1987 Volume 36 Issue 2 Pages 103-108
Simple and rapid methods have been developed for the determination of water hardness by colorimetry using ο-cresolphthalein complexone as a color development agent. In the determination of calcium hardness, 8-hydroxyquinoline-5-sulfonic acid was used as a masking agent for magnesium, whereas sodium citrate was used for the determination of total hardness in order to equalize the molar absorptivities of calcium and magnesium. To a transparent cylindric measurement vessel with 25 ml volume, a 20 ml of water sample and a reagent for the determination of calcium or total hardness were added, and the vessel was vigorously shaken for a miunte. The determination of calcium hardness (25150 ppm as CaCO3) and total hardness (25200 ppm as CaCO3) were easily carried out by comparing the color of sample solution to a standard color scale. In the presence of a yellow dye, color of the sample solution turns from yellow to red with an increase of water hardness. The results of the determination of calcium and total hardness in water by the proposed method agreed well with those by AAS.
