99. At room temperature, 8 grams of weak acid HY is dissolved in 400 mL of distilled water. If $K_a = 10^{-5}$ and $\text{HY} = 50 \text{ g·mol}^{-1}$, (ignoring the effect of adding water on the volume of the acid solution,) which statement is correct?
[1)] By doubling the volume of the solution by adding distilled water, the degree of ionization of the acid approximately doubles.
[2)] By doubling the mass of the acid and halving the volume of the solution, the pH of the solution remains constant.
[3)] $[\text{OH}^-]$ in the solution is approximately $5 \times 10^{-13}$.
[4)] The pH of the solution is $3.7$.
\textbf{99.} At room temperature, 8 grams of weak acid HY is dissolved in 400 mL of distilled water. If $K_a = 10^{-5}$ and $\text{HY} = 50 \text{ g·mol}^{-1}$, (ignoring the effect of adding water on the volume of the acid solution,) which statement is correct?
\begin{enumerate}
\item[1)] By doubling the volume of the solution by adding distilled water, the degree of ionization of the acid approximately doubles.
\item[2)] By doubling the mass of the acid and halving the volume of the solution, the pH of the solution remains constant.
\item[3)] $[\text{OH}^-]$ in the solution is approximately $5 \times 10^{-13}$.
\item[4)] The pH of the solution is $3.7$.
\end{enumerate}
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