water hardness - xxiii lo im. nauczycieli tajnego ...23lo.lublin.pl/comenius/water_hardness.ppt ·...

Prepared by Anna Danczowska-Burdon

Water hardness is caused by the presence of salts dissolved in water, primarily calcium and magnesium.It causes the formation of boiler scale during water boiling and bad soap foaming.

carbonate hardness – also called temporary water hardness is caused by the presence of carbonates, hydrocarbonates and hydroxides of calcium and magnesium.

Noncarbonate hardness – caused by the presence of Ca2+, Mg2+ of other cations and anions like: Al3+, Fe2+, Fe3+, Cu2+, Cl-, SO4

2-, NO3

-, which do not decompose and do not precipitate during boiling water.

General water hardness – is the summary content of calcium, magnesium and other ions

Caused by the presence of hydrocarbonates, carbonates and hydroxides of calcium and magnesium. It can be removed by water boiling.

Ca(HCO3)2 → CaCO3 + H2O + CO2 Mg(HCO3)2 → MgCO3 + H2O + CO2

Clark’s Method, Blacher’s Method, Warta-Pfeifer Method, method using EDTA

(versenate) separate

determination of calcium and magnesium ions