Calcium Hardness

The Method is applicable to determine the calcium ion content in water samples aswell as the solid samples.

The Disodium salts of ethylene diamine tetra acetic acid ( Na2 EDTA) form slighly ionised colourless, stable complex with calcium ions. Muroxide is dark purple in the absence of calcium but with calcium form alight salamen coloured complex which has inonisation constant higher than Na2 EDTA complex. Hence by using muroxide indicator a solution containg ions may be titrated with Na2EDTA. the optimum pH = 10

Muroxide (NH4C8H4N5O6, or C8H5N5O6.NH3), also called ammonium purpurate or MX, is the ammonium salt of purpuric acid.

Muroxide in its dry state has the appearance of a reddish purple powder, slightly soluble in water. In solution, its color ranges from yellow in strong acidic pH through reddish-purple in weakly acidic solutions to blue-purple in alkaline solutions. The pH for titration of calcium is 11.3.

Molarity of EDTA solution is 0.01 M ; mL of 0.01 M EDTA = 1 mg of CaCO3
EDTA molarity x EDTA volume (L) = Ca+2 molarity x Ca+2 volume (L)