There aren’t too many words in the English language that, without any change in spelling, can be a noun, verb, or an adjective. Precipitate, one such word, conjures up the image of technicians in lab coats, mixing test tubes.
The precipitate is part of the solution left inside a test tube (or any other container used in labs these days). This definition, though, is not important for the GRE. The verb and adjective definitions, however, are. To be precipitate is to be hasty or rash. To precipitate something, such as a government precipitating a crisis, means to make something happen suddenly.
An amalgam, in the chemistry sense, is an alloy made of mercury and some other metal (formerly used, before the health scare, as part of our dental fillings). Generally speaking, an amalgam is a mixture of two or more things.
In chemistry, a solvent is any substance able to breakdown or dissolve another substance. Outside the lab, to be solvent is to be able to pay off one’s debts. To be insolvent, on the other hand, is not to be able to pay off one’s debts.
In chemistry, when one substance speeds up a chemical reaction, that substance is said to be a catalyst. Broadly speaking, anything that speeds up (or precipitates) an event is a catalyst.
For those who have since forgotten this slippery word, to be mercurial means to change constantly in terms of personality or mood. Typically, we say a mercurial person is moody and unpredictable. When you think of actual mercury—you know, that strange liquid inside thermometers, not the planet—it too is slippery and constantly changing (do not put this to the test—mercury is highly toxic). This poisonous quality, though, did not make it into the definition of mercurial. Someone who is mercurial is just moody.