}^{-1}, {\mathrm{P}}^{\mathrm{H}}=4.3 \\ 4.3=\frac{1}{2}\left({\mathrm{P}}^{{\mathrm{K}}_{\mathrm{a}}}-\log {10}^{-1}\right)=\frac{1}{2}\left({\mathrm{P}}^{{\mathrm{K}}_{\mathrm{a}}}+1\right)\Rightarrow {\mathrm{P}}^{{\mathrm{K}}_{\mathrm{a}}}+1=8.6 {\mathrm{P}}^{{\mathrm{K}}_{\mathrm{a}}}=7.6 \\ \mathrm{c}={10}^{-2}=0.01\mathrm{M} \end{gathered}$$

${\mathrm{P}}^{\mathrm{H}}=\frac{1}{2}\left(7.6-\log {10}^{-2}\right)=\frac{9.6}{2}=4.8 4.$ nearest value is 5.