Question

item 30: acid base titration curve analysis
titration of 0.100 mol/l h₂so₃(aq) with 0.750 mol/l naoh(aq)

1. identify the following for this experiment:

a. what is the sample?
b. what is the titrant?

1. region a

a. what is this called?
b. what other zones on this graph behave the same way?
c. what two entities are required in this experiment to give this region?

1. region b

a. what is this called?
b. why is this point special, what is unique about this point?
c. write the reaction that occurred to get to this point
d. what indicator would be appropriate for this point

1. region d

a. write the reaction that occurred to get to this point
b. what indicator would be appropriate for this point

Explanation:

Step1: Identify sample and titrant

In an acid - base titration, the sample is the solution being analyzed and the titrant is the solution of known concentration added to it.
The sample is $0.100\ mol/L\ H_{2}SO_{3(aq)}$ and the titrant is $0.750\ mol/L\ NaOH_{(aq)}$.

Step2: Analyze Region A

Region A is the buffer region. Other buffer - like zones are regions where there is a significant amount of both acid and its conjugate base. Here, the two entities required are $H_{2}SO_{3}$ and its conjugate base $HSO_{3}^{-}$.

Step3: Analyze Region B

Region B is the first equivalence point. It is special because it is the point where the moles of $NaOH$ added are equal to the moles of $H^{+}$ from the first dissociation of $H_{2}SO_{3}$. The reaction is $H_{2}SO_{3}+NaOH = NaHSO_{3}+H_{2}O$. An appropriate indicator could be methyl orange as it changes color in the acidic - range around the pH of the first equivalence point of a polyprotic acid - strong base titration.

Step4: Analyze Region D

The reaction to reach Region D (second equivalence point) is $NaHSO_{3}+NaOH = Na_{2}SO_{3}+H_{2}O$. An appropriate indicator for this basic - range equivalence point could be phenolphthalein.

Answer:

1.
a. The sample is $0.100\ mol/L\ H_{2}SO_{3(aq)}$.
b. The titrant is $0.750\ mol/L\ NaOH_{(aq)}$.
2.
a. Region A is a buffer region.
b. Other buffer - like zones are regions with significant amounts of acid and conjugate base.
c. The two entities are $H_{2}SO_{3}$ and $HSO_{3}^{-}$.
3.
a. Region B is the first equivalence point.
b. It is special because moles of $NaOH$ equal moles of $H^{+}$ from first dissociation of $H_{2}SO_{3}$.
c. $H_{2}SO_{3}+NaOH = NaHSO_{3}+H_{2}O$
d. Methyl orange.
4.
a. $NaHSO_{3}+NaOH = Na_{2}SO_{3}+H_{2}O$
b. Phenolphthalein.