JAMB - Chemistry (2011 - No. 12)
Hardness of water is mainly due to the presence of
calcium hydroxide or magnesium hydroxide
calcium trioxocarbonate (IV) or calcium tetraoxosulphate (VI)
sodium hydroxide or magnesium hydroxide
calcium chloride or sodium chloride salts
Vysvetlenie
Salts of Calcium and Magnesium are responsible for hardness of water. Bicarbonates, Carbonates, Chlorides and Sulfates of Calcium and Magnesium causes temporary and permanent hardness.