What is (i) soap scum, (ii) boiler scale? Give the related chemical equations.
(i) Soap Scum: Soap scum is a solid residue that forms when the calcium and magnesium ions in hard water react with soap. The chemical equation for the reaction is:
Ca2+ (hard water) + 2C17H35COO- (soap) → (C17H35COO)2Ca (soap scum)
(ii) Boiler Scale: Boiler scale refers to the hard, insoluble deposits that form on the internal surfaces of boilers and heat exchangers due to the precipitation of calcium and magnesium salts from hard water. The chemical equation involves the reaction between calcium and magnesium ions and bicarbonate ions:
Ca2+ (hard water) + 2HCO3- (bicarbonate) → CaCO3 (scale) + CO2 + H2O
Mg2+ (hard water) + 2HCO3– (bicarbonate) → MgCO3 (scale) + CO2 + H2O