When you add HCl to Ca(OH)2, something interesting happens. HCl is a strong acid, which means it completely dissociates in water, releasing H+ ions. On the other hand, Ca(OH)2 is a strong base, also known as lime or calcium hydroxide, and it dissolves in water to produce OH- ions.
Now, when we mix these two substances together, the H+ ions from the HCl will react with the OH- ions from the Ca(OH)2. This reaction is called neutralization, and it occurs because the H+ ions are attracted to the negatively charged OH- ions.
The neutralization reaction between H+ and OH- ions forms water (H2O). The H+ ions combine with the OH- ions to produce H2O molecules. This reaction is highly favorable because it helps to balance the charges between the positive and negative ions.
As more H+ ions from the HCl react with the OH- ions, more water is formed. This drives the equilibrium of the reaction to the right, meaning that more of the solid Ca(OH)2 will dissolve in the water.
The increased concentration of H+ ions in the solution also makes it more acidic. This can be observed by testing the pH of the solution, which will decrease as more H+ ions are added.
When you add HCl to a saturated solution of Ca(OH)2, the acid protons react with the OH- ions, forming water and driving the equilibrium towards the dissolution of more Ca(OH)2. This results in an increase in the concentration of H+ ions in the solution and a decrease in pH.