Acs

It states "only the COOH group reacts with the NaOH" because the Acetyl group also reacts with it naturally, which forms sodium acetate (as far as I'm concerned) besides the sodium salicylate, which makes the whole reaction a 1:2 ratio in regards to Aspirin : NaOH. But when only the COOH group reacts with it as the task says, you don't have to take the Na-Acetate part into consideration, the ratio of the reactants are 1:1 I suppose, resulting in: C8H7O2COOH + NaOH = C8H7O2COONa + H2O.