Hardness of water.

[JamesF]

A water analysis determined: Na+=0.001 moles/L;Ca+2=0.003 moles/L;Cl-=0.015 moles/L and NO3-=0.006 moles/L. What is the hardness of this water sample in mg/L as CaCO3? Any help with this problem would be greatly appreciated.

[kingchemist]

I would think you would take the [Ca2+] and work out CaCO3 equivalent from this.
0.003 mole/L [Ca2+] is equivalent to 0.003 mole/L CaCO3

If using Ca=40,C=12 and O=16 then 1 mole weighs 100g (use the values your course requires)
Then 0.003 mole = 0.003x100 weighs 0.3g
so concentration = 0.3g/L = 300mg/L