To determine the concentration of the calcium hydroxide, we need to relate the acid used by using the chemical reaction involved. The chemical reaction would be
Ca(OH)2 + 2HCl = CaCl2 + 2H2O
We calculate as follows:
Mole HCl = 0.1 M (.0178 L) = 1.78x10^-3 mol HCl
Mole Ca(OH)2 reacted = 1.78x10^-3 mol HCl ( 1 mol Ca(OH)2 / 2 mol HCl ) = 8.4x10^-4 mol
Conc'n Ca(OH)2 = 8.4x10^-4 mol / .025 L = 0.04 M