1. The problem statement, all variables and given/known data A sample of water is known to have 190 g/m^3 Ca2+ and 84 g/m^3 Mg2+. What is the hardness of the water in mg CaCO3/L? 2. Relevant equations Hardness = (Ca2+) + (Mg2+) 3. The attempt at a solution I need to convert my units into mg CaCO3/L or Normality before summing up the values. The problem is I do not understand how to convert to either. If I'm converting to mg CaCO3/L do I need a molar mass? And when do I use it? As for normality I do not understand what a "weight equivalence" is so I can't convert to that either. Thanks a lot.