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When CO2 combines with water it forms carbonic acid. How does this explain the phenol red result?
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18. Aqueous Equilibrium
Acid-Base Indicators
Multiple Choice
What is the pH of the solution after titrating 25.00 mL of 0.22 M HC2H3O2 with 25.00 mL of 0.22 M NaOH?
A
7.00
B
3.00
C
8.72
D
4.74
Verified step by step guidance1
Identify the type of titration: This is a titration of a weak acid (acetic acid, HC2H3O2) with a strong base (NaOH).
Calculate the moles of acetic acid and NaOH: Use the formula \( \text{moles} = \text{concentration} \times \text{volume} \). For both solutions, \( \text{moles} = 0.22 \text{ M} \times 0.025 \text{ L} \).
Determine the reaction completion: Since the moles of acetic acid and NaOH are equal, they will completely neutralize each other, forming water and the acetate ion (C2H3O2^-).
Recognize the resulting solution: After neutralization, the solution contains the acetate ion, which is the conjugate base of acetic acid. This is a buffer solution at the equivalence point.
Calculate the pH: At the equivalence point of a weak acid-strong base titration, the pH is determined by the hydrolysis of the acetate ion. Use the formula \( \text{pH} = 7 + \frac{1}{2} \log K_a \) where \( K_a \) is the acid dissociation constant for acetic acid.
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