recrystallization of benzamide

i guess your recrystallization involves boiling of impure benzamide with NaOH, followed by filtering the insoluble impurities, or am i wrong?

the hydrogen on amide-H is slightly acidic (see the respective anion and its resonance structure). after boiling with NaOH, it deprotonates to yield soluble sodium salt.

after filtration, excess HCl is added to protonate the anion, yielding uncharged benzamide. the benzamide-N is non-acidic.

solubility of benzamide in water is ~13mg/ml, almost insoluble. therefore, once soluble anion turns into benzamide, it'll precipitate or at least, turning the mixture milky (due to formation of small solid particles of benzamide).