I'm having trouble figuring out the total water hardness in ppm of equivalent CaCO3. In the lab manual it shows the example equation as (150 mg/1L H2O) x (1 L H2O/1000 mL H2O) x (1.00 mL H2O/1.00 g H2O) x (1 g/1000 mg) = 150 ppm of equivalent CaCO3. The professor stated the equation is correct, but unclear. Clearly if the equation is calculated out, it does not give that result, but gives 1.50 x 10^-4 ppm of equiv CaCO3. Is there something missing? In class the professor showed another way to calculate the problem. First start with millimoles, example (.2713 mmol EDTA) x (1 mmol ions/1 mmol EDTA) / (.02500 mL H2O) = 1.08 mmol (L H2O)^-1 ions Use that number & then use the following formula (1.08 mmol ions / 1 L) x (1 mmol CaCO3 equiv. / 1mmol ions) x 100.0 mg CaCO3 equiv / 1 mmol CaCO3 equiv. = 108 ppm of equivalent CaCO3. So do either of these even look remotely right? If not, which steps am I missing in the calculations.