91影视

The endpoint is what is actually measured, which is a physical change in the solution as indicated by the above-mentioned indication or instrument. There is a small variation between the titration's endpoint and its equivalency point. This type of error is known as an indication error, and it is unreliable.

(a)

The required volume of base can be calculated as

$$\begin{gathered} \left[{\mathrm{OH}}^{-}\right]\mathbf{=}{\mathbf{10}}^{\mathbf{-}\mathbf{4}\mathbf{.}\mathbf{4}} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\left(0.1000M\right)\frac{\mathbf{V}}{\mathbf{50}\mathbf{+}\mathbf{10}\mathbf{+}\mathbf{V}} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{V}\mathbf{=}\mathbf{}\mathbf{0}\mathbf{.}\mathbf{024}\mathbf{}\mathbf{mL} \end{gathered}$$

Thus, the volume of base is required to reach pH ${}^{\mathbf{9}\mathbf{.}\mathbf{6}}$is ${}^{\mathbf{0}\mathbf{.}\mathbf{024}\mathbf{}\mathbf{mL}}$.

(b)

The pH before the equivalent point is ${}^{\mathbf{8}\mathbf{.}\mathbf{8}}$.

$$\begin{gathered} \mathbf{8}\mathbf{.}\mathbf{8}\mathbf{=}\mathbf{6}\mathbf{.}\mathbf{27}\mathbf{+}\mathbf{log}\frac{\left[A^{-}\right]}{\left[\mathrm{HA}\right]} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\frac{\left[A^{-}\right]}{\left[\mathrm{HA}\right]} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\mathbf{339} \end{gathered}$$

Titration:${}^{\mathbf{HA}\mathbf{+}{\mathbf{OH}}^{\mathbf{-}}}$

$\mathbf{鈫�}{\mathbf{A}}^{\mathbf{鈥�}}\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}$

Relative initial quantities: 10 ${}^{\mathbf{V}}$ - -

Relative final quantities:${}^{\mathbf{10}\mathbf{-}\mathbf{V}}$ - ${}^{\mathbf{V}}$ -

Next, the ratio

$$\begin{gathered} \frac{\left[A^{-}\right]}{\left[\mathrm{HA}\right]}\mathbf{}\mathbf{=}\mathbf{339} \\ \frac{\mathbf{V}}{\mathbf{10}\mathbf{-}\mathbf{V}}\mathbf{}\mathbf{=}\mathbf{339} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\mathbf{9}\mathbf{.}\mathbf{97}\mathbf{}\mathbf{mL} \end{gathered}$$

Therefore, the indicator error is ${}^{\mathbf{10}\mathbf{-}\mathbf{9}\mathbf{.}\mathbf{97}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{03}\mathbf{}\mathbf{mL}}$.