Multiple Choice
In a titration of a weak acid with a strong base, how is the pH determined before reaching the equivalence point?
18. Aqueous Equilibrium
Titrations: Weak Acid-Strong Base
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For a titration of a weak acid with a strong base, the pH at the equivalence point ________.
A
is less than 7
B
is equal to 7
C
is greater than 7
D
depends on the acid used
E
depends on the Ka of the acid used
Verified step by step guidance1
Understand that in a titration of a weak acid with a strong base, the equivalence point is reached when the moles of base added equal the moles of acid initially present.
At the equivalence point, the weak acid has been completely neutralized to form its conjugate base. This conjugate base can react with water to form hydroxide ions, making the solution basic.
Recognize that the pH at the equivalence point is determined by the strength of the conjugate base formed. Since the conjugate base of a weak acid is relatively strong, it will increase the pH above 7.
Consider the role of the acid dissociation constant (Ka) of the weak acid. A smaller Ka indicates a weaker acid and a stronger conjugate base, which will result in a higher pH at the equivalence point.
Conclude that for a titration of a weak acid with a strong base, the pH at the equivalence point is greater than 7 due to the formation of a basic solution from the conjugate base of the weak acid.
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