JAMB - Chemistry (1981 - No. 45)
The scale formation in a kinetic used for boiling water is caused by the presence in water of?
calcium sulphate
calcium carbonate
calcium hydrogen carbonate
calcium hydroxide
magnesium sulphate
Explanation
The scale is produced when soluble Ca(HCO3)2 breaks down on heating to form insoluble CaCO3
eqn Ca (HCO3)2(aq) -----> CaCO3 (s) + CO2 (g) + H2O (l)
eqn Ca (HCO3)2(aq) -----> CaCO3 (s) + CO2 (g) + H2O (l)