Some Basic Concepts of Chemistry - Result Question 2
2. In an acid-base titration, 0.1 MHCl solution was added to the NaOH solution of unknown strength. Which of the following correctly shows the change of pH of the titration mixture in this experiment?
(2019 Main, 9 April II)
(a) $(D)$
(b) $(A)$
(c) $(B)$
(d) $(C)$
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Answer:
Correct Answer: 2. (b)
Solution: The graph that shows the correct change of pH of the titration mixture in the experiment is
In this case, both the titrants are completely ionised.
$$ \mathrm{HCl}+\mathrm{NaOH} \rightleftharpoons \mathrm{NaCl}+\mathrm{H}_2 \mathrm{O} $$
As $\mathrm{H}^{\oplus}$ is added to a basic solution, $\left[\mathrm{OH}^{\ominus}\right]$ decreases and $\left[\mathrm{H}^{+}\right]$ increases. Therefore, pH goes on decreasing. As the equivalence point is reached, $\left[\mathrm{OH}^{\ominus}\right]$ is rapidly reduced. After this point $\left[\mathrm{OH}^{\ominus}\right]$ decreases rapidly and pH of the solution remains fairly constant. Thus, there is an inflexion point at the equivalence point.
The difference in the volume of NaOH solution between the end point and the equivalence point is not significant for most of the commonly used indicators as there is a large change in the pH value around the equivalence point. Most of them change their colour across this pH change.
BETA
