Answer:
7.44x10⁻³ mol/L and 744 ppm
Explanation:
Let's assume that the hardness of the water is totally from Ca⁺² ions only(the hardness is the measure of Ca⁺² and Mg⁺² ions). The titration with EDTA will form a complex. The EDTA is always in 1:1 proportion, so the number of moles of it will be the number of moles of Ca⁺², which will be the number of moles of CaCO₃.
n = 0.0124 L * 0.0300 mol/L
n = 3.72x10⁻⁴ mol
The molarity is the number of moles divided by the volume (0.05 L)
M = 3.72x10⁻⁴/0.05
M = 7.44x10⁻³ mol/L
1 part per million = 1 mg/L. The molar mass of the CaCO₃ is 100 g/mol, so the mass of it is:
m = 3.72x10⁻⁴ mol * 100 g/mol
m = 0.0372 g = 37.2 mg
Then, the ppm:
37.2/0.05 = 744 ppm
