If there are 8.0 mg of dissolved O2 per liter of H2O at 20 degrees C and 1 atm, calculate the number of moles of molecular O2 and the molarity of dissolved O2 per liter of H2O.
moles = grams/molar mass
8.0 mg = 0.008 g
moles = 0.008g/32 g/mol
Then M = mols/L.