You now have five ways to find moles of a substance. Two of those methods are from this unit: n = PV/RT and n = V/molar V both for gases only. Consult the text p. 501-506, and answer p.503 #25-27; p.506 (see margin) #29, 32, 33; p.511 #36, 39. If you feel very comfortable with this concept, try the extension question, p.500 #2.