Multiple Choice
A 35.0-mL sample of 0.150 M acetic acid (CH3COOH, Ka=1.8×10⁻⁵) is titrated with 0.150 M NaOH solution. Calculate the pH after 35.0 mL of the base have been added.
18. Aqueous Equilibrium
Titrations: Weak Acid-Strong Base
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Consider the titration of 25.00 mL of 0.150 M hydrazoic acid (Ka = 1.90 x 10^-5) with 0.200 M NaOH. What is the pH of the solution at the equivalence point of the titration?
A
8.50
B
9.25
C
7.00
D
10.00
Verified step by step guidance1
Identify the type of titration: This is a weak acid (hydrazoic acid) being titrated with a strong base (NaOH). At the equivalence point, the acid is completely neutralized, forming its conjugate base.
Calculate the moles of hydrazoic acid initially present: Use the formula \( \text{moles} = \text{concentration} \times \text{volume} \). Convert the volume from mL to L before calculating.
Determine the volume of NaOH required to reach the equivalence point: Since the reaction is 1:1, the moles of NaOH needed will be equal to the moles of hydrazoic acid. Use the concentration of NaOH to find the volume required.
At the equivalence point, the solution contains only the conjugate base (the azide ion). Calculate the concentration of the azide ion by dividing the moles of azide by the total volume of the solution at the equivalence point.
Calculate the pH of the solution: Use the formula for the hydrolysis of the conjugate base \( \text{A}^- \) to find \( \text{OH}^- \) concentration, then convert \( \text{OH}^- \) concentration to pOH, and finally to pH using \( \text{pH} = 14 - \text{pOH} \).
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