This video demonstrates how to obtain calcium oxide (CaO) and how it reacts with water. Calcium oxide may be obtained by heating of calcium carbonate (CaCO3).
Calcium carbonate is the main component of eggshells (according to some sources, an eggshell consists ~90% of CaCO3). To prove it, an eggshell fragment was immersed in hydrochloric acid (HCl). The calcium carbonate contained in the eggshell reacted with the acid, releasing carbon dioxide (CO2) in the form of gas bubbles from the eggshell surface:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
or in ionic form:
CaCO3(t) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
When the eggshell is being heated, the calcium carbonate in it partially decomposes to calcium oxide and carbon dioxide:
CaCO3(s) → CaO(s) + CO2(g)
The products of the heating were dropped in water, giving calcium hydroxide (Ca(OH)2) as a result of a reaction between calcium oxide and water:
CaO(s) + H2O(l) → Ca(OH)2(aq)
Calcium hydroxide dissolves partially and dissociates, resulting in a basic environment:
Ca(OH)2(aq) → Ca2+(aq) + 2OH-(aq)
As indicated by the pink color of the phenolphthalein, the pH of the solution is above 9.