Question

Hard/ Soft water:

Why is CaCO₃ present in hot water, but not in cold? My prfoessor talked about he has his water softerner only for hot water, but the cold water is not passed through a water softner. Can you please explain showing step by step equilibrium reactions and where the equilibrium is favored. Here are a few equations that might help your thought process. I guess I would just like an explaination as to why hot vs cold and what each reaction is telling you

CaCO₃ (s)+CO₂ (aq)+H2O (l) ⇌ Ca²⁺ (aq) + 2HCO₃⁻(aq)

Ca^{2+ +} CO_3^2- +H₂O ⇌ HCO₃- + OH^-

HCO₃- + H₂O ⇌ H₂CO₃ + OH^-

H₂CO₃ ⇌ H₂O + CO₂

Answer 1

calcium salts such as calcium carbonate and calcium bicarbonates both are more soluble in hot water than in cold water.so hot water does not cause the pricipitation.the given equilibrium of carbonate and bicarbonate is driven by carbonate and bicarbonate only not by CO₂, because CO₂ dissolve in water.

when the tempertaure of water raises the co2 removed from water as gas and there will be increase in concentration of dissolevd carbonates.

where as in cold water, or water cools, then dissolved carbonates precipitate out and can accumilates on surfaces( taps ..etc) and cold water carres more gases than in hot water.

precipitation softening carroed out at ambient temperatures only , and known as cold lime softening .