Question

A titration is carried out by slowly adding a solution of $0.125MNaOH\left(aq\right)$ to a flask containing $25.00mL$ of a solution of $H_{2}S{O}_4\left(aq\right)$. The titration continues until the equivalence point is reached, as shown by phenolphthalein indicator.
Which of the following correctly describes the change in the concentration of sodium ions, $\left[N{a}^{+}\right]$, and the concentration of sulfate ions. $\left[S{O}_4^{2-}\right]$, in the flask during the titration?

• A. $\left[N{a}^{+}\right]$ and $\left[S{O}_4^{2-}\right]$ both increase.
• B. $\left[N{a}^{+}\right]$ increases, but $\left[S{O}_4^{2-}\right]$ decrease.
• C. $\left[N{a}^{+}\right]$ increases, but $\left[S{O}_4^{2-}\right]$ remains the same.
• D. $\left[N{a}^{+}\right]$ and $\left[S{O}_4^{2-}\right]$ both decrease.

Answer 1

Answer: (A)

$\left[N{a}^{+}\right]$ and $\left[S{O}_4^{2-}\right]$ both increase.

$NaOH\left(aq\right)+H_{2}S{O}_4\left(aq\right)⟶N{a}^{+}\left(aq\right)+S{O}_4^{2-}\left(aq\right)+H_{2}O$

$NaOH$ is added continuously till $H_{2}S{O}_4$ is getting neutralized and hence concentration of both $N{a}^{+}$ and $S{O}_4^{2-}$ increases.