Sciencebase.com is the place to be for reactive science communication on the web, and it's free. The name comes from the generic term for the underlying scientific infrastructure ...
Designers, manufacturers and installers of laboratory fume cupboards, LEVs, extraction systems and all associated equipment.
ChemBuddy - chemical calculators
Easy to use programs for pH calculation, concentration conversion, solution preparation, equation balancing and stoichiometry with built in dissociation constants and density tables databases.
All you want to know about pH meters, pH measurements and pH electrodes. History, theory and practice, links to models and manufacturers.