Multiple Choice
15.3 grams of sodium benzoate is dissolved in 250 mL of water. What is the pH of the resultant solution if the Kb of benzoate ion is 1.5 x 10^-10?
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17. Acid and Base Equilibrium
pH of Weak Bases
Multiple Choice
What determines the pH of a solution formed when a salt dissociates in water and the resulting acid or base is weak?
A
The initial pH of the water before the salt is added.
B
The temperature of the solution.
C
The concentration of the salt in the solution.
D
The relative strengths of the conjugate acid and conjugate base.
Verified step by step guidance1
Understand that when a salt dissociates in water, it can form a conjugate acid and a conjugate base. These species can affect the pH of the solution.
Identify the ions produced from the dissociation of the salt. For example, if the salt is sodium acetate (NaC2H3O2), it dissociates into Na⁺ and C2H3O2⁻ ions.
Determine the conjugate acid and conjugate base formed. In the case of sodium acetate, the acetate ion (C2H3O2⁻) can act as a base and accept a proton to form acetic acid (HC2H3O2), which is a weak acid.
Evaluate the relative strengths of the conjugate acid and conjugate base. The pH of the solution is influenced by whether the conjugate acid or base is stronger. If the conjugate base is stronger, the solution will be more basic; if the conjugate acid is stronger, the solution will be more acidic.
Consider the equilibrium constant (Ka or Kb) for the conjugate acid or base. A larger Ka indicates a stronger acid, while a larger Kb indicates a stronger base. This helps predict the direction of the pH change.
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