Salicylic acid (2-hydroxybenzoic acid) contains both a carboxylic acid proton and a…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Salicylic acid (2-hydroxybenzoic acid) contains both a carboxylic acid proton and a phenolic proton. The pKa for removal of the carboxylic acid proton is 2.98 at 25 °C. No numerical value is provided for removal of the phenolic proton.
(1) Identify which proton (carboxylic or phenolic) is expected to be lost first as strong base is added. State the structural reason for your choice.
(2) Estimate the approximate pKa of the phenolic proton and justify your estimate by comparing structural stabilization of the two possible conjugate bases.
(3) Sketch a qualitative titration curve (pH vs. volume of added 0.100 M NaOH) for a solution of salicylic acid, labeling the two equivalence points and the buffering regions. No numerical scale is required, but important features must be indicated.
(4) For each equivalence point, describe the dominant conjugate base present and explain why that species is significantly weaker as a base than hydroxide ion.