Hardness

Visual Kits

Range MDL Method Kit Catalog No. Refill Catalog No.
50-500 ppm as CaCO3 50 ppm EGTA (calcium) K-1705
2-20 ppm as CaCO3 2.0 ppm EDTA (total) K-4502
20-200 ppm as CaCO3 20 ppm EDTA (total) K-4520
100-1000 ppm as CaCO3 100 ppm EDTA (total) K-4585

Methods

 

Hardness is a measure of the mineral content of water. Calcium and magnesium are the most common minerals that contribute to hardness. Hard water causes scaling in boilers and other industrial equipment, and diminishes the effectiveness of soaps and detergents.

 

The EGTA Method (calcium)

Reference: West, T. S., DSC, Ph.D., Complexometry with EDTA and Related Reagents, 3rd. ed., pp. 46, 164 (1969).

 

The EGTA method is specific for calcium hardness. The EGTA titrant in alkaline solution is employed with a zincon indicator. Results are expressed as ppm (mg/L) CaCO3.

 

Shelf-life: eight months. Although the reagent itself is stable, the end point indicator has a limited shelf-life. We recommend stocking quantities that will be used within seven months.

 

The EDTA Method (total)

References: APHA Standard Methods, 22nd ed., Method 2340 C- 1997. USEPA Methods for Chemical Analysis of Water and Wastes, Method 130.2 (1983).

 

The total hardness method is applicable to drinking, surface, boiler, and brine waters.

 

The EDTA titrant is employed in alkaline solution with a calmagite indicator. This method determines the combined calcium and magnesium concentration of a sample. If no magnesium is present, the end point of the titration normally appears sluggish. Results are expressed as ppm (mg/L) CaCO3.