Most courses in Chemistry, especially those at the college/university level, assume that their students have had prior courses in general science, and often in physics, which provide them with an understanding of important concepts such as significant figures, units of measure, treatment measurement error, density and buoyancy.  But  if most of that has receded into the fuzzy past, the six sections of this unit will bring you up to speed.  Neglect this stuff at your peril —  it will come up in one way or another in any Chemistry course you take!

The Chem1 Virtual Textbook is a resource for General Chemistry aimed mainly at the first-year university level.
It offers a more comprehensive, organized, and measured approach than is found in most standard textbooks. It should also be accessible to advanced high-school courses, and helpful as review material for students in more advanced courses in chemistry, biology, geology, and engineering.