Question

why wouldn't sodium chloride deprotonate benzoic acid

Answer 1

Ans. Benzoic acid is a weak acid with pKa = 4.20.

An acid donates it proton to anther chemical species that acts a base (or, proton acceptor).

Water has a pKa of 14. It acts as both acid and base depending on the solute being dissolved in it. If the solute is a stronger acid than water, water accepts proton (by acting as base) from the acid. If the solute is a stronger base, water donates protons to the base.

When dissolved in water, benzoic acid donates its proton to water because this solvent acts as a base.

Sodium chloride, NaCl is a salt of strong acid and strong base. It is thus a strong electrolyte, too. The constituent ions Na⁺ and Cl^- do not acts as either proton acceptor or donor. So, NaCl can’t accept a proton from benzoic acid.

Therefore, NaCl alone (say, a drop of benzoic acid is added to a pure sample of NaCl crystals – BUT there is NO water) can’t deprotonate benzoic acid.