Question

Complete the following steps to determine the nutrition provided by your tested water. a.   Beginning with the density of water at 4 °C, which is 1.00 g/mL, demonstrate that the units of ppm can also be expressed as mg of solute per L of water (mg/L). b.   Based on your average water hardness (in ppm), how many mg of CaCO3 are in each liter of your tested water? c.   How many mg of Ca2+ are in each liter of your tested water

Answer 1

a. Considering the density to be 1.00 g/mL, you know that one gram of water is actually 1 ml of water as well. Now, one liter contains 1000 ml of water, or 1000 g of water, which is the same thing. If we transform said g of water to mg, we should multiply the amount times 1000, which will give us a total of 1000000 mg for each liter of water. The fact that a million mg are contained in one liter is why we call them ppm (parts per million).

b. Here, you should have a total ppm of CaCO3 for your tested water. If, for example, you have 200 ppm of said salt, this would mean that you actually have 200 mg of CaCO3 in one liter of water, or 0.2 g if you want it in grams.

c. following our example, if you have 0.2 g of CaCO3, this is the 100% of your molecule. If we decompose the molecule:

Element	Amount	Mol. Weight	Total	Percentage
Ca	1	40.078	40.078	40.04%
C	1	12.0107	12.0107	12.00%
O	3	15.9994	47.9982	47.96%

Now you would have a 40.04% of the actual 200mg worth of Ca, therefore (200mg)(0.4004)= 80.08 mg of Ca.

**Remember you have to change all calculations with your actual measurements.