Corrected entry: Chapter Nine: Hermione says that Snape mentioned Polyjuice Potion "in class a few weeks ago." He said that the potion is described in the "Moste Potente Potions" book. This is pure plot convenience. There is no practical reason for Snape to tell second-year students about a risky, complicated potion, nor mention a book that contains the recipe. He is cruel and unfair, but not blatantly irresponsible.
lionhead
7th Sep 2023
Correction: Why would Snape think any second-year student would actually be able to make the potion? Not irresponsible at all for him to mention an advanced potion like that to second-year students. Mentioning it doesn't seem all that unlikely either; he is, after all, the potions teacher. Maybe he just listed a few complicated potions as examples compared to easier potions the second years are taught to make.
lionhead
I would like to add that Snape believes a "select few" students will appreciate the art of potions. He may have mentioned this potion and book, in case it catches the attention of a "worthy" student.