Why we take #"CaCO"_3# as standard to determine the hardness of water?
There are two reasons.
Water passing over limestone deposits dissolves some of the minerals.
The concentrations of
2. The calculation is easy
We measure the concentrations of individual ions
We usually express the hardness of water in "ppm" (parts per million or milligrams per kilogram of water or milligrams per litre).
The molar mass of
Thus we can express the total hardness of water as
The total hardness expressed as