Question

Why does aspirin dissolve in water?

Answer 1

Solubility. Aspirin is only slightly soluble in water and acidic solutions such as is present in the stomach. Aspirin contains polar functional groups which can form hydrogen bonds with polar water molecules.

Answer 2

In hot water, aspirin is fairly easily dissolved but not so much in cold water.

In my first year labs, the students make aspirin in hot water solutions and then cool the beakers of aspirin solution in ice to crystallize the aspirin out.  Some aspirin is still in solution and thus lost in the process but close to all of it comes out of solution at ice temperatures.  Typical yields is in the 90% range so assuming all the possible losses incurred by the students (spilling, filtering losses, sticking to beakers, etc.) I would say the amount that actually is lost because it does not precipitate out at ice temperatures is very small.

So, in conclusion.  aspirin is soluble in hot water and slightly soluble in ice-cold water and ranging in between the two extremes as the temperatures range between boiling and freezing points.