# What is the concentration of pure water at 298*K given a "density" of 1.00*g*mL^-1?

In the case of pure water, we can assume density to be $1.0 g . c {m}^{-} 3$, so 1000 ml of water will be 1000 g. Molar mass of water is 18.015 g/mol, so 1000 g contains 1000/18.015 = 55.509 mol per litre.