Ca2+ ion may exist in the aqueous (aq) state.
This is the case when the anion is nitrate ion, for
instance.
This is not the case when the anion is sulfate ion, for
instance.
At 'A' levels, you have to compare the endothermic lattice
dissociation enthalpy and associated (increase in) entropy change,
versus the exothermic solvation (hydration) enthalpy and
associated (decrease in) entropy change.
If the solution enthalpy and entropy change is feasible, (as in
the case of calcium nitrate solution), then you will get Ca2+(aq)
and NO3-(aq).
If the solution enthalpy and entropy change is
not feasible, (as in the case of calcium sulfate solution),
then you will get CaSO4(s).
At 'O' levels, you simply memorize which salts are water
soluble and which are not, then write your ionic equation
accordingly.
>>> calcium hydroxide is sparingly soluble.
<<<
Correct.
The portion which is aqueous is called limewater.
The portion which is solid is called slaked lime.
CaO(s) = Lime
Ca(OH)2(s) = Slaked lime.
Ca(OH)2(aq) = Limewater.
CaCO3(s) = Limestone (small pieces called marble
chips).
NaOH(aq) + Ca(OH)2(aq) = Soda Lime.
KOH(aq) + Ca(OH)2(aq) = Potash Lime.
Qn) When you bubble carbon dioxide into limewater, a white ppt
is observed. Write equations to explain this.
CO2(g) + H2O(l) --> H2CO3(aq)
H2CO3(aq) + Ca(OH)2(aq) --> 2H2O(l) + CaCO3(s) (white
ppt)