Concept explainers
Determine pH at the equivalence point in the titration of 41.0 mL 0.096 M formic acid with 0.108 M
(a) 12.94
(b) 7.00
(c) 5.76
(d) 8.24
(e) 1.06
Interpretation:
The pH at the equivalence point in the titration of formic acid with sodium hydroxide is to be determined.
Concept introduction:
When a weak acid is titrated against a strong base, the conjugate base of the weak acid is formed in the reaction:
This conjugate base now acts as a Bronsted base and reacts with water to form a weak acid and hydroxide ions, according to the reaction:
Here,
The relationship between
Where,
The formula to calculate the pOH of the solution from the concentration of hydroxide ions is
pH is the measure of acidity of a solution, which depends on the concentration of hydronium ions and the temperature of the solution. The relationship between pH and pOH is
Molarity
Rearrange this equation in terms of moles as
When volume is given in
Answer to Problem 2KSP
Correct answer: Option (d).
Explanation of Solution
Given information:
The concentration of formic acid
Reason for correct option:
From the given values of concentration and volume of formic acid, calculate the number of millimoles of formic acid, using equation (5) as shown:
Being a strong base,
At equivalence point, during the titration process, millimoles of weak acid must be equal to the millimoles of the strong base. Thus,
As, the concentration of
Thus, total volume of the solution containing
During titration, there is complete neutralization of weak acid. Thus, the moles of weak acid reacted is equal to the moles of its conjugate base formed. Therefore,
Thus, concentration of the conjugate base
The anion
From table
Now, prepare an equilibrium table and represent each of the species in terms of
Now, substitute these concentrations in equation (2) as
Since the value of
Thus,
Now, substitute the value of
Substitute this value of pOH in equation (4) to calculate the pH of the solution
Therefore, the equivalence pH of the solution is
Reason for incorrect options:
Since
Since
Since
Since
Therefore, options (a), (b), (c), and (e) are incorrect.
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Chapter 16 Solutions
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