microtest® Test Kit Specifications

microtest RH 5 Residual Hardness

Titrimetric Test for

Residual Total Hardness

limit = 5 mg/L CaCO3

Product Code609200
ContentsIndicator, 15 mL
Cuvette, 4 mL
Instructions for Use
Analytical MethodComplexometric Titration: At pH = 10, earthalkali metals (calcium, magnesium and strontium) form a pink coloured complex with certain indicator dyes (e.g. eriochrome black T, calmagite). On adding EDTA (ethylenediamine tetraacetic acid), these metals prefer to complex with EDTA, and release the indicator dye. As the uncomplexed dye exhibits a blue colour, the titration endpoint is indicated by a sudden colour change from pink to pure blue. The amount of EDTA added is directly proportional to the concentration of Ca2+, Mg2+ and Sr2+ ions. Results are expressed as calcium carbonate CaCO3.
This kit used a mixed Buffer/Indicator/Titration Solution, one drop of which on a 2 mL water sample indicates, whether the threshold of 5 mg/L has been exceeded:
colour blue: residual hardness is less than 5 mg/L
colour red: residual hardness is greater than 5 mg/L
Number of Tests400
InterferencesOther metals like Al, Fe, Mn or Cu interfere by complexing the indicator dye and not releasing it any more. The indicator becomes "blocked" and a colour change at the titration endpoint does not occur.
Measuring RangeThis test does not have a measuring range, but indicates whether the residual of total hardness exceeds the threshold of 5 mg/L.
Shelf Life2 years
ApplicationsMonitoring of residual total hardness levels in softened and R/O water (boiler feed water).