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A sample of acetic acid is titrated with a standardized NaOH solution. Beyond the end-point of the titration, which of the following must be true?

[tex]\[ HC_2H_3O_2(aq) + NaOH(aq) \longrightarrow NaC_2H_3O_2(aq) + H_2O(l) \][/tex]

Note: [tex]\([X] =\)[/tex] molar concentration of [tex]\(X\)[/tex]

A. [tex]\(\left[ H^+ \right] \ \textless \ [ OH^- ]\)[/tex]

B. [tex]\(\left[ H^+ \right] \ \textgreater \ [ OH^- ]\)[/tex]

C. [tex]\(\left[ H^+ \right] = [ OH^- ]\)[/tex]

Sagot :

GinnyAnsweridn
To understand what happens beyond the end-point of a titration involving acetic acid ([tex]\(HC_2H_3O_2\)[/tex]) and sodium hydroxide ([tex]\(NaOH\)[/tex]), we should consider the stoichiometry and the nature of the substances involved.

Let's analyze the titration process step-by-step:

1. Equation and Reaction:
The balanced chemical equation is:
[tex]\[ HC_2H_3O_2(aq) + NaOH(aq) \longrightarrow NaC_2H_3O_2(aq) + H_2O(l) \][/tex]
Here, acetic acid ([tex]\(HC_2H_3O_2\)[/tex]) reacts with sodium hydroxide ([tex]\(NaOH\)[/tex]) to produce sodium acetate ([tex]\(NaC_2H_3O_2\)[/tex]) and water ([tex]\( H_2O\)[/tex]).

2. Titration End-Point:
The end-point of the titration is reached when the amount of [tex]\(NaOH\)[/tex] added is stoichiometrically equivalent to the amount of [tex]\(HC_2H_3O_2\)[/tex] present. At this point, all of the [tex]\(HC_2H_3O_2\)[/tex] has been neutralized by [tex]\(NaOH\)[/tex], and the solution contains [tex]\(NaC_2H_3O_2\)[/tex] (which is a salt of the weak acid [tex]\(HC_2H_3O_2\)[/tex]) and water.

3. Beyond the End-Point:
Beyond the end-point, excess [tex]\(NaOH\)[/tex] has been added to the solution. This means there is a surplus of [tex]\(OH^-\)[/tex] ions because [tex]\(NaOH\)[/tex] dissociates completely in water:
[tex]\[ NaOH(aq) \rightarrow Na^+ (aq) + OH^- (aq) \][/tex]

4. pH Consideration:
As [tex]\(NaOH\)[/tex] is a strong base and it dissociates completely, the excess [tex]\(OH^-\)[/tex] ions will increase the alkalinity of the solution. In other words, beyond the end-point, the concentration of [tex]\(OH^-\)[/tex] ions will be greater than the concentration of [tex]\(H^+\)[/tex] ions, leading to a basic or alkaline solution.

Given these points, beyond the end-point of titration, the correct statement about the relative concentrations of hydrogen ions ([tex]\(H^+\)[/tex]) and hydroxide ions ([tex]\(OH^-\)[/tex]) is:

[tex]\[ \left[ H ^{+}\right] < [ OH^- ] \][/tex]

This means the solution is basic beyond the end-point because there are more hydroxide ions than hydrogen ions present.
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