An experiment was carried out to determine the hardness of domestic water. A few drops of pH = 10 buffer were added to a 100 cm³ sample of the water. This sample was titrated against 0.01 M edta(aq) using Eriochrome Black T indicator and gave a titre of 33.8 cm³. Under these circumstances both Mg²⁺ and Ca²⁺ ions react with edta. A second 100 cm³ sample was titrated against the edta solution after 5.0 cm³ of 0.1 M NaOH(aq) and a few drops of murexide indicator had been added. Under these conditions only the Ca²⁺ ions react with the edta and a titre of 27.5 cm³ was obtained. Determine the hardness of the water sample in terms of the concentration of the Mg²⁺ and of the Ca²⁺ ions.